Buick LeSabre Custom 1994 - 1994 ENGINE PERFORMANCE Self-Diagnostics - Tests W/Codes

Buick LeSabre Custom 1994 - INTRODUCTION

Most engine control problems are the result of mechanical breakdowns, poor electrical connections or damaged vacuum hoses. Before considering the computer system as a possible cause of problems, perform checks and inspections covered in BASIC TESTING j article in this section. Failure to do so may result in lost diagnostic time.

If no faults were found while performing BASIC TESTING, proceed with DIAGNOSTIC PROCEDURE under SELF-DIAGNOSTIC SYSTEM. If no fault codes or only a non-running Code 12 is present and driveability problems exist, proceed to TESTS W/O CODES article in this section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.). If only intermittent codes are present, see INTERMITTENTS in TESTS W/O CODES article in this section.

Buick LeSabre Custom 1994 - SELF-DIAGNOSTIC SYSTEM

NOTE:

Powertrain Control Module (PCM) is also be referred to as Electronic Control Module (ECM) in some diagnostic charts and figures. Terms are used interchangeably.

Control module is equipped with a self-diagnostic system, which detects system failures or abnormalities. When a malfunction occurs, control module will illuminate SERVICE ENGINE SOON light located on instrument panel. SERVICE ENGINE SOON light is also be referred to as the Malfunction Indicator Light (MIL). When malfunction is detected and light is turned on, a corresponding trouble code will be stored in control module memory. To retrieve stored codes, see RETRIEVING CODES (NON-SCAN) . Malfunctions are recorded as hard failures or as intermittent failures.

Buick LeSabre Custom 1994 - HARD FAILURES

Hard failures cause SERVICE ENGINE SOON light to glow and remain on until malfunction is repaired. If light comes on and remains on (light may flash) during vehicle operation, cause of malfunction must be determined using diagnostic (code) charts. If a sensor fails, control module will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional, but it will most likely encounter degraded driveability.

Buick LeSabre Custom 1994 - INTERMITTENT FAILURES

Intermittent failures cause SERVICE ENGINE SOON light to flicker or glow and go out about 10 seconds after intermittent fault goes away. Corresponding trouble code, however, will be retained in control module memory. If related fault does not reoccur within 50 engine starts, related trouble code will be erased from control module memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See INTERMITTENTS in TESTS W/O CODES article in this section.

Buick LeSabre Custom 1994 - DIAGNOSTIC PROCEDURE

Diagnosis of computerized engine control system should be performed in following order:

1. Ensure all engine systems not related to computer system are operating properly. DO NOT proceed with testing unless all other problems have been repaired. DIAGNOSTIC CIRCUIT CHECK must be performed before using trouble code charts. See BASIC TESTING article in this section.
2. If trouble codes were displayed (other than Code 12), determine whether codes are hard or intermittent trouble codes. Hard codes will cause SERVICE ENGINE SOON light to glow continuously while engine is running. See HARD OR INTERMITTENT TROUBLE CODE DETERMINATION . For diagnosing hard codes, proceed to appropriate trouble code chart. For diagnosing intermittent codes, proceed to INTERMITTENTS in TESTS W/O CODES article in this section.
3. If no trouble codes are present and a driveability problem exists, refer to SYMPTOMS in TESTS W/O CODES article in this section. Doing so will help identify proper system or component to check in SYSTEM & COMPONENT TESTS article in this section.
4. After necessary repairs are made, clear trouble codes and perform FIELD SERVICE MODE CHECK in BASIC TESTING article in this section.

NOTE:

For information on retrieving codes using a scan tester, refer to user and reference manuals supplied with tester.

Buick LeSabre Custom 1994 - RETRIEVING CODES (NON-SCAN)

NOTE:

On models using a 12-terminal DLC (previously referred to as the ALDL), if a wire is present at terminal "B", inserting a jumper wire into test and ground terminals of DLC with engine running will cause fuel injected vehicles to enter field service mode. Flashes of SERVICE ENGINE SOON light will not indicate codes if this is done. See FIELD SERVICE MODE CHECK in BASIC TESTING article in this section. On models not using a 12-terminal DLC or not having a wire present in terminal "B", codes must be retrieved using a hand-held scan tester.

Buick LeSabre Custom 1994 DATA LINK CONNECTOR (DLC) TEST TERMINALS

Application	Ground/Test
16-Pin DLC	(1)
(1) Tech 1 scan tester required to activate output/field service mode.

1. Turn ignition on. DO NOT start engine. SERVICE ENGINE SOON light should glow. Locate DLC attached to control module wiring harness. Most DLC's are located under dash on driver side of vehicle. For exact location of DLC, proceed to COMPONENT LOCATIONS in the SYSTEM & COMPONENT TESTS article in this section. Insert jumper wire from terminal "B" (diagnostic test terminal) to terminal "A" (ground) of DLC. See Fig. 1 .
2. SERVICE ENGINE SOON light should begin to flash codes. Each code will be repeated 3 times. If codes are not flashed or SERVICE ENGINE SOON light does not glow, perform DIAGNOSTIC CIRCUIT CHECK in BASIC TESTING article in this section. To exit diagnostic mode, turn ignition off and remove jumper wire from DLC connector.

Fig. 1: Buick LeSabre Custom 1994 - Component Locations - ALDL/DLC Connector Terminal ID

Buick LeSabre Custom 1994 - READING TROUBLE CODES

Control module stores component failure information under a related trouble code which can be recalled for diagnosis and repair. Trouble codes may be read by counting flashes of SERVICE ENGINE SOON light or by reading digital display on a scan tester. Scan tester is faster to use, more accurate and capable of reading information which otherwise would necessitate testing individual control module and sensor/solenoid connector terminals using a digital voltmeter. See SCAN TESTER USAGE and SCAN DATA .

NOTE:

When using most scan testers, a time delay exists between serial data updates. For instantaneous response, a digital voltmeter must be used.

If scan tester is not available, reading flashes of SERVICE ENGINE SOON light is possible by grounding diagnostic test terminal "B" (if a wire is present) of DLC with ignition on and engine off. See Fig. 1 . For example, "FLASH, FLASH, pause, FLASH, longer pause "identifies Code 21. First series of flashes is first digit of trouble code. Second series of flashes is second digit of trouble code. Trouble codes are displayed starting with lowest numbered code. Each code is displayed 3 times. Codes will continue to repeat as long as DLC test terminal is grounded.

NOTE:

Trouble codes will be recorded at various operating times. Some codes require operation of that sensor or switch for 5 seconds; others require operation for 5 minutes or longer at normal operating temperature, vehicle speed and load. Therefore, some codes may not set in a service bay operational mode and may require road testing vehicle in order to duplicate condition under which code will set.

Buick LeSabre Custom 1994 - TROUBLE CODE DEFINITION

Buick LeSabre Custom 1994 PCM TROUBLE CODE CONVERSION ⁽¹⁾

New No.	Old No.	Circuit
P0101	34	MAF Sensor
P0112	23	Air Temperature Sensor
P0113	25	Air Temperature Sensor
P0117	15	Coolant Temperature Sensor
P0118	14	Coolant Temperature Sensor
P0122	22	Throttle Position Sensor
P0123	21	Throttle Position Sensor
P0125	New	Coolant Temperature Sensor
P0131	44	Oxygen Sensor
P0132	45	Oxygen Sensor
P0134	13	Oxygen Sensor
P0137	New	(Catalyst) Oxygen Sensor
P0138	New	(Catalyst) Oxygen Sensor
P0140	New	(Catalyst) Oxygen Sensor
P0171	New	Fuel Lean
P0172	New	Fuel Rich
P0300	New	Misfire
P0321	17	Spark Reference
P0325	43	Knock Sensor
P0341	18	Cam Signal
P0342	41	Cam Signal
P0401	53/54/55	EGR
P0420	New	Catalyst System
P0501/0502	24	Vehicle Speed Sensor
P0703	38	TCC Brake Switch
P0705	31	Trans. Range Switch
P0712	New	Trans. Fluid Temp. Sensor
P0713	New	Trans. Fluid Temp. Sensor
P0740	39	TCC
P0755	36	Shift Solenoid "B"
P1257	57	Supercharger Boost
P1350/1361	42	Ignition
P1403/1404/1405	75/76/77	EGR Solenoid(s)
P1406	New	EGR
P1530	69	A/C Pressure Switch
P1531	66	A/C Charge Low
P1550	New	Cruise
P1558	63	Cruise
P1561	61	Cruise
P1562	62	Cruise
P1565	65	Cruise
P1567	67	Cruise
P1568	68	Cruise
P1571	New	Traction Control
P1573	New	Traction Control
P1599	99	Cruise
P1619	New	Oil Life Reset
P1623	51	PROM Error
P1626/1629	58	Pass-Key
P1630	16	Voltage High/Low
P1640	26/56	Quad-Driver
P1650	26/56	Quad-Driver
P1670	26/56	Quad-Driver
(1) All P0 and P1 codes are located at the end of the pre-existing code charts.

NOTE:

Use trouble code charts only if SERVICE ENGINE SOON light is illuminated (indicating a current problem exists).

Buick LeSabre Custom 1994 - HARD OR INTERMITTENT TROUBLE CODE DETERMINATION

During any diagnostic procedure, determine if codes are hard failure codes or intermittent failure codes. Diagnostic charts will not usually help analyze intermittent codes. To determine hard codes and intermittent codes:

1. Enter diagnostic mode. Read and record all stored trouble codes. Exit diagnostic mode, and clear trouble codes. See CLEARING TROUBLE CODES .
2. Apply parking brake, and place transmission in Neutral or Park. Block drive wheels, and start engine. SERVICE ENGINE SOON light should go out. Run warm engine at specified curb idle for 2 minutes and note SERVICE ENGINE SOON light.
3. If SERVICE ENGINE SOON light comes on, enter diagnostic mode. Read and record trouble codes. This will reveal hard failure codes. Oxygen sensor related codes may require a road test to reset hard failure after trouble codes were cleared.
4. If SERVICE ENGINE SOON light does not come on, all stored trouble codes were intermittent failures, except as noted above.

Buick LeSabre Custom 1994 - CLEARING TROUBLE CODES

NOTE:

On models not utilizing a 12-terminal DLC or if no wire is present in terminal "B", codes are cleared using a scan tester.

Turn ignition switch to ON position, and ground diagnostic test terminal "B" at DLC. See Fig. 1 . Turn ignition switch to OFF position, and remove control module fuse from fuse block for 10 seconds. Replace fuse. Remove diagnostic terminal ground lead. If fuse cannot be located, pigtail at battery can be disconnected. When power to ECM is remove, degraded driveability may be exhibited until control module "relearns" optimum operational parameters.

Buick LeSabre Custom 1994 - ECM/PCM LOCATION

On most models, engine control module is located behind right or left side of dash or behind right or left kick panel. See COMPONENT LOCATIONS in SYSTEM & COMPONENT TESTS article in this section.

Buick LeSabre Custom 1994 - DIAGNOSTIC MATERIALS Diagnostic Aids

Diagnostic aids (located in many trouble code charts) are additional tips used to help diagnose trouble codes when inspected circuit is okay. Diagnostic aids may help lead to a definitive solution to trouble code problem.

Buick LeSabre Custom 1994 - Field Service Mode Check (If Available)

If DLC test terminal "B" is grounded with engine running, SERVICE ENGINE SOON light will indicate operational mode of engine. This test confirms proper operation of fuel system and verifies "closed loop" operation. Clear codes and perform this test after any repair is completed. Some models require the use of a scan tester to enter field service mode. Field service mode check can be found by proceeding to FIELD SERVICE MODE CHECK in BASIC TESTING article in this section.

Buick LeSabre Custom 1994 - SPECIAL TOOLS (DIAGNOSTIC)

NOTE:

A scan tester plugged into DLC may be used to read trouble codes and check voltages in system on serial data line (terminal "E", or terminal "M"). This can save a great deal of time. For additional information, see SCAN TESTER USAGE and SCAN DATA .

Computerized engine control system is most easily diagnosed using scan tester; however, other tools may aid in diagnosing problems if a scan tester is unavailable. These tools are a tachometer, test light, ohmmeter, digital voltmeter with 10-megohm input impedance (minimum), vacuum pump, vacuum gauge, fuel injector test lights and 6 jumper wires 6" long (one wire with female connectors at both ends, one wire with male connectors at both ends and 4 wires with male and female connectors at opposite ends). A test light, rather than a voltmeter, must be used when indicated by a diagnostic chart.

Buick LeSabre Custom 1994 - SCAN TESTER USAGE

NOTE:

Before connecting scan tester to vehicle, diagnostic system should be checked to determine if system is operating properly and if information received will be accurate. This is done by performing DIAGNOSTIC CIRCUIT CHECK located in the BASIC TESTING article in this section. If vehicle does not pass diagnostic circuit check, information received may be invalid.

Scan tester is a specialized tester which, when plugged into DLC, can be used to diagnose on-board computer control systems by providing instant access to circuit voltage information without need to crawl under dash or hood to backprobe sensors and connectors.

