Buick Skylark Gran Sport 1990 - 1990 ENGINE PERFORMANCE 2.3L PFI Model Self-Diagnostics

Buick Skylark Gran Sport 1990 - BODY DESIGNATION TABLE

Buick Skylark Gran Sport 1990 BODY DESIGNATION

Body Code	Make
"L"	Beretta
"N"	Cutlass Calais, Grand Am, Skylark
"W"	Cutlass Supreme, Grand Prix

Buick Skylark Gran Sport 1990 - 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 article. Failure to do so may result in lost diagnostic time.

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

Buick Skylark Gran Sport 1990 - SELF-DIAGNOSTIC SYSTEM DESCRIPTION

The ECM is equipped with a self-diagnostic system, which detects system failures or abnormalities. When a malfunction occurs, ECM will illuminate the SERVICE ENGINE SOON light located on instrument panel. When malfunction is detected and light is turned on, a corresponding trouble code will be stored in ECM memory. To retrieve stored codes, see RETRIEVING CODES (NON-SCAN) in this article. Malfunctions are recorded as HARD FAILURES or as INTERMITTENT FAILURES.

Buick Skylark Gran Sport 1990 - Hard Failures

Hard failures cause SERVICE ENGINE SOON light to illuminate and remain on until the 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 unit will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional, but loss of good driveability will most likely be encountered.

Buick Skylark Gran Sport 1990 - Intermittent Failures

Intermittent failures cause SERVICE ENGINE SOON light to flicker or illuminate and go out about 10 seconds after the intermittent fault goes away. The corresponding trouble code, however, will be retained in ECM memory. If related fault does not reoccur within 50 engine restarts, related trouble code will be erased from ECM memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See INTERMITTENTS in H - TESTING W/O CODES article in this section.

Buick Skylark Gran Sport 1990 - DIAGNOSTIC PROCEDURE

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

1. Make sure all engine systems not related to the computer system are operating properly. Do not proceed with testing unless all other problems have been repaired. Appropriate DIAGNOSTIC CIRCUIT CHECK for that system MUST be performed prior to utilizing trouble code charts. See BASIC TESTING article.
2. If trouble codes were displayed (other than Code 12), decide whether codes are hard or intermittent trouble codes. Hard codes will cause the SERVICE ENGINE SOON light to illuminate continuously while engine is running. See HARD OR INTERMITTENT TROUBLE CODE DETERMINATION in this article. For diagnosing hard codes, proceed to appropriate trouble code chart in this article. For diagnosing intermittent codes, proceed to INTERMITTENTS in H - TESTING W/O CODES article. Exceptions are Code 13, 15, 24, 44 and 45 charts, which may be used to help diagnose intermittent codes.
3. If no trouble codes were displayed and a driveability problem exists, refer to SYMPTOMS in H - TESTING W/O CODES article. The comments there will send you to the proper system or component to check in SYSTEM/COMP TESTS article.
4. After any repairs are made, clear any trouble codes and perform SYSTEM PERFORMANCE CHECK or FIELD SERVICE MODE check in BASIC TESTING article.

Buick Skylark Gran Sport 1990 - RETRIEVING CODES (NON-SCAN)

1. Turn ignition on. Do not start engine. SERVICE ENGINE SOON light should glow. Locate Assembly Line Data Link (ALDL) connector attached to ECM wiring harness. Most ALDL connectors are located under dash on driver's side of vehicle. For exact location of ALDL, see appropriate COMPONENT LOCATIONS illustration in SYSTEM/COMP TESTS article. Turn ignition on. Insert jumper wire from terminal "B" (diagnostic test terminal) to terminal "A" (ground) of ALDL connector. See Fig. 1 .

   NOTE:

   Inserting jumper wire into test and ground terminals of ALDL connector with engine running will cause fuel injected vehicles to enter field service mode. Codes will not flash if this is done. See FIELD SERVICE MODE in BASIC TESTING article.

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   Fig. 1: Buick Skylark Gran Sport 1990 - Component Locations - ALDL Connector Terminal Identification
   

2. SERVICE ENGINE SOON light should begin to flash codes. Each code will be repeated 3 times. If codes are not flashed, perform DIAGNOSTIC CIRCUIT CHECK in BASIC TESTING article. To exit diagnostic mode, turn ignition off and remove jumper wire from ALDL connector.

Buick Skylark Gran Sport 1990 - READING TROUBLE CODES

The ECM 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 the SERVICE ENGINE SOON light, or by reading the output of a diagnostic "Scan" tester connected to the ALDL connector. The tester is faster to use, more accurate, and capable of reading information which otherwise would necessitate testing individual ECM and sensor/solenoid connector terminals with a digital voltmeter. See SCAN DATA TABLES and SCAN TESTER USAGE in this article.

NOTE:

When using a "Scan" tester, there is a time delay between serial data updates. For instantaneous response, a digital voltmeter must be used.

If "Scan" tester is not available, it is possible to read flashes of the SERVICE ENGINE SOON light by grounding the diagnostic terminal of the ALDL with ignition on and engine off. For example, FLASH, FLASH, pause, FLASH, longer pause, identifies Code 21. The first series of flashes are the first digit of trouble code. The second series of flashes are the second digit of trouble code. Trouble codes are displayed starting with the lowest numbered code. Each code is displayed 3 times. Codes will continue to repeat as long as ALDL 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 may require operation for 5 minutes or longer at normal operating temperature, road speed and load. Therefore, some codes may not set in a service bay operational mode.

Buick Skylark Gran Sport 1990 ECM TROUBLE CODE DEFINITION

Code No.	Circuit Affected
12 (1)	No RPM reference pulse
13	Open oxygen sensor circuit
14	CTS signal voltage low
15	CTS signal voltage high
16	System voltage high
21	TPS signal voltage high
22	TPS signal voltage low
23	MAT sensor signal voltage high
"	M/C solenoid voltage low
24	VSS circuit
25	MAT sensor signal voltage low
26	Quad-Driver error
27, 28 & 29	Gear switch problem
31	Wastegate error (turbo)
"	Park/Neutral switch
32	EGR system error
33	MAP sensor signal voltage high
"	MAF sensor signal voltage high (PFI)
34	MAP sensor signal voltage low
"	MAF sensor signal voltage low (PFI)
35	IAC idle speed error
38	Brake switch
39	TCC
41	C(3)I ignition - cam sensor loss
"	Cylinder select error (MEM-CAL)
42	EST circuit open or grounded
43	ESC retard signal too low
44	Lean exhaust indicated
45	Rich exhaust indicated
46	Anti-theft fault
"	Power steering pressure switch
48	Misfire diagnosis
51	Faulty PROM, MEM-CAL or ECM
52	Faulty/missing CALPAC or MEM-CAL
52	Engine oil temperature low (Corvette)
53	Faulty alternator, voltage high
"	EGR system malfunction
"	Anti-theft circuit fault
54	Fuel pump voltage low
55	Faulty ECM
61	Degraded O2 sensor
62	Gear switch error
62	Engine oil temperature high (Corvette)
63	EGR flow error
64	EGR flow error
65	EGR flow error
"	Fuel injector current low
66	A/C pressure sensor voltage out of specification
(1) Display of a Code 12 is normal when no reference pulses are received by ECM (engine not running).

NOTE:

Trouble code charts should only be used if SERVICE ENGINE SOON light is illuminated (indicating a current problem exists). Exceptions are Code 13, 15, 24, 44 and 45 charts, which may be used to help diagnose intermittent codes. Anytime Codes 51, 52, 54 or 55 are displayed with another code, start with 50-series code first, then proceed to low profile numbered codes.

