Buick Riviera 1990 - 1990 ENGINE PERFORMANCE General Motors Self-Diagnostics - BCM Tests

Buick Riviera 1990 - ENTERING SELF-DIAGNOSTICS IPC SEGMENT CHECK

1. Turn ignition switch to the ON position. Simultaneously depress OFF and WARM buttons on the Electronic Climate Control panel (ECCP). See Fig. 1 .
2. Continue to depress OFF and WARM button until all segments and bulbs of the IPC, the Driver Information Center (DIC) and ECCP illuminate. See Fig. 2 . When all segments are lit, system has entered self-diagnostic mode. Release OFF and WARM button.
3. Illuminating the segments of the IPC, DIC and ECCP ensures all display segments are working properly. If all segments illuminate, proceed to DISPLAYING TROUBLE CODES in this article. Failure of any segment to illuminate may result in inaccurate test results. All inoperative segments of the display must be made to operate before proceeding with self-diagnostic procedures in this article.
4. Partial segment check is possible by depressing TEST button on IPC when vehicle is in PARK or NEUTRAL. Holding button depressed will light all vacuum fluorescent displays and all telltales on IPC in order to check for faulty bulbs or panels.

CAUTION:

Accessing self-diagnostics for 30 minutes or longer without running engine will cause battery to discharge, resulting in a possible no-start condition and faulty diagnostic readings. To ensure proper operation, attach battery charger to battery.

Fig. 1: Buick Riviera 1990 - Component Locations - Instrument Panel Cluster (Analog Gauges) & Electronic Climate Control Panel (ECCP)

Buick Riviera 1990 - EXIT SELF-DIAGNOSTICS

During self-diagnostic procedures, it is possible to exit service mode without erasing trouble codes. By depressing BI-LEV button on the ECC panel and turning ignition switch to OFF position.

Buick Riviera 1990 - DISPLAYING TROUBLE CODES

1. The Electronic Control Module (ECM), Body Control Module (BCM), and Supplemental Inflatable Restraint (SIR) trouble codes automatically display after system enters self-diagnostics. ECM trouble codes are displayed first, followed by the BCM trouble codes and then SIR trouble codes.
2. All trouble codes appear in an ascending (3 digit) numerical order. ECM codes are prefixed with the letter "E", BCM Codes prefixed with the letter "B", and SIR codes prefixed with the letter "R".
3. In addition, all trouble codes are followed by the letter "C" or "H". Letter "C" stands for current and indicates a trouble code related fault presently exists. Letter "H" stands for history and indicates the system failure was not present the last time the code was accessed.
4. For example: Code E016H is ECM trouble code number 016, set in response to a malfunction that occurred in the past (history). Code B410C is BCM trouble code number 410, set in response to a malfunction that is currently taking place.
5. If no ECM, BCM or SIR trouble codes are stored in memory, respectively, a NO E CODE, NO B CODE or NO R CODE message is displayed. Should the communication link between a component and the ECM or BCM fail, a NO B DATA, NO E DATA, or NO R DATA message will be displayed.
6. Trouble code display can be by-passed at any time by depressing FAN DOWN button on ECCP.

Buick Riviera 1990 BCM TROUBLE CODES

Code	Circuit Affected
B110	Outside Temperature Sensor Circuit
B111	A/C High Side Temperature Sensor
B112	A/C Low Side Temperature Sensor
B113	In-Car Temperature Sensor Circuit
B115	Sunload Sensor Circuit
B119	Twilight Photocell Circuit
B120	Twilight Delay Switch Pot Circuit
B121	Twilight Enable Switch Circuit
B122	Panel Dimming Switch
B123	Courtesy Lamp Switch Circuit
B124	Vehicle Speed Sensor Circuit
B132	Engine Oil Pressure Sensor Circuit
B140	Phone System Problem (CRT equipped)
B332	Loss of SIR Data to BCM
B334	Loss of ECM Data to BCM
B335	Loss of ECC Data or CRTM Data to BCM
B336	Loss of IPC Data to BCM
B337	Loss of Programmer Data to BCM
B33*	Multiple Intermittent Data Codes
B410	Charging System Problem
B411	Battery Voltage Too Low
B412	Battery Voltage Too High
B420	Relay Circuits
B440	HVAC-Air Mix Door Circuit
B446, 447 & 448	Low Refrigerant Pressure
B449	HVAC-High Side Temperature Too High
B450	HVAC-Coolant Temperature Too High
B482	Anti-Lock Pressure
B552	BCM Keep Alive Memory Error
B556	Odometer (EE) PROM Error
B660	Cruise Control Not in Drive
B663	Cruise - Vehicle Speed Too High Above Set Speed
B664	Cruise Acceleration Too High
B667	Set/Coast or Resume/Accel Switch Shorted
B671	Cruise - Servo Position Sensor Circuit
B672	Cruise - Vent Solenoid Circuit
B673	Cruise - Vacuum Solenoid Circuit

NOTE:

To repeat trouble code display sequence again, depress OFF button on ECCP.