Scan tester cuts down diagnostic time dramatically by furnishing input data (voltage signals) which can be compared to specification parameters. See SCAN DATA . They may also furnish information on output device (solenoids and motors) status. However, status parameters only indicate output signals have been sent to devices by control module; they do not indicate whether devices have responded properly to signal. Verify proper response at output device using a voltmeter or test light. Vehicles utilizing a 16-terminal DLC or 12-terminal DLC with terminal "B" not used, must use a scan tester for retrieving codes or enter Field Service Mode.

NOTE:

Code 12 should always exist when DLC terminal "B" is grounded with key on and engine not running, but it may not be indicated by all makes of scan testers.

A problem may exist even if trouble codes are not present. About 80 percent of driveability problems occur without trouble codes. Sensors that are out of calibration will not set a trouble code but will cause driveability problems.

Using a scan tester is the easiest method of checking sensor specifications and other data parameters. Tester is also useful in finding intermittent wiring problems by wiggling wiring harnesses and connections (key on, engine off) while observing data parameters. See SCAN DATA .

NOTE:

If erroneous voltage signals are suspected, verify tester information using a digital voltmeter and wiring schematic. If non-existent codes are displayed, turn ignition off, remove tester, turn ignition on and ground DLC test terminal "B". Same codes flashed by SERVICE ENGINE SOON light should be indicated by scan tester.

Buick LeSabre Custom 1994 - SCAN DATA

NOTE:

Information contained in following tables is typical of readings taken on vehicle with engine idling, upper radiator hose hot, closed throttle, transmission in Park or Neutral, "closed loop" status achieved and all accessories off (except as noted in tables). Data parameters are updated a minimum of every 1 1/4 seconds. On systems using P-4 computers, parameter updates are more frequent. Not all devices and systems are used on all models; following lists only represent most commonly used parameters. For additional information, refer to owner manual furnished with tester.

Buick LeSabre Custom 1994 MULTIPORT FUEL INJECTION (MFI)

Tester Position	Units Measured	Nominal Value
A/C Clutch	On/Off	Off (On With A/C)
A/C Request	Yes/No	No/Yes (With Request)
AIR Divert Sol.	On/Off	On (Air To Switching Sol.); Off (Air To Atmosphere)
AIR Switching Sol.	On/Off	On (To Exhaust Manifold); Off (To Catalytic Converter)
BARO	Volts	3.0-4.5
Battery Voltage	Volts	13.5-14.5
Block Learn (LT)	Counts	118-138 (128 Normal)
Canister Purge Sol.	On/Off	On/Engine Cold (Idle Some)
Clear Flood	On/Off	See Tester Manual
Coolant Fan(s)	On/Off	Off Below 216?F (102?C)
Coolant Temp.	?C	85-105? (Norm. Temp.)
Crank RPM	RPM	100-900
Cross Counts	Counts	0-255
EGR Solenoid	On/Off	On When Energized
EGR Duty Cycle	0-100%	0/Closed; 100/Fully Open
Fan Relay	On/Off	On When Energized
Fan Request	On/Off	On With Request
Fuel Back-Up	Yes/No	Yes When Engaged
IAC	Counts	0-50
Ignition/Crank	On/Off	On With Ignition/Crank
Injector Pulse Width	Mil./Sec	.8-3.0
Integrator (ST)	Counts	110-145 (128 Normal)
Knock Retard	Counts	0-255
Knock Signal	Yes/No	Yes When Knock Exists
MAT (IAT)	?C	10-90?
MAP	Volts	1.0 (Idle) to 4.5 (WOT)
"Open/Closed Loop Status"	Ol/Cl	Closed/Open During Extended Idle
O2 Sensor	Millivolts	100 (Lean) To 999 (Rich)
P/N Switch	P/N/RDL	Park/Neutral
P/S Switch	Norm/Hi	Normal
PROM I.D.	PROM #	Original Factory Number
RPM	RPM	Spec. +/-25 RPM Drive (A/T); Spec. +/-50 RPM Neut. (M/T)
Spark Advance	Degrees	Varies
TCC	On/Off	Off (On With Command)
TP Sensor	Volts	1.25 (Idle) To 5.00 (WOT)
Throttle Angle	0-100%	0 (Idle) To 100 (WOT)
Trouble Codes	Code No.	No Codes
Upshift Light (M/T)	On/Off	Off
VSS Or MPH	MPH	0-Actual
1st Gear Switch	On/Off	On/1st Gear Only
3rd Gear Switch	On/Off	On/3rd & 4th Gear
4th Gear Switch	On/Off	On/4th Gear

Buick LeSabre Custom 1994 - ECM/PCM CODE CHARTS

NOTE:

In following diagnostic tests, schematics and illustrations are courtesy of General Motors Corp.

Buick LeSabre Custom 1994 - CODE P0101, MAF SENSOR CIRCUIT

The Mass Air Flow (MAF) sensor measures the flow of air which passes through it in a given time. PCM uses this information to monitor the operating condition of the engine for fuel delivery calculations. A large quantity of air movement indicates acceleration, while a small quantity indicates deceleration or idle. MAF sensor produces a frequency signal, which cannot be easily measured. Diagnose sensor using procedures on this chart.

Code P0101 will set when the following conditions are present.

• Engine is running.
• No MAF signal for over 4 seconds.

With Code P0101 set, PCM will use a default value for airflow based on throttle position, IAC motor position and engine speed. PCM will illuminate Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. This step checks to see if PCM recognizes a problem.
2. Voltage reading at sensor harness terminal "A" of less than 4 volts or greater than 6 volts indicates a fault in circuit No. 492 (Yellow wire), or poor connection.
3. Verifies that both ignition feed voltage and a good ground circuit are available.

Buick LeSabre Custom 1994 - Diagnostic Aids

An intermittent may be caused by a poor connection, mis-routed harness, rubbed through wire insulation or a wire broken inside the insulation. Check for:

• Poor Connection At PCM pin: Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
• Mis-Routed Harness: Inspect MAF sensor harness to ensure it is not too close to high voltage wires, such as spark plug wires.
• Damaged Harness: Inspect harness for damage. If harness appears okay, observe Tech-1 while moving related connectors and wiring harness. A change in display would indicate intermittent fault location.
• Plugged Air Intake Filter: A wide-open throttle acceleration from a stop should cause MAF reading on Tech-1 to range from approximately 4-7 grams per second at idle to 100 or greater at time of 1-2 shift. If not, check for restriction.

Fig. 2: Buick LeSabre Custom 1994 - Component Locations - Code P0101 Schematic (3.8L) MAF Sensor Circuit

Fig. 3: Buick LeSabre Custom 1994 - Component Locations - Code P0101 Flow Chart (3.8L) MAF Sensor Circuit

Buick LeSabre Custom 1994 - CODE P0112, IAT SENSOR CIRCUIT (LOW TEMPERATURE INDICATED)

The Intake Air Temperature (IAT) sensor is a thermistor. PCM applies and monitors 5 volts to sensor. When air is cold, sensor resistance is high and PCM will measure a high signal voltage. If air is warm, sensor resistance is low causing PCM to measure low voltage.

Code P0112 will set when the following conditions are present.

• Engine coolant temperature is greater than 140?F (60?C).
• Mass air flow is less than 12 grams per second.
• Vehicle speed is less than 25 MPH.
• IAT signal voltage indicates an intake air temperature less than -29?F (-34?C) for 5 seconds.

With Code P0112 set, PCM will substitute a default value of 61?F (16?C) for intake air temperature. Code P0112 does not illuminate the Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. An open sensor, wire or connection will cause Code P0112 to set. An open circuit would cause Tech-1 to display approximately -40?F (-40?C). This test determines if wiring and PCM are okay.

Buick LeSabre Custom 1994 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for:

• Poor Connection Or Damaged Harness

Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

• Intermittent Test

Observe IAT on Tech-1 while moving related connectors and wiring harness with warm engine running. If failure is induced, IAT display will change to a -40? temperature reading. This may assist in isolating the location of the malfunction.

Fig. 4: Buick LeSabre Custom 1994 - Component Locations - Code P0112 Schematic (3.8L) IAT Sensor Circuit (Low Temperature Indicated)

Fig. 5: Buick LeSabre Custom 1994 - Component Locations - Code PO112 Flow Chart (3.8L) IAT Sensor Circuit (Low Temperature Indicated)

Buick LeSabre Custom 1994 - CODE P0113, IAT SENSOR CIRCUIT (HIGH TEMPERATURE INDICATED)

The Intake Air Temperature (IAT) sensor is a thermistor. PCM applies and monitors 5 volts on circuit to sensor. When air is cold, sensor resistance is high and PCM will measure a high signal voltage. If air is warm, sensor resistance is low causing PCM to measure low voltage.

Code P0113 will set when the following conditions are present.

• Signal voltage indicates an intake air temperature greater than 284?F (140?C).
• Vehicle speed is greater than 35 MPH.
• Above conditions are met for at least for 5 seconds.

With Code P0113 set, PCM will use a default value of 61?F (16?C) for intake air temperature. Code P0113 does not illuminate the Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. Tech-1 may be used to diagnose this fault since PCM transmits actual values when the fault is present. A grounded circuit will cause Tech-1 to display a temperature of approximately 297?F (147?C).
2. If Tech-1 displays -40? with IAT sensor disconnected, PCM and wiring are okay. Replace IAT sensor.

Buick LeSabre Custom 1994 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for:

• Poor Connection Or Damaged Harness: Inspect PCM harness for short to ground in circuit No. 472 (Tan wire), improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.
• Intermittent Test: Observe IAT on Tech-1 while moving related connectors and wiring harness with warm engine running. If failure is induced, IAT display will change to a 297?F (147?C) temperature reading. This may assist in isolating the location of the malfunction.

Fig. 6: Buick LeSabre Custom 1994 - Component Locations - Code P0113 Schematic (3.8L) IAT Sensor Circuit (High Temperature Indicated)

Fig. 7: Buick LeSabre Custom 1994 - Component Locations - Code P0113 Flow Chart (3.8L) IAT Sensor Circuit (High Temperature Indicated)

Buick LeSabre Custom 1994 - CODE P0117, COOLANT TEMP SENSOR LOW TEMP INDICATED

ECT sensor uses a thermistor to control signal voltage to PCM. PCM applies and monitors a 5 volts to ECT sensor. When engine coolant is cold, sensor (thermistor) resistance is high and PCM will sense a high signal voltage. As engine coolant warms up, sensor resistance becomes less and PCM voltage drops. With Code P0117 set, PCM will turn cooling fans on and use a default engine coolant temperature value based on run time. PCM will illuminate Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. Code 14 reference applies to 5.7L only. This step determines if conditions necessary to set Code P0117 exist.
2. Determines if circuit is shorted to ground.

Buick LeSabre Custom 1994 - Diagnostic Aids

Tech 1 displays engine temperature in degrees celsius (?C) and fahrenheit (?F). After engine is started, temperature should rise steadily to 194?F (90?C), then stabilize when thermostat opens. An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for:

• Poor Connection Or Damaged Harness: Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.
• Intermittent Test: Using Tech 1, monitor engine coolant temperature while moving related connectors and wiring harness. If failure is induced, display will change. This may assist in isolating the location of the malfunction.
• Shifted Sensor: See TEMPERATURE-TO-RESISTANCE VALUES table to test ECT sensor at various temperature levels to evaluate the possibility of a shifted (mis-scaled) sensor which may result in driveability complaints.
• A faulty connection, or an open in sensor circuits will cause Code P0117 to set.

Buick LeSabre Custom 1994 TEMPERATURE-TO-RESISTANCE VALUES ⁽¹⁾

Temperature ?F (?C)	Ohms
212 (100)	177
194 (90)	241
158 (70)	467
104 (40)	1459
68 (20)	3520
23 (-5)	12,300
14 (-10)	16,180
0 (-18)	25,000
-4 (-20)	28,680
-22 (-30)	52,700
-40 (-40)	100,700
(1) Measure resistance across sensor terminals.

Fig. 8: Buick LeSabre Custom 1994 - Component Locations - Code P0117 Schematic (3.8L) Coolant Temperature Sensor Low Temperature Indicated

Fig. 9: Buick LeSabre Custom 1994 - Component Locations - Code P0117 Flow Chart (3.8L) Coolant Temperature Sensor Low Temperature Indicated

Buick LeSabre Custom 1994 - CODE P0118, COOLANT TEMP SENSOR HIGH TEMPERATURE INDICATED

ECT sensor uses a thermistor to control signal voltage to PCM. PCM applies and monitors a 5 volts to ECT sensor. When engine coolant is cold, sensor (thermistor) resistance is high and PCM will sense a high signal voltage. As engine coolant warms up, sensor resistance becomes less and PCM voltage drops. With Code P0118 set, PCM will turn cooling fans on and use a default engine coolant temperature value based on run time. PCM will illuminate Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. Code 15 reference applies to 5.7L only. This step determines if conditions necessary to set Code P0118 exist.
2. This test will determine if signal circuit is shorted to ground which will cause conditions for Code P0118.
3. This test will determine if circuit is open. If circuits are okay, check connections at PCM and ECT sensor.