Buick Skylark Gran Sport 1990 - HARD OR INTERMITTENT TROUBLE CODE DETERMINATION

During any diagnostic procedure, it must be determined 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, proceed as follows:

1. MANUALLY 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, MANUALLY enter diagnostic mode. Read and record trouble codes. This will reveal hard failure codes. Codes 13, 15, 24, 44, 45 and 55 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. Exceptions are noted under each DIAGNOSTIC PROCEDURE.

Buick Skylark Gran Sport 1990 - CLEARING TROUBLE CODES

Turn ignition switch to ON position and ground diagnostic terminal lead at ALDL connector. Turn ignition switch to OFF position and remove ECM fuse from fuse block for 10 seconds. Replace fuse. Remove diagnostic terminal ground lead.

Buick Skylark Gran Sport 1990 - ECM LOCATION

On most vehicles the ECM is located behind the right side of the dash, or behind the right kick panel. On the Grand Prix and Lumina, the ECM is located on the right side of the engine compartment. On Corvette, the ECM is located in the left rear corner of the engine compartment, next to the battery.

Buick Skylark Gran Sport 1990 - DIAGNOSTIC MATERIALS Diagnostic Aids

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

Buick Skylark Gran Sport 1990 - Field Service Mode Check (Fuel Injected)

On fuel injected models, SERVICE ENGINE SOON light will indicate operational mode of engine if ALDL is grounded while engine is running. This test confirms proper operation of fuel system and verifies closed loop operation. Clear codes and perform this test after any repair is completed. Field service mode check can be found by proceeding to FIELD SERVICE MODE CHECK (FUEL INJECTED) in BASIC TESTING article.

Buick Skylark Gran Sport 1990 - Special Tools (Diagnostic)

NOTE:

Special "Scan" testers plugged into the ALDL may be used to read trouble codes and check voltages in the system on the serial data line (terminal "E" on EFI and terminal "M" on EFI with P-4 systems). These testers can save a great deal of time. For additional information, see SCAN TESTER USAGE and SCAN TESTER DATA tables in this article.

The computerized engine control system is most easily diagnosed using a "Scan" tester; however, other tools may aid in diagnosing problems if a "Scan" tester is unavailable. These tools are a tachometer, dwell meter, test light, ohmmeter, digital voltmeter with 10-megohm input impedance (minimum), vacuum pump, vacuum gauge, fuel injector test lights (TBI and PFI) and 6 jumper wires 6" long (one wire with female connectors at both ends, one wire with male connector 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.

Before engine reaches operating temperature, dwell should be fixed between 10-50 degrees, indicating open loop operation. With engine at operating temperature and idling, dwell meter needle should be varying between 10-50 degrees. This indicates closed loop operation. If (after reaching normal operating temperature) dwell is fixed between 10-50 degrees, less than 10 degrees or more than 50 degrees, refer to SYSTEM PERFORMANCE CHECK in BASIC TESTING article.

Buick Skylark Gran Sport 1990 - SCAN TESTER USAGE

NOTE:

Prior to connection of "Scan" tester to vehicle, diagnostic system should be checked to determine if system is operating properly and if information received by "Scan" tester will be accurate. This is done by performing appropriate DIAGNOSTIC CIRCUIT CHECK in BASIC TESTING article. If vehicle does not pass diagnostic circuit check, information received by "Scan" tester may be invalid.

The "Scan" tester is a specialized tester which, when plugged into ALDL, 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 back-probe sensors and connectors. "Scan" testers cut down diagnostic time dramatically by furnishing input data (voltage signals) which can be compared to specification parameters. See SCAN DATA tables in this article. They may also furnish information on output device (solenoids and motors) status. However, status parameters are only an indication that output signals have been sent to devices by the ECM. It does not indicate if devices have responded properly to that signal. This will need to be verified at output device using a voltmeter or test light.

NOTE:

Code 12 should always exist when ALDL is grounded with key on and engine not running, but may not be indicated by all makes of "Scan" testers.

If trouble codes are not present, this is not an indication that there is not a problem. Driveability related problems with codes displayed occur about 20 percent of the time, while driveability problems without codes occur about 80 percent of the time. Sensors that are out of specification WILL NOT set a trouble code but WILL cause driveability problems. Using a "Scan" tester is 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 tables in this article.

NOTE:

Information obtained by "Scan" tester is only as accurate as the tester itself. If erroneous voltage signals are suspected, it will be necessary to 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 ALDL test terminal. If same codes are not flashed by SERVICE ENGINE SOON light that were indicated by "Scan" tester, tester cannot be used on vehicle and information obtained by it will not be guaranteed accurate.

Buick Skylark Gran Sport 1990 - SCAN DATA

NOTE:

Information contained in the 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 every 1 1/4 seconds. On systems using P-4 computers, parameter updates are more often. Not all devices & systems are used on all models.

Buick Skylark Gran Sport 1990 PORT FUEL INJECTION

Tester Position	Units Measured	Nominal Data 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	3-4.5
Battery Voltage	Volts	13.5-14.5
Block Learn	Counts	118-138 (128 normal)
Canister Purge Sol.	On/Off	On/engine cold (idle some)
Clear Flood	On/Off	See tester manual
Coolant Fan	On/Off	Off below 216?F (102?C)
Coolant Temp.	C?	85-105? (norm. temperature)
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
INT (Integrator)	Counts	110-145 (128 normal)
Knock Retard (ESC)	Counts	0-255
Knock Signal	Yes/No	Yes when knock exists
MAT	C?	10-90?
MAP	Volts	1 (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 (auto.)
"	"	Spec. +/-50 RPM Neut. (man.)
Spark Advance	No. Deg.	Varies
TCC	On/Off	Off (On with command)
TPS	Volts	1.25 (idle) to 5.0 (WOT)
Throttle Angle	0-100%	0 (idle) to 100 (WOT)
Trouble Codes	Code #	No codes
Turbo Boost	On/Off	On when activated
Upshift Light (Man. Trans.)	On/Off	Off
VSS or MPH	MPH	0-Actual
Wastegate By-Pass	On/Off	On when by-passed
Water Injection	On/Off	On when injecting
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 Skylark Gran Sport 1990 - SUMMARY

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

Buick Skylark Gran Sport 1990 - DIAGNOSTIC TESTS

NOTE:

The following diagnostic flow charts and mini-schematics are supplied courtesy of General Motors Corp.

Buick Skylark Gran Sport 1990 - CODE 13, OPEN OXYGEN SENSOR CIRCUIT

NOTE:

Test numbers refer to test numbers on diagnostic chart.

1. The following conditions must exist to set a Code 13:
   • Engine running at least 40 seconds after start.
   • Engine coolant temperature greater than 108.5?F (42.5?C).
   • Code 21 or 22 must not be set.
   • Oxygen sensor voltage steady between .34 and .55 volt.
   • TPS signal greater than 6 percent for more time than less than 6% or about .3 volt greater than closed throttle voltage.
   • Conditions must be met and held for at least 20 seconds.
2. This test will indicate whether sensor is faulty, or if wiring and/or ECM is cause of Code 13.

   NOTE:

   Use only high impedance digital volt/ohmmeter for this test.

3. This test checks for continuity of circuits No. 412 and 413. If circuit No. 413 is open, ECM voltage on circuit No. 412 will be greater than .6 volt (600mV).

Buick Skylark Gran Sport 1990 - Diagnostic Aids

Normal scan voltage ranges between .1-1.0 volt (100-999 mV), while in "closed loop". Code 13 will set in 20 seconds if voltage remains between .35-.55 volt. System will go into "open loop" in about 15 seconds. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article.