Buick Riviera 1990 - CLEARING TROUBLE CODES

See CLEAR CODES under TEST TYPE SELECTION.

Buick Riviera 1990 - MANUAL OPERATION OF SERVICE MODE

NOTE:

Manual operation of service mode system is to be used with the TROUBLE CODE CHARTS section of this article. Prior to using flow charts, it will be necessary to become completely familiar with the procedures in MANUAL OPERATION OF SERVICE MODE.

Buick Riviera 1990 - SYSTEM SELECTION System Selection

1. After all trouble codes have been displayed, the SERVICE MODE system can be directed to perform specific system diagnostic tests. See DISPLAYING TROUBLE CODES in this article. Following the trouble code display, the first system available for testing will automatically be displayed. For example: ECM? may now be present on the display.
2. To select the desired system, (ECM, BCM, IPC, or SIR), advance and stop the DIC display as follows: Depressing the FAN DOWN button on the ECCP will cycle the system selection list. When the desired diagnostic system is displayed, depress FAN UP button on ECCP and the displayed system will be selected for testing.
3. Depressing BI-LEV button on ECCP will exit diagnostics and return to normal IPC and ECCP operation.

NOTE:

To cancel a system selection and activate a repeat of the system selection process, depress the OFF button on the ECCP.

Buick Riviera 1990 - TEST TYPE SELECTION Test Type Selection

1. After the diagnostic system has been selected for testing, 6 test types are now made available for selection. The menu choices are: CLEAR CODES?, DATA?, INPUTS?, OUTPUTS?, OVERRIDE? and SNAPSHOT?. The Season Odometer/DIC display may be showing any one of these 6 test type choices. The Trip Odometer will display selected value as seen by computer. See Fig. 2 -Fig. 7 .
2. To advance the display, depress FAN DOWN button on the ECCP.
3. When the desired test type is displayed, depress the FAN UP button on the ECCP.

NOTE:

To cancel a test type selection and activate a repeat of the test type selection process, depress the OFF button on ECC panel. To exit diagnostics without clearing codes, depress the BI-LEV button on ECCP.

The 6 test types are explained as follows:

Buick Riviera 1990 - CLEAR CODES

Selection of CLEAR CODES? will result in the message CODES CLEAR or CODES NOT CLEAR being displayed, indicating whether the codes were successfully cleared. This message appears for 3 seconds, indicating all stored trouble codes have been erased from that system's memory. After 3 seconds, the display will automatically return to the next test type available for testing. See Fig. 2 , Fig. 4 and Fig. 6 .

NOTE:

After trouble code has been cleared, a complete ignition cycle and possibly a test drive should be made, after which a recheck for the code should be made to ensure code did not reset.

Buick Riviera 1990 - DATA

Data test displays compare the malfunctioning system's present specifications with the specifications of a properly functioning system. Trip Odometer/DIC displays data values.

Buick Riviera 1990 - INPUTS

1. Input test displays the voltage level of that circuit tested as HI or LO. Input test display is shown in Trip Odometer/DIC panel.
2. HI or LO refers to input terminal voltage for the particular circuit. The display also indicates if an input reading has changed since the test was selected. This feature permits technician to activate or deactivate any listed device/circuit and then return to the display to see if voltage reading has changed.
3. If a voltage reading change occurs, an X will appear next to the HI/LO indicator; otherwise a "0" will remain displayed indicating no change occurred. The X will only appear once per selected input. The HI/LO indicator will continue to change as the input changes.

Buick Riviera 1990 - OUTPUTS

Output test displays the voltage level of selected device/circuit as HI or LO. After 3 seconds, this level will cycle between HI and LO voltage. Output test display is shown in Trip Odometer/DIC panel.