Buick LeSabre Custom 1994 - Diagnostic Aids

Tech 1 displays engine temperature in degrees celsius (?C) and fahrenheit (?F). After engine is started, temperature should rise steadily to 194?F (90?C), then stabilize when thermostat opens. An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check the following for:

• A short to ground in circuit No. 410 (Yellow wire).
• Intermittent Test: Using Tech 1, monitor engine coolant temperature while moving related connectors and wiring harness. If failure is induced, display will change. This may assist in isolating the location of the malfunction.
• Shifted Sensor: See TEMPERATURE-TO-RESISTANCE VALUES table to test ECT sensor at various temperature levels to evaluate the possibility of a shifted (mis-scaled) sensor which may result in driveability complaints.

Buick LeSabre Custom 1994 TEMPERATURE-TO-RESISTANCE VALUES ⁽¹⁾

Temperature ?F (?C)	Ohms
212 (100)	177
194 (90)	241
158 (70)	467
104 (40)	1459
68 (20)	3520
23 (-5)	12,300
14 (-10)	16,180
0 (-18)	25,000
-4 (-20)	28,680
-22 (-30)	52,700
-40 (-40)	100,700
(1) Measure resistance across sensor terminals.

Fig. 10: Buick LeSabre Custom 1994 - Component Locations - Code P0118 Schematic (3.8L) Coolant Temperature Sensor High Temperature Indicated

Fig. 11: Buick LeSabre Custom 1994 - Component Locations - Code P0118 Flow Chart (3.8L) Coolant Temperature Sensor High Temperature Indicated

Buick LeSabre Custom 1994 - CODE P0122, THROTTLE POSITION SENSOR SIGNAL VOLTAGE LOW

The Throttle Position (TP) sensor provides a voltage signal that changes relative to throttle blade angle. Signal voltage will vary from .20-.74 volt at idle to greater than 4 volts at Wide Open Throttle (WOT). TP sensor signal is one of the most important inputs used by PCM for fuel control and for most of the PCM control outputs.

Code P0122 will set when the following conditions are present.

• Ignition on.
• TP sensor signal voltage is less than .2 volt for a precalibrated time.

With Code P0122 set, Tech 1 will continue to display the actual throttle sensor voltage, but ignore TP signal and read mass air flow value for other PCM controlled functions, PCM will not allow 4th gear, TCC or cruise control operation, 1st, 2nd, and 3rd allowed. PCM will illuminate Malfunction Indicator Light (MIL).

If signal circuit is open or grounded when engine is started, a high idle may occur. Tech 1 may read as follows with signal open or grounded.

• TP equals .2 volt or less.
• MIL is illuminated.
• Code P0122 is set.

  NOTE:

  Test numbers refer to numbers on diagnostic chart.

1. Determines if conditions necessary to set Code P0122 exist.
2. Simulates Code P0123 (high voltage). If PCM recognizes high signal voltage and sets Code P0123, PCM and wiring are okay.
3. Simulates a high signal voltage. Checks signal circuit for an open.

Buick LeSabre Custom 1994 - Diagnostic Aids

Tech 1 displays throttle position in volts. Voltage should increase steadily as throttle is moved toward WOT.

An open or short to ground in reference and signal circuits will cause Code P0122 to set. Check for:

• Poor Connection Or Damaged Harness: Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.
• Intermittent Test: Monitor TP sensor voltage display on Tech 1 while moving related connectors and wiring harness. If failure is induced, display will change. This may assist in isolating the location of the malfunction.
• TP Sensor Scaling: Observe TP sensor voltage display while depressing accelerator pedal with engine stopped and ignition
  1. Display should vary from closed throttle TP sensor voltage when throttle is closed (.20-.74 volt) to greater than 4 volts when throttle is held at WOT position.

Fig. 12: Buick LeSabre Custom 1994 - Component Locations - Code P0122 Schematic (3.8L) Throttle Position Sensor Signal Voltage Low

Fig. 13: Buick LeSabre Custom 1994 - Component Locations - Code P0122 Flow Chart (3.8L) Throttle Position Sensor Signal Voltage Low

Buick LeSabre Custom 1994 - CODE P0123, THROTTLE POSITION SENSOR SIGNAL VOLTAGE HIGH

The Throttle Position (TP) sensor provides a voltage signal that changes relative to throttle blade angle. Signal voltage will vary from .20-.74 volt at idle to approximately 5 volts at Wide Open Throttle (WOT). TP sensor signal is one of the most important inputs used by PCM for fuel control and for most of the PCM control outputs.

Code P0123 will set when the following conditions are present.

• TP sensor voltage is greater than 4.8 volts at any time, or engine is running and air flow is less than 17 grams per second.
• Engine speed is greater than 600 RPM.
• TP sensor signal voltage is greater than 1.06 volts.
• Code P0101 is not present.
• All conditions are met for 5 seconds.

With Code P0123 set, Tech 1 will continue to display the actual throttle sensor voltage, but ignore TP signal and read mass air flow value for other PCM controlled functions, PCM will not allow 4th gear, TCC or cruise control operation, 1st, 2nd, and 3rd allowed. PCM will illuminate Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. With closed throttle, ignition on, or at idle, voltage at PCM TP sensor signal circuit should be .20-.74 volt.
2. With TP sensor disconnected, TP sensor voltage should decrease and Code P0122 will set. This test verifies that PCM and wiring are okay.
3. Probing ground circuit with a test light check sensor ground circuit. A faulty sensor ground circuit will cause Code P0123 to set.

Buick LeSabre Custom 1994 - Diagnostic Aids

Tech 1 displays throttle position in volts. With closed throttle, ignition on, or at idle, voltage should be .20-.74 volt. If voltage is not as specified, replace TP sensor. An open in sensor ground circuit will cause Codes P0112, P0712, P0117 and P0123 to set. Check for:

• Poor Connection Or Damaged Harness: Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.
• Intermittent Test: Monitor TP sensor voltage display on Tech 1 while moving related connectors and wiring harness. If failure is induced, display will change. This may assist in isolating the location of the malfunction.
• TP Sensor Scaling: Observe TP sensor voltage display while depressing accelerator pedal with engine stopped and ignition
  1. Display should vary from closed throttle TP sensor voltage when throttle is closed (.20-.74 volt) to greater than 4 volts when throttle is held at WOT position.

Fig. 14: Buick LeSabre Custom 1994 - Component Locations - Code P0123 Schematic (3.8L) Throttle Position Sensor Signal Voltage High

Fig. 15: Buick LeSabre Custom 1994 - Component Locations - Code P0123 Flow Chart (3.8L) Throttle Position Sensor Signal Voltage High

Fig. 16: Buick LeSabre Custom 1994 - Component Locations - Code P0123 Flow Chart

Buick LeSabre Custom 1994 - CODE P0131, HEATED OXYGEN SENSOR LOW SIGNAL VOLTAGE (LEAN)

The PCM supplies and monitors a voltage of approximately .45 volt between PCM HO2S low reference circuit and HO2S signal circuit. If read with a 10-megohm DVOM, voltage may read as low as .32 volt. HO2S varies voltage within a range of approximately 1.0 volt (rich) to .10 volt (lean). Sensor is like an open circuit and produces no voltage when less than approximately 600?F (360?C). Open loop operation is caused by Codes P0131 or P0132, an open sensor circuit, or a cold sensor. Code P0131 will set when the following conditions are present.

• HO2S signal voltage remains less than .248 volt for at least 4.2 minutes.
• System is operating in closed loop.

Code P0131 will cause system to operate in open loop. PCM will illuminate Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. Running engine at 1200 RPM keeps oxygen sensor hot to ensure oxygen sensor remains active and can read exhaust oxygen content accurately.
2. Opening HO2S signal circuit and grounding HO2S low circuit should result in a displayed voltage between .35-.55 volt. If display is still fixed less than .35 volt, fault is a short to ground in signal circuit, or faulty PCM.

Buick LeSabre Custom 1994 - Diagnostic Aids

Using Tech 1, observe LT fuel trim values at different RPM and air flow conditions. Tech 1 also displays fuel trim cells allowing LT fuel trim values to be checked in each cell, determining when Code P0131 may have been set. LT fuel trim values will be around 158 or greater if conditions exist for Code P0131 to set.

• Heated Oxygen Sensor Wire: Sensor pigtail may be mispositioned and contacting exhaust manifold.
• Check for intermittent ground in wire between connector and sensor.
• Poor PCM to engine block ground.
• MAF Sensor: System will go lean when MAF sensor output causes PCM to sense a lower than normal air flow. Disconnect MAF sensor. If lean condition no longer exists, replace MAF sensor.
• Lean Injectors: Perform injector balance test.
• Fuel Contamination: Water near in-tank fuel pump inlet causing fuel contamination in fuel delivered to injectors. Water causes a lean exhaust and can set Code P0131.
• Fuel Pressure: If pressure is too low, system will be lean. To confirm, monitor fuel pressure while driving at various speeds and/or load conditions.
• Exhaust Leaks: If an exhaust leak above the oxygen sensor is present, outside air may be allowed to be pulled into exhaust stream and flow past sensor.
• Vacuum Or Crankcase Leak: Can cause a lean condition and/or possibly a high idle.
• If all above components/systems are okay, heated oxygen sensor is faulty.
• Faulty HO2S Heater or Heater Circuit: Refer DIAGNOSTICS AIDS in Code P0134 chart.

Fig. 17: Buick LeSabre Custom 1994 - Component Locations - Code P0131 Schematic (3.8L) Heated Oxygen Sensor Low Signal Voltage (Lean)

Fig. 18: Buick LeSabre Custom 1994 - Component Locations - Code P0131 Flow Chart (3.8L) Heated Oxygen Sensor Low Signal Voltage (Lean)

Buick LeSabre Custom 1994 - CODE P0132, HEATED OXYGEN SENSOR HIGH SIGNAL VOLTAGE (RICH)

The PCM supplies and monitors a voltage of approximately .45 volt between PCM HO2S low reference circuit and HO2S signal circuit. If read with a 10-megohm DVOM, voltage may read as low as .32 volt. HO2S varies voltage within a range of approximately 1.0 volt (rich) to .10 volt (lean). Sensor is like an open circuit and produces no voltage when less than approximately 600?F (360?C). Open loop operation is caused by Codes P0131, P0132 or P0134, or a cold sensor.

Code P0132 will set when the following conditions are present.

• HO2S voltage on signal circuit remains greater than .75 volt for at least 2 minutes while in closed loop.
• Throttle angle is between 6-40 percent.
• Codes P0122 or P0123 are not set.

Code P0132 will cause system to operate in open loop. PCM will illuminate Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. Determines if conditions necessary to set Code P0132 exist
2. When grounding circuits, Tech 1 should read less than .35 volt. If display is not as specified, check for short to voltage in signal circuit.

Buick LeSabre Custom 1994 - Diagnostic Aids

• Fuel Pressure: If pressure is too high, system will be rich. PCM can compensate for some increase. However, Code P0132 will set if pressure gets too high.
• Rich Injectors: Perform injector balance test.
• Leaking Injectors: Check for fuel contaminated oil.
• EVAP Canister Purge: Check for fuel saturation. If full of fuel, check canister control and hoses.
• MAF Sensor: System will go rich when MAF sensor output causes PCM to sense a higher than normal air flow. Disconnecting MAF sensor will allow PCM to set a fixed value for sensor. If rich condition no longer exists, replace MAF sensor.
• Check for leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for fuel.
• TP Sensor: An intermittent TP sensor output will cause system to go rich due to a false indication of throttle moving.
• False rich indication due to silicon contamination of heated oxygen sensor. This will be indicated by Code P0131 accompanied by lean driveability conditions and a powdery White deposit on sensor.
• Heated Oxygen Sensor (HO2S): If HO2S is internally shorted, HO2S voltage displayed on Tech 1 will be greater than 1 volt. Disconnect HO2S with ignition on and engine running. If displayed voltage decreases from greater than 1.0 volt to approximately .45 volt, replace HO2S.
• Faulty HO2S Heater Or Heater Circuit: Refer DIAGNOSTICS AIDS in Code P0134 chart.

Fig. 19: Buick LeSabre Custom 1994 - Component Locations - Code P0132 Schematic (3.8L) Heated Oxygen Sensor High Signal Voltage (Rich)

Fig. 20: Buick LeSabre Custom 1994 - Component Locations - Code P0132 Flow Chart (3.8L) Heated Oxygen Sensor High Signal Voltage (Rich)

Buick LeSabre Custom 1994 - CODE P0134, HEATED OXYGEN SENSOR OPEN CIRCUIT

The PCM supplies and monitors voltage of approximately .45 volt between PCM HO2S low reference circuit (Tan wire) and HO2S signal circuit (Purple wire). If read with a 10 megohm DVOM, voltage may read as low as .32 volt. HO2S varies voltage within a range of approximately 1 volt (rich) to .10 volt (lean). Sensor is like an open circuit and produces no voltage when less than approximately 600?F (360?C). Open loop operation is caused by open oxygen sensor circuit or a cold sensor. Code P0134 will set when the following conditions are present.