Fig. 2: Buick Skylark Gran Sport 1990 - Component Locations - Code 13: Circuit Diagram (L & N BODIES)

Fig. 3: Buick Skylark Gran Sport 1990 - Component Locations - Code 13: Circuit Diagram (W BODY)

Fig. 4: Buick Skylark Gran Sport 1990 - Component Locations - Code 13: Flow Chart

Buick Skylark Gran Sport 1990 - CODE 14: COOLANT TEMP SENSOR SIGNAL VOLT LOW

1. Code 14 will be set if signal voltage indicates temperature greater than 285?F (140?C) and engine has been operating for more than 128 seconds.
2. This test will indicate if circuit No. 410 is shorted to ground and set a Code 14.

Buick Skylark Gran Sport 1990 - Diagnostic Aids

After engine is started, temperature should rise steadily to about 90?F (32?C), then stabilize when thermostat opens. If the engine is allowed to cool overnight, the coolant and MAT sensors should read close to each other when measured with a "Scan" tester. When Code 14 is set, ECM will turn on the cooling fan. The TEMPERATURE VS. RESISTANCE VALUES table (scale) may be used to test the coolant temperature sensor at various temperature levels. This enables an evaluation of a possible "shifted" (out of calibration) sensor. A shifted sensor could result in poor driveability complaints. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article.

Fig. 5: Buick Skylark Gran Sport 1990 - Component Locations - Code 14: Circuit Diagram (L BODY)

Fig. 6: Buick Skylark Gran Sport 1990 - Component Locations - Code 14: Circuit Diagram (N BODY)

Fig. 7: Buick Skylark Gran Sport 1990 - Component Locations - Code 14: Circuit Diagram (W BODY)

Fig. 8: Buick Skylark Gran Sport 1990 - Component Locations - Code 14: Flow Chart

Buick Skylark Gran Sport 1990 - CODE 15: COOLANT TEMP SENSOR SIGNAL VOLT HIGH

1. Code 15 will set if signal voltage indicates a coolant temperature less than -38?F (-39?C) for 60 seconds.
2. This test simulates conditions for a Code 14. If ECM recognizes low signal voltage and "Scan" tester indicates 130?C, ECM and wiring are okay.
3. This test will determine if circuit No. 410 is open. Five volts should be present at sensor connector if measured with DVOM.

Buick Skylark Gran Sport 1990 - Diagnostic Aids

After engine is started, temperature displayed by "Scan" tester should rise steadily to about 95?C, then stabilize when thermostat opens. It is normal for coolant temperature to fluctuate slightly around 95?C. Faulty connection or an open in either circuit can result in a Code 15. Codes 15, 21 and 66 stored at the same time could be result of an open sensor ground circuit. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article.

Fig. 9: Buick Skylark Gran Sport 1990 - Component Locations - Code 15: Circuit Diagram (L BODY)

Fig. 10: Buick Skylark Gran Sport 1990 - Component Locations - Code 15: Circuit Diagram (N BODY)

Fig. 11: Buick Skylark Gran Sport 1990 - Component Locations - Code 15: Circuit Diagram (W BODY)

Fig. 12: Buick Skylark Gran Sport 1990 - Component Locations - Code 15: Flow Chart

Buick Skylark Gran Sport 1990 - CODE 21: TPS SIGNAL VOLTAGE HIGH

1. The following conditions must be met to set a Code 21:
   • Engine running at operating temperature.
   • No Codes 33 or 34.
   • MAP less than 19.2 in. Hg (65 kPa).
   • TPS signal voltage greater than about 4 volts (78 percent).
   • Above conditions must exist for more than 5 seconds, or TPS voltage greater than about 4.7 volts.
2. With TPS unplugged, voltage should reduce to a lower value, if ECM and wiring are okay.
3. Probing ground circuit using a test light to battery voltage checks TPS ground circuit. An open or very high resistance ground will set a Code 21.

Buick Skylark Gran Sport 1990 - Diagnostic Aids

When using a "Scan" tester, throttle position should be displayed in voltage. Check TPS voltage with ignition on and engine off. At closed throttle display should read .4-.9 volt. Voltage should increase at a steady rate as throttle is opened toward wide open position. Some scan tools will display throttle angle in percentages (0=closed throttle and 100=wide open). An open ground circuit will set a Code 21. Codes 15, 21 and 66 stored simultaneously could be result of an open ground circuit. Check TPS connector for corrosion or improper connection. Check condition of connector seal and replace if necessary. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article.

Fig. 13: Buick Skylark Gran Sport 1990 - Component Locations - Code 21: Circuit Diagram (L BODY)

Fig. 14: Buick Skylark Gran Sport 1990 - Component Locations - Code 21: Circuit Diagram (N BODY)

Fig. 15: Buick Skylark Gran Sport 1990 - Component Locations - Code 21: Circuit Diagram (W BODY)

Fig. 16: Buick Skylark Gran Sport 1990 - Component Locations - Code 21: Flow Chart

Buick Skylark Gran Sport 1990 - CODE 22: TPS SIGNAL VOLTAGE LOW

1. In order for Code 22 to set, engine must be running and TPS signal voltage should be less than about .2 volt for 5 seconds.
2. This test simulates high voltage (Code 21). If ECM recognizes high signal voltage, ECM and wiring are okay.
3. TPS has an auto zeroing feature. If voltage is within range of .4-.9 volt, ECM will use that value as closed throttle. If voltage reading is out of zeroing range, TPS must be replaced.
4. A high voltage signal is simulated to check for an open in circuit No. 417.

Buick Skylark Gran Sport 1990 - Diagnostic Aids

When using a "Scan" tester, throttle position should be displayed in voltage. Check TPS voltage with ignition on and engine off. At closed throttle, display should read .49-.59 volt. Voltage should increase at a steady rate as throttle is opened toward wide open position. Some scan tools will display in percentages (0 percent=closed throttle and 100 percent=wide open). Codes 22, 33 and 66 stored simultaneously could be result of an open circuit No. 416. Check TPS connector for corrosion or improper connection. Check condition of connector seal, replace if necessary. See INTERMITTENTS in TESTS W/O CODES article if Code 22 is intermittent.

Fig. 17: Buick Skylark Gran Sport 1990 - Component Locations - Code 22: Circuit Diagram (L BODY)

Fig. 18: Buick Skylark Gran Sport 1990 - Component Locations - Code 22: Circuit Diagram (N BODY)

Fig. 19: Buick Skylark Gran Sport 1990 - Component Locations - Code 22: Circuit Diagram (W BODY)

Fig. 20: Buick Skylark Gran Sport 1990 - Component Locations - Code 22: Flow Chart

Buick Skylark Gran Sport 1990 - CODE 23: MAT SENSOR SIGNAL VOLTAGE HIGH

1. The following conditions must exists for a code 23 to set:
   • Signal voltage indicates manifold air temperature is less than -29?F (-34?C).
   • Engine has been running for at least 320 seconds.
   • Vehicle speed is less than 15 MPH.
2. Code 23 is set due to an open sensor, wire or connection. This test determines if wiring and ECM are okay.
3. This test indicates if signal circuit No. 472 or ground circuit is open.

Buick Skylark Gran Sport 1990 - Diagnostic Aids

"Scan" tester should display temperature of air entering engine close to ambient air temperature when engine is cold, and rise as underhood temperature increases. Improper connections or open sensor circuits can set Code 23. Codes 23 and 24 stored simultaneously, could be result of an open ground circuit. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article.

Fig. 21: Buick Skylark Gran Sport 1990 - Component Locations - Code 23: Circuit Diagram (L BODY)

Fig. 22: Buick Skylark Gran Sport 1990 - Component Locations - Code 23: Circuit Diagram (N BODY)

Fig. 23: Buick Skylark Gran Sport 1990 - Component Locations - Code 23: Circuit Diagram (W BODY)

Fig. 24: Buick Skylark Gran Sport 1990 - Component Locations - Code 23: Flow Chart

Buick Skylark Gran Sport 1990 - CODE 24: VEHICLE SPEED SENSOR

NOTE:

On vehicles with automatic transmission, a faulty or improperly adjusted park/neutral switch can result in a false Code 24. Use a "Scan" tester and check for proper signal while in Drive. - SYSTEMS & COMPONENT TESTING article in this section for P/N switch diagnosis.

1. Code 24 will set (with vehicle speed less than 2 MPH) only if the following conditions are met:
   • Engine RPM is between 1600 and 3600.
   • TPS is greater than 7 percent.
   • Gear selector not in Park or Neutral.
   • All conditions met for 20 seconds.
   • No Codes 21 or 22.

   Above conditions are met during road load deceleration. Ignore Code 24 sets when drive wheels are not turning faster than 3 MPH. PM generator only produces a signal if drive wheels are turning greater than 3 MPH.

2. Ensure correct MEM-CAL is used before replacing ECM.

Buick Skylark Gran Sport 1990 - Diagnostic Aids

A problem in circuit No. 434 (auto. trans.) will not affect VSS input or readings displayed by "Scan" tester. Ensure circuits No. 400 and 401 have proper connections. Also check for correct harness routing. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article.

Fig. 25: Buick Skylark Gran Sport 1990 - Component Locations - Code 24: Circuit Diagram (L & N BODIES)

Fig. 26: Buick Skylark Gran Sport 1990 - Component Locations - Code 24: Circuit Diagram (W BODY)

Fig. 27: Buick Skylark Gran Sport 1990 - Component Locations - Code 24: Flow Chart

Buick Skylark Gran Sport 1990 - CODE 25: MAT SENSOR SIGNAL VOLTAGE LOW

1. Code 25 will set only if signal voltage indicates manifold air temperature greater than about 318?F (159?C) and if vehicle speed is greater than 15 MPH.

Buick Skylark Gran Sport 1990 - Diagnostic Aids

Use temperature scale to check MAT resistances. This scale should be used to eliminate the possibility of a sensor which is out of calibration. A out-of-calibration sensor could be the cause of poor driveability. See INTERMITTENTS in TESTS W/O CODES article if code is intermittent.

Fig. 28: Buick Skylark Gran Sport 1990 - Component Locations - Code 25: Circuit Diagram (L BODY)

Fig. 29: Buick Skylark Gran Sport 1990 - Component Locations - Code 25: Circuit Diagram (N BODY)

Fig. 30: Buick Skylark Gran Sport 1990 - Component Locations - Code 25: Circuit Diagram (W BODY)

Fig. 31: Buick Skylark Gran Sport 1990 - Component Locations - Code 25: Flow Chart

Buick Skylark Gran Sport 1990 - CODE 26: QUAD-DRIVER ERROR (L & N BODIES)

The ECM controls most components with electronic switches completing a ground circuit when actuated. These switches are arranged in groups of 4, called Quad-Driver Modules (QDMs), which can independently control up to 4 outputs (ECM terminals). When an output is actuated, the terminal is grounded and its voltage normally will be low. When an output is off, its terminal voltage will normally be high, except for the Torque Converter Clutch (TCC), which depends on the brake switch and 2nd gear TCC switch.

QDMs are fault protected. If a relay or solenoid coil is shorted, having very low resistance, or if control side of circuit is shorted to voltage, it would allow too much current into QDM. The QDM senses this and turns the output off, or its internal resistance increases to limit current flow and protect the QDM. The result is high output terminal voltage when it should be low. If the circuit from battery voltage or the component is open, or the control side of circuit is shorted to ground, terminal voltage will be low, even when output is turned off. Either of these conditions is considered to be a QDM fault.

Each QDM has a separate fault line to indicate the presence of a current fault to ECM's central processor. A "Scan" tester displays the status of each of these fault lines as "low equals okay" or "high equals fault".

Because of the brake and 2nd gear switches in the TCC circuit, Code 26 is set under different conditions for QDM A and QDM B. Those conditions are as described:

• QDM A fault line equals "high" for 20 seconds or more.

On automatic transaxle

• QDM B fault line equals "high" for 20 seconds or more.
• Brake switch signal indicates switch is closed.
• Second gear switch indicates transaxle is in 2nd or 3rd gear.
• TCC is commanded on.

NOTE:

QDM B fault line on an automatic transaxle vehicle will normally be "high" when the vehicle is stopped. The ECM ignores the QDM B fault line except under conditions noted above.

Buick Skylark Gran Sport 1990 - Diagnostic Aids

Intermittent faults must be continuously present for at least 20 seconds to cause Code 26 to set. QDM controlled circuits should be inspected for poor terminal contact or damaged harness. The TCC circuit should be checked with the transaxle at operating temperature if Code 26 sets intermittently and no other cause is found, as a defective TCC solenoid resistance can drop too low (below 20 ohms) at high temperature. QDM faults can be detected as noted above and when outputs are on or off as follows:

• Open circuit or control circuit short to ground-output commanded off.
• Shorted device or control circuit short to voltage-output commanded on.

Fig. 32: Buick Skylark Gran Sport 1990 - Component Locations - Code 26: Circuit Diagram (L BODY)

Fig. 33: Buick Skylark Gran Sport 1990 - Component Locations - Code 26: Circuit Diagram (N BODY)

Fig. 34: Buick Skylark Gran Sport 1990 - Component Locations - Code 26: Flow Chart (1 of 3)

Fig. 35: Buick Skylark Gran Sport 1990 - Component Locations - Code 26: Flow Chart (2 of 3)

Fig. 36: Buick Skylark Gran Sport 1990 - Component Locations - Code 26: Flow Chart (3 of 3)

Buick Skylark Gran Sport 1990 - CODE 26, QUAD-DRIVER ERROR (W BODY)

The ECM controls most components with electronic switches completing a ground circuit when actuated. These switches are arranged in groups of 4, called Quad-Driver Modules (QDM's), which can independently control up to 4 outputs (ECM terminals). When an output is actuated, the terminal is grounded and its voltage normally will be low. When an output is off, its terminal voltage normally will be high, except for the TCC, which depends on the brake and 2nd gear TCC switches.

QDM's are fault protected. If a relay or solenoid coil is shorted, having very low resistance, or if control side of circuit is shorted to voltage, it would allow too much current into QDM. The QDM senses this and turns the output off, or its internal resistance increases to limit current flow and protect the QDM. The result is high output terminal voltage when it should be low. If the circuit from battery voltage or the component is open, or the control side of circuit is shorted to ground, terminal voltage will be low, even when output is turned off. Either of these conditions is considered to be a QDM fault.

The ECM ignores the fault line signal from QDM 3 to prevent false setting of Code 26 due to brake or 2nd gear TCC series switches. As a result, QDM 3 circuit problems will not cause a Code 26 although the circuits are fault protected and operate the same as QDMs 1 and 2.

Fig. 37: Buick Skylark Gran Sport 1990 - Component Locations - Code 26: Circuit Diagram For 1 of 3 (W BODY)

Fig. 38: Buick Skylark Gran Sport 1990 - Component Locations - Code 26: Flow Chart (1 of 3)

Fig. 39: Buick Skylark Gran Sport 1990 - Component Locations - Code 26: Flow Chart (2 of 3)

Fig. 40: Buick Skylark Gran Sport 1990 - Component Locations - Code 26: Circuit Diagram For 3 of 3 (W BODY)

Fig. 41: Buick Skylark Gran Sport 1990 - Component Locations - Code 26: Flow Chart (3 of 3)

Buick Skylark Gran Sport 1990 - CODE 32, EGR SYSTEM FAULT (W BODY)

NOTE:

Test numbers refer to test numbers on diagnostic chart.