• Engine coolant temperature is greater than 110?F (43?C).
• Engine run time is more than 40 seconds.
• HO2S signal voltage is steady between .35-.56 volt.
• Throttle angle is greater than 3 percent.
• All conditions are met for approximately 30 or more seconds.

Code P0134 will cause system to operate in open loop. PCM will illuminate Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. If conditions necessary to set Code P0132 exist, system will not go into closed loop.
2. This will determine if sensor or wiring is cause of Code P0134.
3. This test checks continuity in reference circuit.

Buick LeSabre Custom 1994 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for:

• Poor Connection Or Damaged Harness: Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.
• Faulty HO2S Heater Or Heater Circuit: With ignition on and engine off, HO2S voltage displayed on Tech 1 should gradually decrease to less than .25 volt, indicating heater is functioning properly. If display does not read as specified, disconnect HO2S and connect test light between terminals "C" and "D". If test light does not light, repair open in suspect wire. If test light lights, replace HO2S.
• Intermittent Test: Using Tech 1, monitor HO2S signal voltage while moving related connectors and wiring harness with engine running at part throttle in closed loop. If failure is induced, HO2S signal voltage reading will change from normal fluctuating voltage (greater than .6 volt and less than .30 volt) to a fixed value of approximately .45 volt. This may assist in isolating the location of the malfunction.

Fig. 21: Buick LeSabre Custom 1994 - Component Locations - Code P0134 Schematic (3.8L) Heated Oxygen Sensor Open Circuit

Fig. 22: Buick LeSabre Custom 1994 - Component Locations - Code P0134 Flow Chart (3.8L) Heated Oxygen Sensor Open Circuit

Buick LeSabre Custom 1994 - CODE P0171, FUEL TRIM LEAN

A closed loop air/fuel metering system is used to provide the best possible combination of driveability, fuel economy and emission control. While in closed loop, PCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. The Tech 1 monitors fuel trim values, and will indicate a change made to fuel delivery by the long and short term fuel trim values.

Ideal fuel trim values are approximately 128. If oxygen sensor signal indicates a lean condition, the PCM will add fuel, resulting in a fuel trim value greater than 128. If a rich condition is detected, fuel trim values will be less than 128, indicating that the PCM is reducing the amount of fuel delivered. PCM will set Code P0171 if an excessively lean condition is detected. Code P0171 will set when the following conditions are present.

• Codes P0101, P0117, P0118, P0122, P0123, P0134, P0501 and P0502 are not set.
• Engine coolant temperature is between 176?F (80?C) and 230?F (110?C).
• Steady throttle less than 91 percent.
• Vehicle speed is less than 70 MPH.
• On VIN L, engine RPM is between 1000-4000 RPM, or on VIN 1, engine RPM is 0-4000 RPM.
• EVAP canister purge duty cycle is less than 80 percent.
• Long term fuel trim is greater than 158.
• Short term fuel trim is 180.
• Above conditions for more than 25 seconds.

When Code P0171 sets, a software flag indicating an emissions related fault will set for 3 trips, after which flag will clear, provided lean condition no longer exists. PCM will illuminate Malfunction Indicator Light (MIL) if conditions necessary for Code P0171 are detected during a trip while flag is set. MIL will remain illuminated for all subsequent trips until code has been cleared or lean condition has not been detected, and conditions for checking fuel trim have been met for 3 consecutive trips.

NOTE:

To complete a trip cycle for fuel trim diagnostic, fuel trim diagnostic test must be enabled and run according to conditions required to set Code P0171. A trip is not considered complete until fuel trim diagnostic has been run by PCM.

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. Visually/physically checking components/systems which may cause a lean condition may determine cause of Code P0171.
2. MAF sensor which causes PCM to read a lower then actual airflow can cause a lean condition, and Code P0171 to set.
3. Check for faults in EVAP purge system that may cause Code P0171 to set.

Buick LeSabre Custom 1994 - Diagnostic Aids

If problem can not be isolated using diagnostic charts, monitor LT fuel trim and fuel trim cell while operating vehicle under various loads. This may isolate condition which caused Code P0171 to set.

A condition that causes Code P0300 (MISFIRE DETECTED) may also set Code P0171. On the other hand, an extremely lean condition which sets Code P0171 can cause a misfire at idle and Code P0300 to set. If cause of Code P0171 can not be determined and Code P0300 is also set, refer to Code P0300 chart.

Fig. 23: Buick LeSabre Custom 1994 - Component Locations - Code P0171 Schematic (3.8L) Fuel Trim Lean

Fig. 24: Buick LeSabre Custom 1994 - Component Locations - Code P0171 Flow Chart (3.8L - 1 Of 2) Fuel Trim Lean

Fig. 25: Buick LeSabre Custom 1994 - Component Locations - Code P0171 Flow Chart (3.8L - 2 Of 2) Fuel Trim Lean

Buick LeSabre Custom 1994 - CODE P0172, FUEL TRIM RICH

A closed loop air/fuel metering system is used to provide the best possible combination of driveability, fuel economy and emission control. While in closed loop, PCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. The Tech 1 monitors fuel trim values, and will indicate a change made to fuel delivery by the long and short term fuel trim values.

Ideal fuel trim values are approximately 128. If oxygen sensor signal indicates a lean condition, the PCM will add fuel, resulting in a fuel trim value greater than 128. If a rich condition is detected, fuel trim values will be less than 128, indicating that the PCM is reducing the amount of fuel delivered. PCM will set Code P0172 if an excessively rich condition is detected. Code P0172 will set when the following conditions are present.

• Codes P0101, P0117, P0118, P0122, P0123, P0501 and P0502 are not set.
• Engine coolant temperature is between 176?F (80?C) and 230?F (110?C).
• Steady throttle less than 91 percent.
• Vehicle speed is less than 70 MPH.
• On VIN L, engine RPM is 1000-4000 RPM, or on VIN 1, engine RPM 0-4000 RPM.
• EVAP canister purge duty cycle is less than 80 percent.
• Long term fuel trim is less than 100.
• Short term fuel trim is less than 94.
• Above conditions exist for more than 25 seconds.

When Code P0172 sets, a software flag indicating an emissions related fault will set for 3 trips, after which flag will clear, provided rich condition no longer exists. PCM will illuminate Malfunction Indicator Light (MIL) if conditions necessary for Code P0172 are detected during a trip while flag is set. MIL will remain illuminated for all subsequent trips until code has been cleared or rich condition has not been detected, and conditions for checking fuel trim have been met for 3 consecutive trips.

NOTE:

To complete a trip cycle for fuel trim diagnostic, fuel trim diagnostic test must be enabled and run according to conditions required to set Code P0172. A trip is not considered complete until fuel trim diagnostic has been run by PCM.

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. Visually/physically checking components/systems which may cause a rich condition may determine cause of Code P0172.
2. MAF sensor which causes PCM to read a higher then actual airflow can cause a rich condition, and Code P0172 to set.
3. Silicon contamination of Heated Oxygen Sensor HO2S can cause a false rich indication that will be sensed by PCM. PCM will then reduce amount of fuel delivered, possibly causing severe driveability symptoms.

Buick LeSabre Custom 1994 - Diagnostic Aids

If problem can not be isolated using diagnostic charts, monitor LT fuel trim and fuel trim cell while operating vehicle under various loads. This may isolate condition which caused Code P0172 to set.

Fig. 26: Buick LeSabre Custom 1994 - Component Locations - Code P0172 Schematic (3.8L) Fuel Trim Rich

Fig. 27: Buick LeSabre Custom 1994 - Component Locations - Code P0172 Flow Chart (3.8L 1 Of 2) Fuel Trim Rich

Fig. 28: Buick LeSabre Custom 1994 - Component Locations - Code P0172 Flow Chart (1 of 2)

Fig. 29: Buick LeSabre Custom 1994 - Component Locations - Code P0172 Flow Chart (3.8L - 2 Of 2) Fuel Trim Rich

Fig. 30: Buick LeSabre Custom 1994 - Component Locations - Code P0172 Flow Chart (2 of 2)

Buick LeSabre Custom 1994 - CODE P0321, SPARK REFERENCE CIRCUIT

PCM uses the spark reference signal circuit to improve ignition timing accuracy during crank and at engine speeds up to 1200 RPM. The spark reference circuit allows use of ignition control mode at speeds less than 400 RPM, eliminating the need to utilize module mode during start-up, and also allows PCM to calculate true crankshaft position in 1/6 the time that use of fuel control reference signal would permit.

During normal operation, PCM uses spark reference signal to control ignition timing until engine speed exceeds 1200 RPM, at which time the fuel control reference signal circuit is used. Code P0321 will set when the following conditions are present.

• PCM detects 150 fuel control reference pulses (50 crank revolutions) and no spark reference pulses.
• Engine speed is less than 1200 RPM.
• Engine running.

Fuel reference signal is used by PCM to control ignition timing advance when conditions for setting Code P0321 are present. This condition will cause module mode to be used for ignition timing less than 400 RPM and PCM controlled ignition timing to be degraded less than 1200 RPM. Code P0321 does not illuminate the Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. Verifies short to ground is not present in spark reference circuit, or an open is not present in ignition jumper harness.
2. Ignition control module will ground spark reference signal if a window on harmonic balancer is interfacing with the 18X Hall Effect switch. Starter may have to be bumped several times to obtain a voltage reading.
3. Voltage reading should be lower than that obtained with engine not running, indicating a pulsed reference signal.

Buick LeSabre Custom 1994 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation, or a broken wire inside insulation. Check for:

• Backed out connector terminals or broken down insulation.
• If connections and harness are okay, monitor voltage on spark reference circuit using DVOM while moving related wiring harness and connectors with engine idling. This may assist in isolating the malfunction.

Fig. 31: Buick LeSabre Custom 1994 - Component Locations - Code P0321 Schematic (3.8L) Spark Reference Circuit

Fig. 32: Buick LeSabre Custom 1994 - Component Locations - Code P0321 Flow Chart (3.8L) Spark Reference Circuit

Fig. 33: Buick LeSabre Custom 1994 - Component Locations - Code P0321 Flow Chart

Buick LeSabre Custom 1994 - CODE P0325, KNOCK SENSOR ERROR

Knock sensor is used to detect engine detonation and allow PCM to retard Ignition Control (IC) timing based on signal being received. The circuitry within knock sensor causes PCM's supplied 5 volts signal to be pulled down, so that under a no knock condition circuit would measure approximately 2.5 volts. Knock sensor produces an AC signal which rides on the 2.5 volts DC voltage. Amplitude and signal frequency is dependent upon the knock level.

If circuit becomes open or shorted to ground, voltage will either become greater than 3.5 volts or less than 1.5 volts. Code P0325 will set if either one of these conditions are present for 20 seconds.

Code P0325 will set when the following conditions are present.

• Voltage on signal circuit becomes greater than 3.5 volts or less than 1.5 volts.
• Either condition is present for 20 seconds.

With Code P0325 set, PCM will illuminate Malfunction Indicator Light (MIL) for remainder of the key cycle and retard spark timing (knock retard) by 10 degrees.

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. If Code P0325 is detected, PCM will retard spark timing by 10 degrees. If an audible is heard from engine, repair internal engine problem. Normally no knock should be detected at idle.
2. PCM applies 5 volts through a pull-up resistor which should be present at knock sensor terminal.

Buick LeSabre Custom 1994 - Diagnostic Aids

Check signal circuit for a intermittent open or short to ground. Also check for proper installation of PROM. If knock sensor circuit is routed too close to secondary ignition wires it may induce a voltage and cause a false knock signal.

Fig. 34: Buick LeSabre Custom 1994 - Component Locations - Code P0325 Schematic (3.8L) Knock Sensor Error

Fig. 35: Buick LeSabre Custom 1994 - Component Locations - Code P0325 Flow Chart (3.8L) Knock Sensor Error

Buick LeSabre Custom 1994 - CODE P0341, CAM/CRANK ERROR

During cranking, the Ignition Control Module (ICM) monitors the crankshaft position sensor signal. Signal is used to determine correct cylinder pair to spark first. ICM processes the signal then sends a fuel control reference pulse to PCM. When PCM receives this pulse, all 6 injectors will be commanded to open for one priming shot of fuel in all cylinders. After the priming, injectors remain off for the next 6 fuel control reference pulses from ICM (2 crankshaft revolutions). This allows each cylinder a chance to use the fuel from the priming shot.

During this waiting period, a cam pulse will have been received by PCM. PCM will now begin to operate the injectors sequentially based on true camshaft position. With engine running, PCM monitors cam and fuel control references pulses received and expects to detect 6 fuel control pulses for each cam pulse.

Code P0341 will set when the following conditions are present.

• Ratio of fuel control pulses to cam pulses does not equal 6.
• Above condition for 10 occurrences during key cycle.

Code P0341 will illuminate Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. Determines if conditions necessary to set Code P0341 exist.
2. If 5 volts are not present at PCM harness connector terminal cam signal circuit, camshaft position senor may be interfacing with magnet in camshaft sprocket. Bumping the starter should correct this condition.
3. If a failure is induced in fuel control reference circuit, the 5 volts on circuit should change when faulty wiring or connection is manipulated.