1. Code 26 indicates an electrical problem is likely. This can be diagnosed using the Code 26 chart.
2. This step actuates each solenoid and should result in a momentary drop in RPM or engine roughness if the EGR flows at idle. The No. 2 solenoid should have more effect than the No. 1 solenoid.

Buick Skylark Gran Sport 1990 - Diagnostic Aids

See INTERMITTENTS in TESTS W/O CODES article in this section if code is intermittent.

Fig. 42: Buick Skylark Gran Sport 1990 - Component Locations - Code 32: Circuit Diagram (W Body)

Fig. 43: Buick Skylark Gran Sport 1990 - Component Locations - Code 32: Flow Chart (W Body)

Buick Skylark Gran Sport 1990 - CODE 33, MAP SENSOR SIGNAL VOLTAGE HIGH

NOTE:

Test numbers refer to test numbers on diagnostic chart.

1. The following conditions must be met to set a Code 33:
   • MAP signal greater than 80 kPa.
   • TPS reading below 12 percent.
   • VSS reading below one MPH.
   • Above conditions met for 5 seconds.
2. With MAP sensor unplugged, ECM MAP signal voltage should be low if ECM and wiring are okay.

Buick Skylark Gran Sport 1990 - Diagnostic Aids

An intermittent open in MAP/MAT ground circuit can result in Code 33. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

Fig. 44: Buick Skylark Gran Sport 1990 - Component Locations - Code 33: Circuit Diagram (L Body)

Fig. 45: Buick Skylark Gran Sport 1990 - Component Locations - Code 33: Circuit Diagram (N Body)

Fig. 46: Buick Skylark Gran Sport 1990 - Component Locations - Code 33: Circuit Diagram (W Body)

Fig. 47: Buick Skylark Gran Sport 1990 - Component Locations - Code 33: Flow Chart

Buick Skylark Gran Sport 1990 - CODE 34: MAP SENSOR SIGNAL VOLTAGE LOW

1. The following conditions must be met to set a Code 34:
   • Engine running at operating temperature.
   • No Code 21.
   • MAP reading less than 14 kPa.
   • Engine RPM less than 1200 or TPS greater than 15.2 percent.
   • Above conditions met for .2 second.
2. This test checks for sensor being at fault for low voltage, or if there is an ECM or wiring problem.
3. This test simulates high signal voltage to check for open in circuit No. 432. If test light is bright during this test, circuit No. 432 is probably shorted to ground. If "Scan" tester reads greater than 4 volts at this test, 5-volt reference circuit can be checked by measuring voltage at MAP sensor terminal "C". Reading should be 5 volts.

Buick Skylark Gran Sport 1990 - Diagnostic Aids

An intermittent in the 5-volt reference or ground circuit will result in a Code 34. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

Fig. 48: Buick Skylark Gran Sport 1990 - Component Locations - Code 34: Circuit Diagram (L Body)

Fig. 49: Buick Skylark Gran Sport 1990 - Component Locations - Code 34: Circuit Diagram (N Body)

Fig. 50: Buick Skylark Gran Sport 1990 - Component Locations - Code 34: Circuit Diagram (W Body)

Fig. 51: Buick Skylark Gran Sport 1990 - Component Locations - Code 34: Flow Chart

Buick Skylark Gran Sport 1990 - CODE 35: IAC IDLE SPEED ERROR

This code is intended to detect intake vacuum leaks. The following conditions must be met to set a Code 35:

• Engine speed at least 175 RPM more or less than specification.
• TPS signal voltage indicates throttle position less than one percent.
• VSS indicates vehicle speed is less than 3 MPH.
• Above conditions are met for at least 5 seconds and IAC counts are less than 10.

NOTE:

Test numbers refer to test numbers on diagnostic chart.

1. The IAC tester extends or retracts the IAC valve. Valve movement is verified by an RPM change. If engine speed doesn't change, valve can be retested after removal from throttle body.
2. This step checks IAC movement quality. Between 700-1500 RPM, engine speed should change smoothly with each tester light flash in both extend and retract. If IAC valve is retracted beyond control range (about 1500 RPM), it may take many flashes in the extend position before engine speed begins to drop. This is normal on certain engines. Fully extending IAC may cause engine stall. This is normal.

Buick Skylark Gran Sport 1990 - Diagnostic Aids

Always check for vacuum leaks caused by disconnected lines, brittle hoses, cuts or improper connections. Check throttle body and manifold gaskets for proper sealing. Also check for cracked intake manifold. Ensure TPS and MAP sensor are operating properly. Compare with components from a known good vehicle if necessary. Check for opens, shorts or poor connections in the IAC driver circuit wiring or faulty connections at ECM terminals. These wiring problems can cause improper idle control and may cause a Code 35. If IAC valve is stopped in an open position and can't respond to ECM, or minimum air rate throttle stop screw is set too high, Code 35 could result. If no problem is found and Code 35 resets, replace ECM.

Fig. 52: Buick Skylark Gran Sport 1990 - Component Locations - Code 35: Circuit Diagram (L Body)

Fig. 53: Buick Skylark Gran Sport 1990 - Component Locations - Code 35: Circuit Diagram (N Body)

Fig. 54: Buick Skylark Gran Sport 1990 - Component Locations - Code 35: Circuit Diagram (W Body)

Fig. 55: Buick Skylark Gran Sport 1990 - Component Locations - Code 35: Flow Chart

Buick Skylark Gran Sport 1990 - CODE 41: 1X REFERENCE CIRCUIT

The ignition module sends a signal to ECM once per revolution to indicate crankshaft position. The ECM uses this information to determine when to pulse injectors for cylinders No. 2 and 3. This signal can be described as a synchronization signal and is called 1X reference, because it occurs one time per revolution.

The ignition module applies 5 volts from terminal "G" through circuit to ECM terminal "BC5" (L & N Body) or "C11" (W Body) and in effect, switches this circuit to ground for a short period of time, 125 degrees before TDC of cylinders No. 2 and 3. Code 41 is set if ECM receives (8) 2X reference pulses without a 1X reference pulse. When Code 41 is present, ECM pulses injectors in the simultaneously mode.

NOTE:

Test numbers refer to test numbers on diagnostic chart.

1. This determines if ECM recognizes a fault. If a Code 41 is not set here, problem is intermittent and could be caused by a loose connection.
2. This step simulates 1X signal. If circuit and ECM are okay, ECM should recognize the voltage drop as test light probe is removed. This step will only give accurate results if:
   • Chart sequence is used (ignition off or ignition on).
   • "Scan" tester is set to 1X reference.
   • Terminal "G" is contacted using test light probe.

   The ECM will only recognize up to 4 simulated 1X pulses under this test condition.

3. If ECM did not recognize simulation of 1X signal, circuit No. 969 (L and W bodies) or No. 647 (N body) may be open or shorted to ground or voltage. If circuit is okay, ECM is faulty.
4. Step 2 indicated 1X circuit is okay and ECM is capable of recognizing simulated 1X reference pulse. This indicates either a poor connection at ignition module terminal "G" or a faulty ignition module caused Code 41 to occur.

Buick Skylark Gran Sport 1990 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Inspect ECM harness 1X connector terminal and ignition module terminal "G" for improperly formed or damaged terminals, poor terminal to wire connection and damaged harness. Code 41 will set if a 1988 ignition module is installed.

Fig. 56: Buick Skylark Gran Sport 1990 - Component Locations - Code 41: Circuit Diagram (L Body)

Fig. 57: Buick Skylark Gran Sport 1990 - Component Locations - Code 41: Circuit Diagram (N Body)

Fig. 58: Buick Skylark Gran Sport 1990 - Component Locations - Code 41: Circuit Diagram (W Body)

Fig. 59: Buick Skylark Gran Sport 1990 - Component Locations - Code 41: Flow Chart

Buick Skylark Gran Sport 1990 - CODE 42: ELECT SPART TIMING CIRCUIT OPEN OR GND

1. Checks if ECM recognizes a fault. If a Code 42 is not set here, an intermittent problem exists and could be caused by a loose connection.
2. With ECM disconnected, ohmmeter should indicate less than 500 ohms, which is normal resistance for the ignition module. A higher resistance indicates a fault in circuit No. 423, poor ignition module connection or faulty ignition module.
3. If test light was illuminated when connected from 12 volts to ECM harness by-pass terminal either circuit No. 423 is shorted to ground or ignition module is faulty.
4. Checks if ignition module switches when bypass circuit is energized by 12 volts through test light. If ignition module switches, ohmmeter reading should shift to greater than 8000 ohms.
5. Disconnecting ignition module should cause ohmmeter to indicate as if it were monitoring an open circuit (infinite reading). If ohmmeter reads anything other than infinity, circuit No. 423 is shorted to ground.

Buick Skylark Gran Sport 1990 - Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or wire broken inside insulation. Inspect ECM harness connectors for backed-out by-pass or EST terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection or damaged harness.

Fig. 60: Buick Skylark Gran Sport 1990 - Component Locations - Code 42: Circuit Diagram (L Body)

Fig. 61: Buick Skylark Gran Sport 1990 - Component Locations - Code 42: Circuit Diagram (N Body)

Fig. 62: Buick Skylark Gran Sport 1990 - Component Locations - Code 42: Circuit Diagram (W Body)

Fig. 63: Buick Skylark Gran Sport 1990 - Component Locations - Code 42: Flow Chart

Buick Skylark Gran Sport 1990 - CODE 43: ELECT SPARK CONTROL RETARD SIGNAL TO LOW

Code 43 indicates the ECM has seen high or low voltage at circuit No. 496 for longer than 5 seconds with the engine running.

NOTE:

Test numbers refer to test numbers on diagnostic chart.

1. If conditions for test as described above are being met, Code 43 will currently set and the "SES" light will be illuminated.
2. The ECM has a 5-volt pull-up resistor, which should be present at the knock sensor terminal.
3. This test determines if internal resistance of knock sensor is within an acceptable range.

Buick Skylark Gran Sport 1990 - Diagnostic Aids

Check circuit No. 496 for a potential short or open to ground. Also check for proper installation of MEM-CAL. Mechanical engine knock can cause a knock sensor signal. Abnormal engine noise must be corrected before using this chart.

NOTE:

Code 43 circuit diagram and flow chart has been updated by Technical Service Bulletin No. 91-6-6, dated 8/24/90.

Fig. 64: Buick Skylark Gran Sport 1990 - Component Locations - Code 43: Circuit Diagram (L Body)

Fig. 65: Buick Skylark Gran Sport 1990 - Component Locations - Code 43: Circuit Diagram (N Body)

Fig. 66: Buick Skylark Gran Sport 1990 - Component Locations - Code 43: Circuit Diagram (W Body)

Fig. 67: Buick Skylark Gran Sport 1990 - Component Locations - Code 43: Flow Chart

Buick Skylark Gran Sport 1990 - CODE 44: LEAN EXHAUST INDICATED

1. The following conditions must be met to set a Code 44 when signal voltage is present on circuit No. 412:
   • Value remains less than .3 volt for at least 50 seconds.
   • System is operating in "closed loop".
   • No Code 33 or 34.
   • "Closed loop" integrator active.
   • TPS signal greater than 5 percent.

Buick Skylark Gran Sport 1990 - Diagnostic Aids

Code 44 or lean exhaust is most likely caused by one of following:

• Fuel Pressure - System will be lean if pressure is too low. It may be necessary to monitor fuel pressure, while driving vehicle at various road speeds and/or loads, to confirm condition.
• MAP Sensor - An output causes ECM to sense a lower than normal manifold pressure (high vacuum) can cause system to operate lean. Disconnecting MAP sensor will allow ECM to substitute a fixed (default) value for MAP sensor. If rich condition discontinues when sensor is disconnected, substitute using a known good sensor and recheck.
• Fuel Contamination - Water, even in small amounts, near in-tank fuel pump inlet can be delivered to injector(s). Water delivered to injector(s) causes lean exhaust and may set a Code 44.
• Sensor Harness - Sensor pigtail may be mispositioned and contacting exhaust manifold.
• Engine Misfire - A cylinder misfire will result in unburned fuel mixture in the exhaust, which may set a Code 44.

Also check for a cracked O2 sensor or a plugged fuel filter.

Fig. 68: Buick Skylark Gran Sport 1990 - Component Locations - Code 44: Circuit Diagram (L & N Body)

Fig. 69: Buick Skylark Gran Sport 1990 - Component Locations - Code 44: Circuit Diagram (W Body)

Fig. 70: Buick Skylark Gran Sport 1990 - Component Locations - Code 44: Flow Chart

Buick Skylark Gran Sport 1990 - CODE 45: RICH EXHAUST INDICATED

1. The following conditions must be met to set a Code 45:
   • O2 sensor voltage is greater than .75 volt.
   • No Code 33 or 34.
   • Fuel system in "closed loop".
   • TPS greater than 5 percent.
   • Above conditions met for 50 seconds.

Buick Skylark Gran Sport 1990 - Diagnostic Aids

Code 45 or rich exhaust is most likely cause by one or a combination of the following conditions:

• Fuel Pressure - Engine will operate in a rich condition if fuel pressure is to high. ECM can compensate for some increase. If increase is greater than a certain value a Code 45 will be set.
• Leaking Injectors - Check for leaking injector(s).
• HEI Shielding - Check Integrated Direct Ignition (IDI) shielding. An open ground circuit No. 453 may result in induced electrical noise. The ECM may see this noise as distributor pulses and richen mixture. Engine tachometer will indicate a higher than actual engine speed, which can aid in diagnosing problem.
• Canister Purge - Check canister purge for fuel saturation. If fuel saturation is present, check control and hoses.
• Map Sensor - A higher than normal MAP sensor output (low vacuum) can cause ECM to richen mixture. Unplugging MAP sensor will allow ECM to set a fixed value for MAP sensor. Check for cracked or punctured hose. Replace MAP sensor with a known good sensor and check for rich condition. If condition disappears, replace MAP sensor.
• Pressure Regulator - Check pressure regulator for lack of pressure retention. Check diaphragm by inspecting vacuum line for liquid (raw) fuel.
• TPS - An intermittent TPS output can cause a rich condition. This is due to false engine acceleration indication.
• Oxygen Sensor Contamination - Check O2 sensor for contamination from fuel or use of improper RTV sealant. O2 sensor may have White powdery coating and result in a high, but false signal voltage (rich indication). ECM will then reduce fuel delivery to engine causing a severe surge driveability problem.

Fig. 71: Buick Skylark Gran Sport 1990 - Component Locations - Code 45: Circuit Diagram (L & N Body)

Fig. 72: Buick Skylark Gran Sport 1990 - Component Locations - Code 45: Circuit Diagram (W Body)

Fig. 73: Buick Skylark Gran Sport 1990 - Component Locations - Code 45: Flow Chart

Buick Skylark Gran Sport 1990 - CODE 51: FAULTY MEM-CAL

This code indicates a faulty or incorrect MEM-CAL. Ensure all pins are properly inserted in socket and MEM-CAL is correctly latched. If okay, replace MEM-CAL, clear memory and recheck. If Code 51 reappears, replace ECM.