Buick LeSabre Custom 1994 - Diagnostic Aids

Code P0341 indicates an intermittent fault and may not set immediately or under all conditions. Customer comments of symptom experienced may assist in isolating cause of condition. A poor connection of fault in camshaft position sensor circuits, or a faulty camshaft position sensor, may cause PCM to reinitialize injector sequence when fault occurs, causing a possible stumble or miss.

A poor connection or fault in fuel control circuit, crankshaft position sensor circuits, 18X portion of crankshaft position sensor, or damaged vanes on harmonic balancer interrupter rings will cause PCM to stop pulsing injectors when fault occurs, causing an intermittent stumble or stall.

Fig. 36: Buick LeSabre Custom 1994 - Component Locations - Code P0341 Schematic (3.8L) CAM/Crank Error

Fig. 37: Buick LeSabre Custom 1994 - Component Locations - Code P0341 Flow Chart (3.8L) CAM/Crank Error

Buick LeSabre Custom 1994 - CODE P0342, CAM SIGNAL CIRCUIT

During cranking, the Ignition Control Module (ICM) monitors the crankshaft position sensor signal. Signal is used to determine correct cylinder pair to spark first. ICM processes the signal then sends a fuel control reference pulse to PCM. When PCM receives this pulse, all 6 injectors will be commanded to open for one priming shot of fuel in all cylinders. After the priming, injectors remain off for the next 6 fuel control reference pulses from ICM (2 crankshaft revolutions). This allows each cylinder a chance to use the fuel from the priming shot.

During this waiting period, a cam pulse will have been received by PCM. PCM will now begin to operate the injectors sequentially based on true camshaft position. However, if cam signal is not present at start-up, Code P0342 will set and PCM will start sequential fuel delivery in random pattern with a one in 6 chance that fuel delivery is correct. Code P0342 will set when the following conditions are present.

• Engine is running.
• Cam signal is not received by PCM for last 5 seconds.

Code P0342 will illuminate Malfunction Indicator Light (MIL) and PCM will begin injector sequence based on last cam pulse. If cam pulses are not present at start-up, PCM will begin injector sequence based on fuel control pulses received.

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. This step verifies integrity of sensor circuits.
2. This step verifies integrity of circuit between ICM and PCM.
3. Voltage reading will be zero if camshaft gear magnet is interfacing with camshaft position sensor.
4. If voltage reading of cam signal circuit is constantly varying and connection to PCM is good, PCM is Faulty.

Buick LeSabre Custom 1994 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation, or a broken wire inside insulation. Check for:

• Poor Connection Or Damaged Harness: Inspect PCM harness connectors for backed out cam signal circuit terminal, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.
• Intermittent Test: If connections and harness are okay, monitor a DVOM connected between PCM cam signal circuit terminal and ground while moving related connectors and wiring harness. If failure is induced, voltage reading will change. This may assist in isolating the location of the malfunction.

Fig. 38: Buick LeSabre Custom 1994 - Component Locations - Code P0342 Schematic (3.8L) CAM Signal Circuit

Fig. 39: Buick LeSabre Custom 1994 - Component Locations - Code P0342 Flow Chart (3.8L) CAM Signal Circuit

Fig. 40: Buick LeSabre Custom 1994 - Component Locations - Code P0342 Flow Chart

Buick LeSabre Custom 1994 - CODE P0401, (EGR) FLOW TEST FAILURE

PCM tests exhaust gas recirculation valve by momentarily commanding valve on while monitoring engine RPM. PCM will illuminate Malfunction Indicator Light (MIL) and store Code P0401 if expected drop is not seen for a calibrated number of tests.

PCM will run EGR test when the following conditions are present.

• Codes P0122, P0123 or P0501 are not set.
• Brake has been applied.
• Engine coolant temperature is greater than 185?F (85?C).
• Throttle angle is less than one percent.
• Vehicle speed is greater than 25 MPH.
• Engine speed is 900-1100 RPM.

Code P0401 will set when the following conditions are present.

• EGR flow test will be failed and Code P0401 set if PCM does not detect a decrease in engine speed of at least 50 RPM for 6 out of 8 tests. Once 3 tests are run during an ignition cycle, PCM will not run any further flow tests until next ignition cycle. Thus, 3 or more ignition cycles will be necessary to set Code P0401. Code P0401 will illuminate Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. Ensures EGR valve is allowing EGR flow and PCM is capable of controlling EGR valve.
2. Ensures control circuit is not shorted to ground.
3. Ensures control circuit is not open and that PCM quad-driver for circuit is properly functioning.

Buick LeSabre Custom 1994 - Diagnostic Aids

An intermittent may be caused by a broken wire inside insulation. Check for:

• Poor Connection Or Damaged Harness: Inspect PCM harness connectors for backed out EGR control circuit terminal, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.
• Intermittent Test: If connections and harness are okay, monitor a DVOM connected between PCM EGR control circuit terminal and ground while moving related connectors and wiring harness. If failure is induced, voltage reading will change.

NOTE:

Check exhaust system for blockage (possibly a plugged converter) if EGR valve shows signs of excessive heat. Repair cause of restricted exhaust system as necessary. Injector stuck open may be due to stuck injector pintle, grounded driver circuit or possible faulty PCM. If conditions are not present, oil should be checked for possible fuel contamination.

Fig. 41: Buick LeSabre Custom 1994 - Component Locations - Code P0401 Schematic (3.8L) (EGR) Flow Test Failure

Fig. 42: Buick LeSabre Custom 1994 - Component Locations - Code P0401 Flow Chart (3.8L) (EGR) Flow Test Failure

Buick LeSabre Custom 1994 - CODES P0501/P0502, VSS CIRCUIT

The Vehicle Speed Sensor (VSS) in transaxle provides vehicle speed information to PCM. Voltage level and number of pulses increase with vehicle speed. PCM converts the pulsing voltage to MPH, and the MPH can be displayed using a Tech 1.

The function of the VSS buffer, used in past models, has been incorporated into PCM. PCM supplies necessary signal for instrument cluster (4004 pulses per mile) for operating speedometer and odometer.

Code P0501 will set when the following conditions are present.

• Engine is running.
• Code P0703 is not set.
• Transmission is out of Park or Neutral for more than 4 seconds.
• Vehicle speed is greater than 18 MPH.
• Brake is not applied.
• All conditions are met for 2 seconds.

Code P0502 will set when the following conditions are present.

• Vehicle speed goes from less than 3 to zero MPH in less than 2 seconds, brake not applied.
• Engine is running.
• Engine speed is greater than 3000 RPM.
• Transmission is out of Park or Neutral for more than 4 seconds.

With Codes P0501 or P0502 set, cruise control operation will not be allowed. Code will remain set for remainder of that ignition cycle, and PCM will command only 2nd and 3rd gear based on RPM and TP sensor. TCC will not be allowed to engage. Instrument cluster speedometer may be inoperative. Codes P0501 and P0502 will illuminate Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. VSS signal generator only produces a signal if drive wheels are turning greater than 3 MPH.
2. Check PROM for correct application before replacing PCM.

Buick LeSabre Custom 1994 - Diagnostic Aids

When vehicle is moving greater than 3 MPH, Tech 1 should indicate a vehicle speed. Code P0502 indicates an intermittent and may not set immediately or under all conditions. Check sensor circuits for proper connections. Ensure they are clean and tight and harness is correctly routed.

Fig. 43: Buick LeSabre Custom 1994 - Component Locations - Code P0501/P0502 Schematic (3.8L) VSS Circuit

Fig. 44: Buick LeSabre Custom 1994 - Component Locations - Code P0501/P0502 Flow Chart (3.8L) VSS Circuit

Buick LeSabre Custom 1994 - CODE P0703, TCC BRAKE SWITCH INPUT

PCM monitors status of TCC brake switch input. Code P0703 will set when the following conditions are present.

• Code P0501 is not present.
• Vehicle speed has been greater than 35 MPH for 10 seconds and back to zero MPH 5 times.
• TCC brake switch input status has not changed from released to applied, or applied to released as displayed on Tech 1.

When Code P0703 is set, PCM will not allow 4th gear, cruise control or TCC operation. Code P0703 does not illuminate the Malfunction Indicator Light (MIL).

Buick LeSabre Custom 1994 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for:

• Poor Connection Or Damaged Harness: Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
• Intermittent Test: Monitor Tech 1 while moving related connectors and wiring harness. If failure is induced, scan data will change from released to applied, or applied to released. This may assist in isolating the location of the malfunction.

Fig. 45: Buick LeSabre Custom 1994 - Component Locations - Code P0703 Schematic (3.8L) TCC Brake Switch Input

Fig. 46: Buick LeSabre Custom 1994 - Component Locations - Code P0703 Flow Chart (3.8L) TCC Brake Switch Input

Buick LeSabre Custom 1994 - CODE P0705, TRANSAXLE RANGE SWITCH

Transmission range switch is part of Transmission Mounted Neutral Start Switch (TMNSS) mounted on transaxle assembly. Transmission range switch is a multi-signal switch that sends information, relative to gear selector position, to PCM. PRNDL input consists of 4 discrete circuits to pull 4 PCM voltages low in various combinations to indicate each gear range. Voltage level of each of the circuits is represented as low equals grounded circuit and high equals open circuit. The 4 states displayed represent decoder parity, "A", "B"and "C" respectively.

Code P0705 will set when the following conditions are present.

• Ignition is on and engine off.
• Vehicle speed is zero MPH.
• PRNDL inputs indicate a gear other than Park and Neutral.
• All conditions are met for a predetermined time for 3 consecutive start-ups. Or -
• PRNDL inputs status indicators ("P", "A", "B"and "C") indicate an incorrect combination of low and high. PCM will also command stepper motor cruise control to be inhibited.

Code P0705 will cause PCM to command a drive-4 shift position. Code P0705 does not illuminate the Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. This step checks for proper operation of transmission range switch.
2. This test checks for an open or grounded circuit. When Code P0705 is present, PCM assumes drive-4 position until a correct combination is received by PCM. Some gear select positions may not be possible until fault is repaired.

Buick LeSabre Custom 1994 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for:

• Poor Connection Or Damaged Harness: Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
• Intermittent Test: Monitor Tech 1 while moving related connectors and wiring harness. If failure is induced, scan data will change from low to high, or high to low. This may assist in isolating the location of the malfunction.

Fig. 47: Buick LeSabre Custom 1994 - Component Locations - Code P0705 Schematic (3.8L) Transaxle Range Switch

Fig. 48: Buick LeSabre Custom 1994 - Component Locations - Code P0705 Flow Chart (3.8L) Transaxle Range Switch

Buick LeSabre Custom 1994 - CODE P0712, TRANSAXLE TEMP SENSOR LOW TEMP INDICATED

Transaxle temperature sensor uses a thermistor to vary signal voltage to PCM according to temperature. PCM applies and monitors a voltage to sensor. When transaxle fluid is cold sensor resistance is high. Thus, PCM will monitor a high signal voltage. As transaxle fluid warms, sensor resistance becomes less and voltage drops. At normal operating temperature of 68?F-194?F (20?C-90?C) transaxle temperature signal will measure approximately 2-4 volts.

Code P0712 will set when the following conditions are present.

• Engine run time is over 2 minutes.
• Transaxle temperature sensor signal indicates a temperature less than -40?F (-40?C).
• Above conditions for over 1.6 second.

With Code P0712 set, PCM will substitute coolant sensor temperature value for transaxle temperature. Tech 1 will continue to display actual transaxle sensor value. Code P0712 does not illuminate the Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. Determines if conditions necessary to set Code P0712 exist.
2. Simulates conditions to set Code P0713. If PCM recognizes low signal voltage and sets Code P0713, wiring and PCM are okay.

Buick LeSabre Custom 1994 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for:

• Poor Connection Or Damaged Harness: Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
• Intermittent Test: Monitor Tech 1 while moving related connectors and wiring harness. If failure is induced, scan data will change from low to high, or high to low. This may assist in isolating malfunction.
• Shifted Sensor: See TEMPERATURE-TO-RESISTANCE VALUES table to test sensor at various temperature levels to evaluate the possibility of a shifted sensor which may result in driveability complaints.
• A faulty connection, or an open in sensor circuits will cause Code P0117 to set.

Buick LeSabre Custom 1994 TEMPERATURE-TO-RESISTANCE VALUES ⁽¹⁾

Temperature ?F (?C)	Ohms
212 (100)	177
194 (90)	241
158 (70)	467
104 (40)	1459
68 (20)	3520
23 (-5)	12,300
14 (-10)	16,180
0 (-18)	25,000
-4 (-20)	28,680
-22 (-30)	52,700
-40 (-40)	100,700
(1) Measure resistance across sensor terminals.

Fig. 49: Buick LeSabre Custom 1994 - Component Locations - Code P0712 Schematic (3.8L) Transaxle Temp Sensor Low Temperature Indicated

Fig. 50: Buick LeSabre Custom 1994 - Component Locations - Code P0712 Flow Chart (3.8L) Transaxle Temp Sensor Low Temperature Indicated

Buick LeSabre Custom 1994 - CODE P0713, TRANSAXLE TEMP SENSOR HIGH TEMP INDICATED

Transaxle temperature sensor uses a thermistor to vary signal voltage to PCM according to temperature. PCM applies and monitors a voltage to sensor. When transaxle fluid is cold sensor resistance is high. Thus, PCM will monitor a high signal voltage. As transaxle fluid warms, sensor resistance becomes less and voltage drops. At normal operating temperature of 68?F-194?F (20?C-90?C) transaxle temperature signal will measure approximately 2-4 volts.

Code P0713 will set when the following conditions are present.

• Engine run time is over 1 minute.
• Transaxle temperature sensor signal indicates a temperature greater than 284?F (140?C).
• Above conditions for over 1.6 second.

With Code P0713 set, PCM will substitute ECT sensor value for transaxle temperature. Tech 1 will continue to display actual transaxle sensor value. Code P0713 does not illuminate the Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. Determines if conditions necessary to set Code P0713 exist.
2. This test determines if input circuit is shorted to ground which will cause conditions necessary for Code P0713.

Buick LeSabre Custom 1994 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for:

• Poor Connection Or Damaged Harness: Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
• Intermittent Test: Monitor Tech 1 while moving related connectors and wiring harness. If failure is induced, scan data will change from low to high, or high to low. This may assist in isolating malfunction.
• Shifted Sensor: See TEMPERATURE-TO-RESISTANCE VALUES table to test sensor at various temperature levels to evaluate the possibility of a shifted (mis-scaled) sensor which may result in driveability complaints.

Buick LeSabre Custom 1994 TEMPERATURE-TO-RESISTANCE VALUES ⁽¹⁾

Temperature ?F (?C)	Ohms
212 (100)	177
194 (90)	241
158 (70)	467
104 (40)	1459
68 (20)	3520
23 (-5)	12,300
14 (-10)	16,180
0 (-18)	25,000
-4 (-20)	28,680
-22 (-30)	52,700
-40 (-40)	100,700
(1) Measure resistance across sensor terminals.

Fig. 51: Buick LeSabre Custom 1994 - Component Locations - Code P0713 Schematic (3.8L) Transaxle Temperature Sensor High Temperature Indicated

Fig. 52: Buick LeSabre Custom 1994 - Component Locations - Code P0713 Flow Chart (3.8L) Transaxle Temperature Sensor High Temperature Indicated

Fig. 53: Buick LeSabre Custom 1994 - Component Locations - Code P0713 Flow Chart

Buick LeSabre Custom 1994 - CODE P0740, TORQUE CONVERTER CLUTCH

The Torque Converter Clutch (TCC) eliminates the loss of power to torque converter when cruise control is engaged. This allows the convenience of the automatic and the fuel economy of a manual transaxle. The main components of the system are 2 PCM controlled solenoids located inside the transaxle.

TCC is applied when the TCC apply solenoid coil is activated (on) resulting in a straight through mechanical coupling from engine to wheels. TCC is released when TCC apply solenoid coil is deactivated (off) allowing torque converter to operate in conventional manner (fluid coupling between engine and transaxle).

TCC PWM solenoid is used to vary hydraulic pressure to converter clutch regulator valve, allowing a smoother engagement of converter clutch.

Code P0740 will set when the following conditions are present.

• TP sensor throttle angle greater than 10 percent.
• Vehicle is in 3rd or 4th gear.
• VSS signal greater than 35 MPH for a 10 second minimum.
• TCC is commanded on by PCM.
• Engine RPM/vehicle speed ratio indicates TCC is not locked.
• Above conditions for over 10 seconds.

With Code P0740 set, PCM will not allow 4th gear and TCC operation, only 1st, 2nd, and 3rd gear operation. Code P0740 does not illuminate the Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. Determines whether fault is caused by a bad solenoid or control circuit.
2. Checks availability of battery voltage.
3. Checks PCM's ability to pulse PWM solenoid on and Off.

Buick LeSabre Custom 1994 - Diagnostic AIDS

Tech 1 only indicates when PCM has commanded TCC driver on, this does not confirm that TCC is actually engaged. Road test vehicle to determine if TCC is properly functioning. Engine RPM should decrease when Tech 1 indicates TCC has been turned on. If diagnosis indicates all electrical circuits and components are okay, check for hydraulic and mechanical problems.

Fig. 54: Buick LeSabre Custom 1994 - Component Locations - Code P0740 Schematic (3.8L) Torque Converter Clutch

Fig. 55: Buick LeSabre Custom 1994 - Component Locations - Code P0740 Flow Chart (3.8L) Torque Converter Clutch

Fig. 56: Buick LeSabre Custom 1994 - Component Locations - Code P0740 Flow Chart

Buick LeSabre Custom 1994 - CODE P0755, TRANSMISSION SHIFT SOLENOID "B"

The 4T60E is an electronically shifted transaxle. Within the transaxle are 4 solenoids for shift and TCC control. Solenoid "A" is energized for 1st and 4th gear operation. Solenoid "B" is energized for 1st gear as well as 2nd gear operations. The other 2 solenoids are for TCC operation. This diagnostic chart deals with shift control solenoids only.

When ignition is on, both solenoids "A" and "B" receive 12 volts. PCM will ground "A" and "B" circuits for 1st gear until a shift to 2nd gear is commanded. When vehicle speed and TP sensor reach calibrated values, PCM will turn off ground for solenoid "A" and 2nd gear is engaged. Further increase in vehicle speed will cause PCM to turn off ground for solenoid "B", engaging 3rd gear. In 3rd gear, both solenoids are de-energized. In 4th gear, only solenoid "A" is energized.

All PRNDL indications are ignored as far as transaxle shifting is concerned except for manual low gear. If PRNDL inputs indicate manual low has been selected, PCM will keep both solenoids "A" and "B" energized until approximately 5400 RPM, when PCM will force a shift by de-energizing solenoid "A". Manual 2nd and manual 3rd are controlled hydraulically within transaxle.

Code P0755 will set when the following conditions are present.

• Shift "B" is failed in off position, causing transaxle to be in 4th gear and: - Desired gear is 1st. - Throttle angle is greater than 3 percent. - VSS is greater than 5 MPH. - Codes P0122, P0123, P0501 or P0502 are not set. - Engine speed divided by vehicle speed does not indicate 1st gear. - Above conditions for 3.5 seconds.

Or

• Shift "B" is failed in on position, causing transaxle to be in 1st gear and: - Desired gear is 4th. - PRNDL is in 3rd 0r 4th. - Throttle angle is greater than 10 percent. - Codes P0122, P0123 or P0705 are not set. - Engine speed divided by vehicle speed does not indicate 4th gear (LV8 less than 80). - Above conditions for 2 seconds.

When Code P0755 is set, transaxle will be forced into 3rd gear and will not allow TCC. If Code P0755 is set due to a grounded "B" solenoid circuit, only 1st, 2nd and 3rd gear operation will be available. If circuit is open, only 3rd and 4th gear operation will be available. When the fault goes away, normal operation will be available for the balance of the key cycle. Code P0755 does not illuminate the Malfunction Indicator Light (MIL).

Fig. 57: Buick LeSabre Custom 1994 - Component Locations - Code P0755 Schematic (3.8L) Transmission Shift Solenoid "B"

Fig. 58: Buick LeSabre Custom 1994 - Component Locations - Code P0755 Flow Chart (3.8L) Transmission Shift Solenoid "B"

Buick LeSabre Custom 1994 - CODES P1350/P1361, IC CIRCUIT

When engine is cranking, Ignition Control Module (ICM) sends a spark reference and a fuel control signal to PCM. At start of crank, ICM controls ignition timing (module mode). PCM sends a 5 volts signal on by-pass circuit to switch timing to PCM control when the second fuel control pulse is recognized by PCM. Code P1350 will set at start-up is an open is present in ignition control circuit. Code P1361 will set if an open in Ignition Control (IC) circuit, or an open or grounded by-pass circuit is present during time when engine is started. Engine may be started but will run on module mode timing.

Code P1350 will set when the following conditions are present.

• IC circuit opens during engine run mode.

Code P1361 will set when the following conditions are present.

• IC circuit grounded during start-up.

Or

• PCM not commanding IC mode (open or grounded by-pass circuit) when engine is started.

When Codes P1350/P1361 are set, PCM will remove 5 volts bypass signal causing engine to run on module mode timing. PCM will illuminate Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. Checks if PCM recognizes a problem. If Codes P1350/P1361 are not set, problem is intermittent and could be caused by a loose connection.
2. With PCM disconnected, ohmmeter reading should be less than 200 ohms, which is the normal resistance of IC circuit through ICM. A higher resistance indicates a fault in IC circuit, a poor ignition module connection, or a faulty ICM.
3. If test light lights when connected between 12 volts and PCM by-pass circuit terminal, then either by-pass circuit is shorted to ground, or ICM is faulty.
4. Checks if ICM switches when by-pass circuit is energized by 12 volts through test light. If ICM switches, ohmmeter reading should shift to greater than 6000 ohms.
5. Disconnecting ICM should make ohmmeter read as if an open circuit was being monitored (infinite reading). Otherwise, IC circuit is shorted to ground.

Buick LeSabre Custom 1994 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for:

• Poor Connection Or Damaged Harness: Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
• Intermittent Test: Monitor a DVOM connected between affected terminal and ground while moving related connectors and wiring harness. If failure is induced, voltage reading will change.

Fig. 59: Buick LeSabre Custom 1994 - Component Locations - Code P1350C/P1361 Schematic (3.8L) IC Circuit

Fig. 60: Buick LeSabre Custom 1994 - Component Locations - Code P1350C/P1361 Flow Chart (3.8L) IC Circuit

Buick LeSabre Custom 1994 - CODE P1406, EGR VALVE PINTLE POSITION (1 OF 2)

PCM constantly monitors the linear EGR valve pintle position sensor to ensure the valve is responding properly to commands from PCM. Code P1406 will set when the following conditions are present.

• EGR pintle position signal indicates a voltage out of normal range of pintle position sensor, or a signal that is 10 percent greater or less than PCM commanded position.
• Either condition for up to 20 seconds.

PCM will illuminate Malfunction Indicator Light (MIL) if Code P1406 sets during 2 consecutive key cycles.

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. Checks for an EGR valve sticking partially open or an incorrect pintle position sensor feedback signal.
2. Ensures PCM is capable of controlling EGR pintle position and is reading pintle position feedback signal Properly.

Buick LeSabre Custom 1994 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for:

• Poor Connection Or Damaged Harness: Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
• Intermittent Test: If connections and harness are okay, monitor a DVOM connected between affected terminal and ground while moving related connectors and wiring harness. If failure is induced, voltage reading will change.

1. Checks will diagnose an incorrect EGR pintle position sensor input signal. This test verifies a 5 volts reference at EGR valve.
2. Ensures position signal circuit is not shorted to ground.
3. Checks position signal circuit for an open.

Fig. 61: Buick LeSabre Custom 1994 - Component Locations - Code P1406 Schematic (3.8L) EGR Valve Pintle Position

Fig. 62: Buick LeSabre Custom 1994 - Component Locations - Code P1406 Flow Chart (3.8L - 1 Of 2) EGR Valve Pintle Position

Buick LeSabre Custom 1994 - CODE P1406, EGR VALVE PINTLE POSITION (2 OF 2)

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. Checks will diagnose an incorrect EGR pintle position sensor input signal. This test verifies a 5 volts reference at EGR valve.
2. Ensures position signal circuit is not shorted to ground.
3. Checks position signal circuit for an open.

Fig. 63: Buick LeSabre Custom 1994 - Component Locations - Code P1406 Flow Chart (3.8L - 2 Of 2) EGR Valve Pintle Position

Fig. 64: Buick LeSabre Custom 1994 - Component Locations - Code P1406 Flow Chart

Buick LeSabre Custom 1994 - CODE P1530, A/C HEAD PRESSURE SWITCH

A/C head pressure switch opens at 200-220 psi. When head pressure switch interrupts ground at PCM, left fan should run at high speed.

Code P1530 will set when the following conditions are present.

• Fan request circuit is grounded during first 6 seconds of engine run time.
• Engine coolant temperature is less than 88?F (31?C).
• Ambient air temperature is less than 82?F (28?C).
• RPM is less than 1800.
• Codes P0101, P0112, P0113, P0117 or P0118 are not set.
• All above conditions must be met at the same time.

If Code P1530 is set, cooling fan(s) will run at high speed anytime A/C is requested. Code P1530 does not illuminate the Malfunction Indicator Light (MIL).

Buick LeSabre Custom 1994 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for:

• Poor Connection Or Damaged Harness: Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

Fig. 65: Buick LeSabre Custom 1994 - Component Locations - Code P1530 Schematic (3.8L) A/C Head Pressure Switch

Fig. 66: Buick LeSabre Custom 1994 - Component Locations - Code P1530 Flow Chart (3.8L) A/C Head Pressure Switch

Buick LeSabre Custom 1994 - CODE P1558, CRUISE SYSTEM PROBLEM SPS INDICATED LOW

PCM controlled cruise control system is designed to be self monitored to ensure desired cruise servo position and actual cruise servo position are equal to one another. PCM will set Code P1558 when actual servo position is too low when maximum servo is commanded.