NOTE:

To prevent possible electrostatic discharge damage to the ECM or MEM-CAL, DO NOT touch the component leads. DO NOT remove the integrated circuit from carrier.

Buick Skylark Gran Sport 1990 - CODE 53 FAULTY ALTERNATOR - VOLTAGE HIGH

A Code 53 will set, if ECM terminal voltages are more than 17.1 volts for about .2 second, with ignition on. During this time when failure is present, all ECM outputs will be disengaged. Additional codes may result.

NOTE:

Test numbers refer to test numbers on diagnostic chart.

1. Battery output should be between 10-17 volts.
2. This tests if voltage reading is due to alternator or ECM. With engine running, check battery voltage. If reading is greater than 17.1 volts, ECM is okay.
3. This step checks for faulty alternator under load condition. If voltage is greater than 17.1 volts, diagnose and service alternator.

Fig. 74: Buick Skylark Gran Sport 1990 - Component Locations - Code 53: Circuit Diagram (L Body)

Fig. 75: Buick Skylark Gran Sport 1990 - Component Locations - Code 53: Circuit Diagram (N Body)

Fig. 76: Buick Skylark Gran Sport 1990 - Component Locations - Code 53: Circuit Diagram (W Body)

Fig. 77: Buick Skylark Gran Sport 1990 - Component Locations - Code 53: Flow Chart

Buick Skylark Gran Sport 1990 - CODE 62: GEAR SWITCH ERROR (N BODY)

NOTE:

Code 62 has been revised for some models. Before proceeding with any further testing see appropriate TSB's under symptoms of CHECK ENGINE LIGHT.

Code 62 is used to check 2nd and 3rd gear switch inputs to ECM. In order to determine transmission gear input signals to ECM, see INPUT SIGNALS table.

Buick Skylark Gran Sport 1990 INPUTS SIGNALS

Gear Position	Switch Position
1st (Also P/N & R)	2nd Closed
"	3rd Open
2nd	2nd Open
"	3rd Open
3rd	2nd Open
"	3rd Closed

NOTE:

Test numbers refer to test numbers on diagnostic chart.

1. If the following conditions are met for about 17 seconds, a Code 62 will be set:
   • In Park or Neutral and 2nd or 3rd gear indicated.
   • Vehicle speed less than about 5 MPH, and 2nd or 3rd gear indicated.
   • First or 2nd gear indicated. Less than about 3000 RPM. Gear selector not in Park or Neutral, and VSS greater than 50 MPH.

   First step checks for an open or grounded circuit between transmission connector and ECM. Since ECM terminals are normally high, battery voltage should be indicated at both terminals with connector removed.

2. Digital voltmeter should measure zero volt at terminal "B" because 3rd gear switch should be open, providing no continuity to ground. Terminal "C" should measure near battery voltage because 2nd gear switch should provide continuity to ground.
3. This tests normal transmission switch function. In 3rd gear, both switches should have changed from their original 1st gear state.

Buick Skylark Gran Sport 1990 - Diagnostic Aids

Clear codes and recheck for Code 62. If code resets, check all harness connections, VSS, RPM, P/N circuits prior to replacing ECM. Transmission starting in 2nd or 3rd gear, or a sticking 2nd gear switch can also set a Code 62.

Fig. 78: Buick Skylark Gran Sport 1990 - Component Locations - Code 62: Circuit Diagram (N Body)

Fig. 79: Buick Skylark Gran Sport 1990 - Component Locations - Code 62: Flow Chart (N Body)

Buick Skylark Gran Sport 1990 - CODE 62, GEAR SWITCH ERROR (W BODY)

NOTE:

Code 62 has been revised for some models. Before proceeding with any further testing see appropriate TSB's under symptoms of CHECK ENGINE LIGHT.

Code 62 is used to check 2nd and 3rd gear switch inputs to ECM. In order to determine transmission gear input signals to ECM, see INPUT SIGNALS table.

Buick Skylark Gran Sport 1990 INPUTS SIGNALS

Gear Position	Switch Position
1st (Also P/N & R)	2nd Closed
"	3rd Closed
2nd	2nd Open
"	3rd Closed
3rd	2nd Open
"	3rd Open

NOTE:

Test numbers refer to test numbers on diagnostic chart.

1. If the following conditions are met for about 17 seconds, a Code 62 will be set:
   • In Park or Neutral and 2nd or 3rd gear indicated.
   • Vehicle speed less than about 5 MPH, and 2nd or 3rd gear indicated.
   • First or 2nd gear indicated. Less than about 3000 RPM. Gear selector not in Park or Neutral, and VSS greater than 50 MPH.

   First step checks for an open or grounded circuit between transmission connector and ECM. Since ECM terminals are normally high, battery voltage should be indicated at both terminals with connector removed.

2. Digital voltmeter should measure near battery voltage because 2nd and 3rd gear switches should provide continuity to ground.
3. This tests normally transmission switch function. In 3rd gear, both switches should have changed from their original 1st gear state.

Buick Skylark Gran Sport 1990 - Diagnostic Aids

Clear codes and recheck for Code 62. If code resets, check all harness connections, VSS, RPM, P/N circuits prior to replacing ECM. Transmission starting in 2nd or 3rd gear can also set a Code 62.

Fig. 80: Buick Skylark Gran Sport 1990 - Component Locations - Code 62: Circuit Diagram (W Body)

Fig. 81: Buick Skylark Gran Sport 1990 - Component Locations - Code 62: Flow Chart (W Body)

Buick Skylark Gran Sport 1990 - CODE 65, INJECTOR CURRENT LOW (L & N BODIES)

The ECM has 2 injector driver circuits, each controlling a pair of injectors (1 and 4, or 2 and 3). The ECM monitors current of each injector driver circuit by measuring voltage drop through a fixed resistor. The ECM is able to control voltage drop. The current through each driver is allowed to rise to a peak of 4 amps, enabling injectors to open quickly, and is then reduced to one amp, holding them open. This is called, "peak and hold". If current can't reach a 4-amp peak, Code 65 is set. This code is also set if an injector driver circuit is shorted to voltage.

NOTE:

Test numbers refer to test numbers on diagnostic chart.

1. The following conditions must be present to set a Code 65:
   • The 4-amp injector current was not reached on each circuit.
   • Battery voltage greater than 9 volts.
   • Injectors pulsed "ON" longer than calibrated pulse width.
   • The above conditions met for 20 seconds.
2. Checks ECM and harness wiring to 3-terminal injector harness connector.
3. This tests for open injector harness or injector.

   NOTE:

   Although shorted harness or injector will not set a Code 65, problem should be corrected if discovered.

4. Results of step 2) will determine which branch to follow on Code 65 flow chart (2 of 2).
5. Each harness was confirmed as being okay in steps 2) and 3). This test will check remainder of circuit from injectors to ECM.
6. Identifies cause of high resistance found in step 3). A short or low resistance will not cause Code 65, but should be corrected.
7. This tests for grounded "peak and hold" jumpers. This condition would allow injectors to pulse, but would NOT allow "peak and hold" operation as current would not flow through resistor in ECM.
8. This checks for short to voltage in injector driver circuits. Engine must be cranked to ensure voltage to circuit No. 120.
9. Determines if injector driver circuits No. 467 and No. 468 are shorted to ground.
10. This checks the output at the ECM to determine if circuits No. 467 and 468 are okay.
11. Checks for proper continuity of "peak and hold" jumpers circuits.