Code P1558 will set when the following conditions are present.

• Throttle angle less than 50 percent.
• Desired servo position is 90 percent.
• Actual servo position is less than 2 percent.
• Above conditions for 3 seconds.

If Code P1558 is set, PCM will disengage cruise control and C/C set speed exceeds vehicle speed by greater than 5 MPH. P1558 does not illuminate the Malfunction Indicator Light (MIL).

Buick LeSabre Custom 1994 - Diagnostic Aids

Code P1558 may set if cruise control throttle cable binds or intermittently sticks. Outside interference such as a CB antenna lead near PCM wiring harness may induce a false SPS signal and set Code P1558.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for:

• Poor Connection Or Damaged Harness: Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

Fig. 67: Buick LeSabre Custom 1994 - Component Locations - Code P1558 Schematic (3.8L) Cruise System Problem SPS Indicated Low

Fig. 68: Buick LeSabre Custom 1994 - Component Locations - Code P1558 Flow Chart (3.8L) Cruise System Problem SPS Indicated Low

Buick LeSabre Custom 1994 - CODE P1561, CRUISE VENT SOLENOID

Cruise switch within turn signal lever receives ignition voltage from a 15-amp fuse to turn signal lever cruise switches. Cruise ON/OFF, SET/COAST and RESUME/ACCEL switches are inputs to cruise portion of PCM.

Cruise servo vent and vacuum solenoids output are controlled by high side drivers in PCM. When ignition is on, PCM looks at these output lines and will set codes if an incorrect status is seen on any line.

Vent solenoid is a normally open (de-energized) solenoid valve that allows vacuum in cruise servo to be depleted. When solenoid is on (energized), cruise servo holds vacuum allowing servo to remain retracted and hold throttle open.

Code P1561 will set when the following conditions are present.

• Vent driver circuit is shorted to voltage when vent solenoid is commanded off.
• Vent driver circuit is open.
• Vent driver circuits shorted to ground when vent solenoid is commanded on.
• One of above conditions are met for more than half of a second.

When Code P1561 is set, PCM will not allow cruise control operation. P1561 does not illuminate the Malfunction Indicator Light (MIL).

Buick LeSabre Custom 1994 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for:

• Poor Connection Or Damaged Harness: Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

Fig. 69: Buick LeSabre Custom 1994 - Component Locations - Code P1561 Schematic (3.8L) Cruise Vent Solenoid

Fig. 70: Buick LeSabre Custom 1994 - Component Locations - Code P1561 Flow Chart (3.8L) Cruise Vent Solenoid

Fig. 71: Buick LeSabre Custom 1994 - Component Locations - Code P1561 Flow Chart

Buick LeSabre Custom 1994 - CODE P1562, CRUISE VACUUM SOLENOID

Cruise switch within turn signal lever receives ignition voltage from a 15-amp fuse to turn signal lever cruise switches. Cruise ON/OFF, SET/COAST and RESUME/ACCEL switches are inputs to cruise portion of PCM.

Cruise servo vent and vacuum solenoids output are controlled by high side drivers in PCM. When ignition is on, PCM looks at these output lines and will set codes if an incorrect status is seen on any line.

Vacuum solenoid is a normally closed solenoid valve that blocks the flow of vacuum to cruise servo. When solenoid is on (energized), solenoid valve opens allowing vacuum to be drawn into servo.

Code P1562 will set when the following conditions are present.

• Solenoid driver circuit is shorted to voltage when vacuum solenoid is commanded off.
• Solenoid driver circuit is open.
• Solenoid driver circuit is shorted to ground when vacuum solenoid is commanded on.
• One of above conditions are met for more than half of a second.

When Code P1562 is set, PCM will not allow cruise control operation. P1562 does not illuminate the Malfunction Indicator Light (MIL).

Buick LeSabre Custom 1994 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for:

• Poor Connection Or Damaged Harness: Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

Fig. 72: Buick LeSabre Custom 1994 - Component Locations - Code P1562 Schematic (3.8L) Cruise Vacuum Solenoid

Fig. 73: Buick LeSabre Custom 1994 - Component Locations - Code P1562 Flow Chart (3.8L) Cruise Vacuum Solenoid

Fig. 74: Buick LeSabre Custom 1994 - Component Locations - Code P1562 Flow Chart

Buick LeSabre Custom 1994 - CODE P1565, CRUISE SERVO POSITION

PCM applies and monitors 5 volts to cruise control servo position sensor through PCM servo position sensor terminal and receives a returned frequency from servo terminal "B" on the same circuit. Depending on actual servo position, AC frequency will vary indicating to PCM position of servo blade. PCM uses this information to control servo position when cruise is engaged. Code P1565 will set when the following conditions are present.

• Servo position signal circuit is open, grounded or shorted to voltage.

Or

• Ground circuit (low) is open.

When Code P1565 is set, PCM will not allow cruise control operation. P1565 does not illuminate the Malfunction Indicator Light (Mil).

Buick LeSabre Custom 1994 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for:

• Poor Connection Or Damaged Harness: Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

Fig. 75: Buick LeSabre Custom 1994 - Component Locations - Code P1565 Schematic (3.8L) Cruise Servo Position

Fig. 76: Buick LeSabre Custom 1994 - Component Locations - Code P1565 Flow Chart (3.8L) Cruise Servo Position

Buick LeSabre Custom 1994 - CODE P1567, CRUISE SWITCHES CIRCUIT

Power is supplied to cruise control switches and cruise brake switch as well as other circuits by the ignition switch. Circuit is protected by a 15-amp fuse. Code P1567 will set when the following conditions are present.

• ON/OFF switch is open between cruise engage switch and PCM.
• SET/COAST switch is indicated closed for more than 7 1/2 minutes (switch problem).
• RESUME/ACCEL switch is indicated closed for more than 7 1/2 minutes (switch problem).
• Cruise brake signal is open to PCM (no change in status of cruise brake switch) when vehicle makes 5 stops from 35 MPH (for more than 10 seconds) down to zero MPH.
• Any of above circuits are shorted to voltage.
• One of above conditions are met.

When Code P1567 is set, PCM will not allow cruise control operation. P1567 does not illuminate the Malfunction Indicator Light (MIL).

NOTE:

A short to ground in cruise ON/OFF circuit, SET/COAST, cruise/brake or RESUME/ACCELL will cause a failure of cruise engagement switch. It will not blow the 15-amp fuse.

Buick LeSabre Custom 1994 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for:

Fig. 77: Buick LeSabre Custom 1994 - Component Locations - Code P1567 Schematic (3.8L) Cruise Switches Circuit

Fig. 78: Buick LeSabre Custom 1994 - Component Locations - Code P1567 Flow Chart (3.8L) Cruise Switches Circuit

Buick LeSabre Custom 1994 - CODE P1568, CRUISE SYSTEM PROBLEM (SPS INDICATED HIGH)

PCM controlled cruise control system is designed to be self monitored to ensure desired cruise servo position and actual cruise servo position are equal to one another. When Code P1568 is set, vehicle may operate in power management mode and Code P1599 will set. While in power management, PCM will shut off fuel to 3 cylinders to avoid over-revving engine in case throttle is being held open by a sticking cruise control throttle cable, brake vacuum release valve, or cruise control servo. Power management may be perceived as a severe engine miss or lack of power. Code P1568 will set when the following conditions are present.

• Actual servo position is greater than 15 percent above desired servo position of zero percent.
• Above condition met for one second.

When Code P1568 is set, PCM will not allow cruise control operation. Condition that causes Code P1568 may cause vehicle to operate in power management and Code P1599 to set. P1568 does not illuminate the Malfunction Indicator Light (MIL).

Buick LeSabre Custom 1994 - Diagnostic Aids

Code P1568 may set if cruise control throttle cable binds or intermittently sticks. Code P1568 can also be set by manually compressing cruise servo to raise engine speed. Outside interference such as a CB antenna lead near PCM wiring harness may induce a false SPS signal and set Code P1568.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for:

• Poor Connection Or Damaged Harness: Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

Fig. 79: Buick LeSabre Custom 1994 - Component Locations - Code P1568A Schematic (3.8L) Cruise System Problem (SPS Indicated High)

Fig. 80: Buick LeSabre Custom 1994 - Component Locations - Code P1568A Flow Chart (3.8L) Cruise System Problem (SPS Indicated High)

Buick LeSabre Custom 1994 - CODE P1571, TRACTION CONTROL DESIRED TORQUE OUT OF RANGE

Traction control system uses anti-lock brake system in conjunction with PCM fuel and ignition controls to limit drive wheel slippage during acceleration. PCM controlled portion of traction control system reduces engine torque by any or all of following methods.

• Retarding spark advance.
• Altering air/fuel ratio.
• Altering boost duty cycle (VIN 1 only).
• Shutting off up to 3 injectors.

To determine amount of torque reduction required, PCM monitors desired torque PWM signal circuit from Electronic Brake and Traction Control Module (EBTCM). PCM also provides a delivered torque PWM signal, informing EBTCM how much torque is being produced by engine. Code P1571 will set when the following condition is present.

• If desired torque signal PWM duty cycle is less than 5 percent or greater than 95 percent. Code P1571 will set indicating a problem with desired torque input on circuit.

When Code P1571 is set, PCM will command EBTCM via serial data circuit to set ABS/TCS DTC 75, turn off traction control, and illuminate TRACTION OFF indicator. P1571 does not illuminate the Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. Checks circuit for an open or short to ground.
2. Ensures EBTCM is proving a proper PWM signal to PCM.

Buick LeSabre Custom 1994 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for:

• Poor Connection Or Damaged Harness: Inspect PCM harness for an open or short to ground in desired torque circuit, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
• Intermittent Test: Using a DVOM observe voltage between PCM desired torque terminal and ground while moving related connectors and wiring harness with warm engine running. If failure is induced, voltage reading will change. This may assist in isolating the location of the malfunction.

Fig. 81: Buick LeSabre Custom 1994 - Component Locations - Code P1571 Schematic (3.8L) Traction Control Desired Torque Out Of Range

Fig. 82: Buick LeSabre Custom 1994 - Component Locations - Code P1571 Flow Chart (3.8L) Traction Control Desired Torque Out Of Range

Buick LeSabre Custom 1994 - CODE P1573, TRACTION CNTRL FAULT LOSS OF ABS/TCS SERIAL DATA

PCM uses the serial data line to communicate with various other components and systems within vehicle. If PCM does not receive data from Electronic Brake and Traction Control Module (EBTCM), PCM will store Code P1573 indicating loss of communication with ABS/TCS system. Code P1573 will set when the following conditions are present.

• Code P1630 is not set.
• PCM has detected communication error for .5 second.

When Code P1573 is set, PCM will not be able to communicate with EBTCM. This will cause EBTCM to set to set ABS DTC 76, disable traction control, and illuminate TRACTION OFF indicator. P1573 does not illuminate the Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. Checks if EBTCM is able to transmit data and ensures serial data circuit to EBTCM is not open.

Buick LeSabre Custom 1994 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for:

• Poor Connection Or Damaged Harness: Inspect wiring harness for an open or short to ground in serial data circuit, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
• Intermittent Test: Observe ABS data on Tech 1 while moving related connectors and wiring harness. If failure is induced, Tech 1 data will stop updating. This may assist in isolating the location of the malfunction.

Fig. 83: Buick LeSabre Custom 1994 - Component Locations - Code P1573 Schematic (3.8L) Traction Cntrl Fault Loss Of ABS/TCS Serial Data

Fig. 84: Buick LeSabre Custom 1994 - Component Locations - Code P1573 Flow Chart (3.8L) Traction Cntrl Fault Loss Of ABS/TCS Serial Data

Buick LeSabre Custom 1994 - CODE P1599, CRUISE POWER MANAGEMENT

PCM controlled cruise control system is designed to be self monitored to ensure desired cruise servo position and actual cruise servo position are equal to one another. If actual servo position is too high, PCM will set Code P1568, and vehicle will operate in power management mode. While in power management, PCM will shut off fuel to 3 cylinders to avoid over-revving engine in case throttle is being held open by a sticking cruise control throttle cable, brake vacuum release valve, or cruise control servo. Code P1599 is an information code included to alert service that vehicle has operated in power management mode. Code P1599 will set when vehicle has operated in power management mode.

Buick LeSabre Custom 1994 - Diagnostic Aids

A cruise control throttle cable which binds or intermittently sticks may cause vehicle to operate in power management and Code P1599 to set. Code P1599 can also be set by manually compressing cruise servo to raise engine speed. Outside interference such as a CB antenna lead near PCM wiring harness may induce a false SPS signal and set Code P1599.