Buick Skylark Gran Sport 1990 - Diagnostic Aids

An open in injector drive or "peak and hold" circuits, or circuits No. 467 or No. 468 shorted to voltage will cause a Code 65 to be set and also cause misfire due to an inoperative pair of injectors. "Peak and hold" circuits shorted to ground will cause a Code 65 to set, while allowing injectors to pulse. An intermittent problem would have to be present for at least 20 seconds to set Code 65.

Fig. 82: Buick Skylark Gran Sport 1990 - Component Locations - Code 65: Circuit Diagram (L Body)

Fig. 83: Buick Skylark Gran Sport 1990 - Component Locations - Code 65: Circuit Diagram (N Body)

Fig. 84: Buick Skylark Gran Sport 1990 - Component Locations - Code 65: Flow Chart (1 of 2)

Fig. 85: Buick Skylark Gran Sport 1990 - Component Locations - Code 65: Flow Chart (2 of 2)

Buick Skylark Gran Sport 1990 - CODE 65, INJECTOR CURRENT LOW W BODY

The ECM has 2 injector driver circuits, each controlling a pair of injectors (1 and 4, or 2 and 3). The ECM monitors current of each injector driver circuit by measuring voltage drop through a fixed resistor. The ECM is able to control voltage drop. The current through each driver is allowed to rise to a peak of 4 amps, enabling injectors to open quickly, and is then reduced to one amp, holding them open. This is called "peak and hold". If current can't reach a 4-amp peak, Code 65 is set. This code is also set if an injector driver circuit is shorted to voltage.

NOTE:

Test numbers refer to test numbers on diagnostic chart.

1. The following conditions must be present to set a Code 65:
   • The 4-amp injector current was not reached on each circuit.
   • Battery voltage greater than 9 volts.
   • Injectors pulsed "ON" longer than calibrated pulse width.
   • The above conditions met for 20 seconds.
2. Checks ECM and harness wiring to 3-terminal injector harness connector.
3. This tests for open injector harness or injector.

   NOTE:

   Although shorted harness or injector will not set a Code 65, problem should be corrected if discovered.

4. Results of step 2) will determine which branch to follow on Code 65 flow chart (2 of 2).
5. Each harness was confirmed as being okay in steps 2) and 3). This test will check remainder of circuit from injectors to ECM.
6. Identifies cause of high resistance found in step 3). A shorted injector will cause Code 65.
7. This tests for grounded "peak and hold" jumpers. This condition allows injectors to pulse, but would not allow "peak and hold" operation as current would not flow through resistor in ECM.
8. This checks for short to voltage in injector driver circuits.
9. Determines if injector driver circuits No. 467 and 468 are shorted to ground.
10. This checks the output at the ECM to determine if circuits No. 467 and 468 are okay.
11. Checks for proper continuity of "peak and hold" jumpers circuits No. 887 and No. 888.

Buick Skylark Gran Sport 1990 - Diagnostic Aids

Check injector and ECM harness for damage or being pinched. A shorted injector will cause Code 65 and a cylinder misfire. An open or short to voltage in an injector drive circuit between the injector and the ECM or in a "peak and hold" jumper will cause Code 65 and a severe misfire. A short to ground in an injector driver circuit between the injectors and the ECM will also cause a Code 65 and a severe misfire due to a pair of injectors being open continuously. A short to ground on a "peak and hold" jumper will cause a Code 65 without noticeable effect on engine performance.

Fig. 86: Buick Skylark Gran Sport 1990 - Component Locations - Code 65: Circuit Diagram (W Body)

Fig. 87: Buick Skylark Gran Sport 1990 - Component Locations - Code 65: Flow Chart (1 of 2)

Fig. 88: Buick Skylark Gran Sport 1990 - Component Locations - Code 65: Flow Chart (2 of 2)

Buick Skylark Gran Sport 1990 - CODE 66, A/C PRESSURE SENSOR VOLT OUT OF SPEC (L & N BODIES)

The A/C pressure sensor responds to changes in A/C refrigerant system high side pressure. ECM uses this information to determine load placed on engine during A/C compressor operation and IAC valve position for idle speed control. A 5-volt reference signal and ground are both provided by ECM. A signal line is also provided to the ECM. The signal received by ECM is proportional to A/C system pressure. Operational range of the sensor is 0-450 psi (or about .1-4.9 volts). If voltage falls outside calibrated range for 5 seconds or more, a Code 66 will be set. A/C compressor is disabled by the ECM when a Code 66 is set.

NOTE:

Test numbers refer to test numbers on diagnostic chart.

1. This tests voltage signal being received by ECM from A/C pressure sensor.
2. This tests if high voltage signal is caused by shorted sensor or short to voltage in circuit. Normally, unplugging sensor would cause a normal circuit to reduce to near zero volts.
3. Determines if low voltage is from sensor or circuit. This is done by jumpering 5 volts to sensor signal circuit No. 380. This checks circuit, connections and ECM.
4. Since the prior step eliminated pressure switch, this tests if low voltage signal was caused by an open in sensor circuit or 5-volt reference circuit.

Buick Skylark Gran Sport 1990 - Diagnostic Aids

Code 66 sets when signal voltage falls outside the normal sensor range and is not due to a refrigerant system problem. If problem is intermittent, check for opens or shorts in harness or poor connections. If okay, replace A/C pressure sensor. If Code 66 resets again, replace ECM.

NOTE:

Code 66 will set on non-A/C vehicles if circuit No. 450 to terminal "BC3" is open or shorted to battery voltage.

Fig. 89: Buick Skylark Gran Sport 1990 - Component Locations - Code 66: Circuit Diagram (L Body)

Fig. 90: Buick Skylark Gran Sport 1990 - Component Locations - Code 66: Circuit Diagram (N Body)

Fig. 91: Buick Skylark Gran Sport 1990 - Component Locations - Code 66: Flow Chart

Buick Skylark Gran Sport 1990 - CODE 66: A/C PRESSURE SENSOR VOLT OUT OF SPEC (W BODY)

The A/C pressure sensor responds to changes in A/C refrigerant system high side pressure. ECM uses this information to determine load placed on the engine during A/C compressor operation and IAC valve position for idle speed control. A 5-volt reference signal and ground are both provided by ECM. A signal line is also provided to the ECM. The signal received by ECM is proportional to A/C system pressure. Operational range of the sensor is 0-450 psi (or about .1-4.9 volts). If voltage falls outside calibrated range for 5 seconds or more, a Code 66 will set. A/C compressor is disabled by the ECM when a Code 66 is set.

NOTE:

Test numbers refer to test numbers on diagnostic chart.

1. This tests voltage signal being received by ECM from A/C pressure sensor.
2. This tests if high voltage signal is caused by shorted sensor or short to voltage in circuit. Normally, unplugging sensor would cause a normal circuit to reduce to near zero volts.
3. Determines if low voltage is from sensor or circuit. This is done by jumpering 5 volts to sensor signal circuit No. 732 volts. This checks circuit, connections and ECM.
4. Since the prior step eliminated pressure switch, this tests if low voltage signal was caused by an open in sensor circuit or 5-volt reference circuit.

Buick Skylark Gran Sport 1990 - Diagnostic Aids

Code 66 sets when signal voltage falls outside the normal sensor range and is not due to a refrigerant system problem. If problem is intermittent, check for opens or shorts in harness or poor connections. If okay, replace A/C pressure sensor. If Code 66 resets again, replace ECM.

Fig. 92: Buick Skylark Gran Sport 1990 - Component Locations - Code 66: Circuit Diagram (W Body)

Fig. 93: Buick Skylark Gran Sport 1990 - Component Locations - Code 66: Flow Chart