Fig. 85: Buick LeSabre Custom 1994 - Component Locations - Code P1599 Schematic (3.8L) Cruise Power Management

Fig. 86: Buick LeSabre Custom 1994 - Component Locations - Code P1599 Flow Chart (3.8L) Cruise Power Management

Buick LeSabre Custom 1994 - CODE P1619, ENGINE OIL LIFE MONITOR RESET CIRCUIT

To determine the engine oil life remaining, PCM monitors engine coolant temperature, the number of crankshaft revolutions, vehicle speed, engine speed, and calculated oil temperature. When PCM determines that engine oil is near the end of its useful life, it will command instrument cluster via serial data circuit to illuminate the CHANGE OIL SOON indicator or CHANGE OIL SOON/NOW message after start-up. PCM will command the CHANGE OIL SOON indicator or CHANGE OIL SOON/NOW message on after each start-up until the engine oil life monitor is reset by grounding oil life monitor reset input circuit through the oil life monitor reset switch for more than 5 seconds. Code P1619 will set when the following condition is present.

• Oil life monitor reset input circuit is grounded for more than 60 seconds.

P1619 does not illuminate the Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. Checks circuit for a short to ground.
2. Checks for a faulty PCM or an intermittent condition.

Fig. 87: Buick LeSabre Custom 1994 - Component Locations - Code P1619 Schematic (3.8L) Engine Oil Life Monitor Reset Circuit

Fig. 88: Buick LeSabre Custom 1994 - Component Locations - Code P1619 Flow Chart (3.8L) Engine Oil Life Monitor Reset Circuit

Buick LeSabre Custom 1994 - CODE P1623, PROM ERROR

Check that PROM is correctly inserted in the socket. If okay, replace PROM, clear memory and recheck. If Code P1623 reappears, replace PCM.

NOTE:

To prevent possible electrostatic discharge damage to PCM or PROM, DO NOT touch component leads. DO NOT remove integrated circuit from carrier.

Buick LeSabre Custom 1994 - CODES P1626/1629, PASS-KEY II FUEL ENABLE CIRCUIT

When ignition is on, theft deterrent module reads the key resistor pellet. If proper resistance is recognized by theft deterrent module, it sends a PWM fuel enable signal to PCM. PCM looks for this signal during crank and allows fuel delivery by enabling the injectors when signal is recognized.

Code P1626 will set when the following condition is present.

• Fuel enable signal is lost after engine has started.

Code P1629 will set when the following condition is present.

• Fuel enable signal is not present during crank.

If fuel enable signal is not seen during crank, injectors will be disabled and PCM will store Code P1629, indicating a problem with theft deterrent system or fuel enable input circuit. Code P1629 will result in a cranks but will not run condition. P1629 does not illuminate the Malfunction Indicator Light (MIL).

If fuel enable signal is lost while engine is running, PCM will store Code P1626 and vehicle will run normally. As long as Code P1626 is stored, PCM will ignore any absence of fuel enable signal and vehicle will restart and run as long as problem is isolated to fuel enable circuit only. P1626 does not illuminate the Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. If vehicle does not crank with Code P1626 or P1629 stored, problem affects the entire theft deterrent system and is not isolated to fuel enable circuit.
2. PCM supplies 5 volts to fuel enable input circuit which theft deterrent module pulses to ground when correct key resistance is recognized. This test ensures PCM is supplying 5 volts and circuit is not open or shorted to ground.
3. Checks signal from theft deterrent module. DC frequency on circuit should measure approximately 50 hertz.
4. Checks for a faulty PCM or intermittent condition by clearing Code P1626 or P1629. Since PCM ignores the absence of a fuel enable signal only when Code P1626 or P1629 is stored, vehicle should not start if problem is present and Code P1626 or P1629 has been cleared.

Buick LeSabre Custom 1994 - Diagnostic Aids

An intermittent Code P1626 or P1629 and/or a possible no-start may be caused by the following.

• Loss Of Power Or Ground To Theft Deterrent Module: A loose ground or poor ignition or battery condition could cause an intermittent loss of the PASS-Key II fuel enable signal and Codes P1626 and P1629 to be set.
• Dirty, Damaged, Or Loose Connections Or Damaged Harness: Check for any damage to harness which could cause an intermittent open or short to ground, backed out terminals at PCM and theft deterrent module connectors, broken locks, improperly formed or damaged terminals.

Fig. 89: Buick LeSabre Custom 1994 - Component Locations - Code P1626A/P1629 Schematic (3.8L) Pass-Key II Fuel Enable Circuit

Fig. 90: Buick LeSabre Custom 1994 - Component Locations - Code P1626A/P1629 Flow Chart (3.8L) Pass-Key II Fuel Enable Circuit

Fig. 91: Buick LeSabre Custom 1994 - Component Locations - Code P1626A/1629 Flow Chart

Buick LeSabre Custom 1994 - CODE P1630, SYSTEM VOLTAGE HIGH/LOW

PCM monitors system voltage on PCM ignition feed terminal. Code P1630 will set when the following condition is present.

• PCM detects voltage greater than 17.3 volts or less than 9 volts for more than 10 seconds while engine is running.

With Code P1630 set, transaxle will be forced to 3rd gear and TCC will not be allowed to engage. This is to avoid erratic shifting due to improper voltages. PCM will illuminate Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. Test generator output to determine proper operation of voltage regulator. Run engine at moderate speed and measure voltage across battery. If less than 9 volts or greater than 17.3 volts, repair generator.

Buick LeSabre Custom 1994 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation, a wire broken inside insulation or poor PCM grounds. Check for:

• Poor Connection Or Damaged Harness: Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
• Intermittent Test: Using Tech 1, monitor SYSTEM VOLTS display while moving related connectors and wiring harness. If failure is induced, display will abruptly change. This may assist in isolating the location of the malfunction. An engine stall while manipulating harness indicates PCM has lost voltage at ignition feed terminal (Pink wire). Check for loose connectors in power feed circuit.

NOTE:

Charging with a battery charger while starting engine may set Code P1630.

Fig. 92: Buick LeSabre Custom 1994 - Component Locations - Code P1630 Schematic (3.8L) System Voltage High/Low

Fig. 93: Buick LeSabre Custom 1994 - Component Locations - Code P1630 Flow Chart (3.8L) System Voltage High/Low

Fig. 94: Buick LeSabre Custom 1994 - Component Locations - Code P1630 Flow Chart

Buick LeSabre Custom 1994 - CODE P1640, QDM NO. 1 CIRCUIT

PCM is used to control several components as shown in wiring schematic. PCM controls these devises through use of a Quad-Driver Module (QDM). When PCM is commanding a component on, voltage potential of output circuit will be low (near zero volt). When PCM is commanding output circuit to a component off, voltage potential of circuit will be high (near battery voltage). Primary function of QDM is to supply ground for component being controlled.

Each QDM has a fault line which is monitored by PCM. Fault line signal is available on data stream for scan tool test equipment display on Tech 1. PCM will compare voltage at QDM based on accepted values of fault line. If QDM No. 1 fault detection circuit senses a voltage other than accepted value, fault line will go from a low signal on data stream to a high signal and Code P1640 will set.

Code P1640 will set when the following conditions are present.

• Engine is running.
• PCM detects an improper voltage level on a circuit connected to QDM No. 1.
• Brake not applied.
• Above conditions met for 5 seconds.

PCM will illuminate Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. If QDM related code is stored, diagnose that code first. Repair made to related code will repair Code P1640 also.
2. If QDM No. 1 symptoms are present, checks on chart 2 of 2 should isolate cause of fault.
3. This test will determine which circuit is out of Specifications.
4. This test will determine if problem is circuit or component.
5. As the factory installed PCM is protected with an internal circuit breaker, it is highly unlikely that PCM needs to be replaced.

Buick LeSabre Custom 1994 - Diagnostic Aids

Monitor voltage at each terminal shown above while moving related harness connectors, including PCM harness. If failure is induced, voltage will change. This may assist in isolating an intermittent condition. Check for bent pins at PCM and PCM connector terminals. If code reoccurs with no apparent connector problem, replace PCM.

Fig. 95: Buick LeSabre Custom 1994 - Component Locations - Code P1640 Schematic (3.8L) QDM No. 1 Circuit

Fig. 96: Buick LeSabre Custom 1994 - Component Locations - Code P1640 Flow Chart (3.8L - 1 Of 2) QDM No. 1 Circuit

Fig. 97: Buick LeSabre Custom 1994 - Component Locations - Code P1640 Flow Chart (3.8L - 2 Of 2) QDM No. 1 Circuit

Buick LeSabre Custom 1994 - CODE P1650, QDM NO. 2

PCM is used to control several components as shown in wiring schematic. PCM controls these devises through use of a Quad-Driver Module (QDM). When PCM is commanding a component on, voltage potential of output circuit will be low (near zero volt). When PCM is commanding output circuit to a component off, voltage potential of circuit will be high (near battery voltage). Primary function of QDM is to supply ground for component being controlled.

Each QDM has a fault line which is monitored by PCM. Fault line signal is available on data stream for scan tool test equipment display on Tech 1. PCM will compare voltage at QDM based on accepted values of fault line. If QDM No. 2 fault detection circuit senses a voltage other than accepted value, fault line will go from a low signal on data stream to a high signal and Code P1650 will set. Code P1650 will set when the following conditions are present.

• Engine is running.
• PCM detects an improper voltage level on a circuit connected to QDM No. 2.
• Above conditions met for 5 seconds.

Code P1650 will not illuminate Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. If QDM related code is stored, diagnose that code first. Repair made to related code will repair Code P1650 also.
2. This test will determine which circuit is out of specifications.
3. This test will determine if problem is circuit or component.
4. As the factory installed PCM is protected with an internal circuit breaker, it is highly unlikely that PCM needs to be replaced.

Buick LeSabre Custom 1994 - Diagnostic Aids

Monitor voltage at each terminal shown above while moving related harness connectors, including PCM harness. If failure is induced, voltage will change. This may assist in isolating an intermittent condition. Check for bent pins at PCM and PCM connector terminals. If code reoccurs with no apparent connector problem, replace PCM.

Fig. 98: Buick LeSabre Custom 1994 - Component Locations - Code P1650 Schematic (3.8L) QDM No. 2

Fig. 99: Buick LeSabre Custom 1994 - Component Locations - Code P1650 Flow Chart (3.8L - 1 Of 2) QDM No. 2

Fig. 100: Buick LeSabre Custom 1994 - Component Locations - Code P1650 Flow Chart (3.8L - 2 Of 2) QDM No. 2

Fig. 101: Buick LeSabre Custom 1994 - Component Locations - Code P1650 Flow Chart

Buick LeSabre Custom 1994 - CODE P1670, QDM NO. 4

PCM is used to control several components as shown in wiring schematic. PCM controls these devises through use of a Quad-Driver Module (QDM). When PCM is commanding a component on, voltage potential of output circuit will be low (near zero volt). When PCM is commanding output circuit to a component off, voltage potential of circuit will be high (near battery voltage). Primary function of QDM is to supply ground for component being controlled.

Each QDM has a fault line which is monitored by PCM. Fault line signal is available on data stream for scan tool test equipment display on Tech 1. PCM will compare voltage at QDM based on accepted values of fault line. If QDM No. 4 fault detection circuit senses a voltage other than accepted value, fault line will go from a low signal on data stream to a high signal and Code P1670 will set. Code P1670 will set when the following conditions are present.

• Engine is running.
• PCM detects an improper voltage level on a circuit connected to QDM No. 4.
• Above conditions met for 5 seconds.

Code P1670 will not illuminate Malfunction Indicator Light (MIL).

NOTE:

Test numbers refer to numbers on diagnostic chart.

1. If QDM No. 4 related symptoms are present, checks on chart 2 of 2 should isolate cause of fault.
2. This test will determine which circuit is out of specifications.
3. This test will determine if problem is circuit or component.
4. As the factory installed PCM is protected with an internal circuit breaker, it is highly unlikely that PCM needs to be replaced.

Buick LeSabre Custom 1994 - Diagnostic Aids

Monitor voltage at each terminal shown above while moving related harness connectors, including PCM harness. If failure is induced, voltage will change. This may assist in isolating an intermittent condition. Check for bent pins at PCM and PCM connector terminals. If code reoccurs with no apparent connector problem, replace PCM.

Fig. 102: Buick LeSabre Custom 1994 - Component Locations - Code P1670 Schematic (3.8L) QDM No. 4

Fig. 103: Buick LeSabre Custom 1994 - Component Locations - Code P1670 Flow Chart (3.8L - 1 Of 2) QDM No. 4

Fig. 104: Buick LeSabre Custom 1994 - Component Locations - Code P1670 Flow Chart (3.8L - 2 Of 2) QDM No. 4

Buick LeSabre Custom 1994 - SUMMARY

If no hard fault codes are present, driveability symptoms exist or intermittent codes exist, proceed to TESTS W/O CODES article in this section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.

Buick LeSabre Custom 1994 - WIRING DIAGRAMS

Fig. 105: Buick LeSabre Custom 1994 - Component Locations - 3.8L (VIN L & VIN 1) PCM Wiring Diagram (1 Of 3)

Fig. 106: Buick LeSabre Custom 1994 - Component Locations - 3.8L (VIN L & VIN 1) PCM Wiring Diagram (2 Of 3)

Fig. 107: Buick LeSabre Custom 1994 - Component Locations - 3.8L (VIN L & VIN 1) PCM Wiring Diagram (3 Of 3)