Buick Riviera 1990 - OVERRIDE

Override test is represented as a percentage of the tested functions' full range during its current operation. This percentage value is displayed in the ECCP temperature display area, The display will alternate between the override percentage value ("--") and the normal operation value. This alternating display is a reminder that the tested function IS NOT being overridden.

Pressing WARM and COOL buttons simultaneously on ECCP begins override of function. Alternating display will stop, and show override value.

Pressing WARM button increases value, pressing COOL button decreases value.

Normal program control is resumed in one of the following 3 ways:

• 1 - Selection of another override will cancel current override .
• 2 - Selection of another system (ECM, BCM, IPC or SIR) will cancel current override.
• 3 - Overriding the value beyond either extreme (0 or 90) will display "--" momentarily before resuming value. Releasing control button while "--" is displayed will resume normal program and display will start alternating.

Override test is unique in that while in override test, another test (i.e. DATA, INPUTS, or OUTPUTS) can be selected and be active at the same time with override test. After selecting override test, press the OFF button, to allow selection of another test type. ECCP will continue to display selected override. By pressing OFF and WARM or COOL buttons at same time, it is possible to monitor effect of override on different parameter.

To exit diagnostics without clearing codes, depress the BI-LEV button on ECCP.

Buick Riviera 1990 - SNAPSHOT

Snapshot is a test type that will record all BCM or ECM data and inputs at one instant for review at a later time. Snapshot also permits a technician triggered recording of specific current BCM/ECM data and input parameters for review at a later time. BCM and ECM have slightly different types of snapshot.

NOTE:

Proceed to SNAPSHOT after selecting snapshot test type.

Buick Riviera 1990 - EXPLANATION OF SPECIFIC TEST SELECTION

1. Following test type selection, the first of many specific tests will be made available for selection. The 4 characters of this display represent a test code. The first 2 characters of the test code are alphabetic letters which identify both the system and test type already selected. Study the following examples:
   • If the BCM system and DATA test type were selected, BD will be the first 2 characters of the display. BD stands for BCM DATA. The last 2 characters numerically identify the specific test selection. For example: BD51 designates BCM DATA, test 51.
   • If the ECM system and Data test type were selected, ED will be the first 2 characters of the display. ED stands for ECM DATA. The numerals following these 2 characters will represent the particular specific test selection.
   • When BI appears as the first 2 characters of the test code, this signifies the BCM system and INPUT test type were selected. The last 2 characters numerically identify the specific test selection. For example: BI51 designates BCM INPUT, test 51.

Buick Riviera 1990 - MAKING SPECIFIC TEST SELECTION

Scrolling to a lower specific test number is done by depressing the FAN DOWN button. Scrolling to a higher specific test number is done by depressing the FAN UP button. The system will automatically display the values for whatever specific test number is displayed.

NOTE:

To cancel a specific test type selection and activate a repeat of the specific test type selection process, depress the OFF button on ECCP.

Buick Riviera 1990 - BCM SNAPSHOT

NOTE:

If directed here from TEST TYPE SELECTION under MANUAL OPERATION OF SELF-DIAGNOSTICS in this article, go to step 2).

1. Snapshot allows the recall of system operating specifications present at the exact time a BCM malfunction code was set. Up to 3 snapshots may be recalled. In addition, one snapshot may be triggered on demand by depressing FAN UP button when DO B SNAP is displayed. See Fig. 5 .

   To enter snapshot, complete the following:

   • Enter self-diagnostics. See ENTERING SELF-DIAGNOSTICS under SELF-DIAGNOSTICS in this article.
   • Display trouble codes stored in memory. See DISPLAYING TROUBLE CODES under SELF-DIAGNOSTICS in this article.
   • Select BCM system for testing. See SYSTEM SELECTION under MANUAL OPERATION OF SELF-DIAGNOSTICS in this article.
   • Select SNAPSHOT test type. See TEST TYPE SELECTION under MANUAL OPERATION OF SELF-DIAGNOSTICS in this article.

   NOTE:

   To cancel snapshot test type selection and activate a repeat of the specific test type selection process, depress the OFF button on ECCP.

2. Immediately following the selection of SNAPSHOT?, the system will display BXXX. B stands for BCM. XXX is used here to represent the 3 digit trouble code stored in BCM snapshot memory.
3. With BXXX displayed, depressing the LO button on the ECC panel will permit scrolling through the list of BCM diagnostic codes for which the BCM has stored a snapshot. See BCM TROUBLE CODES under SELF-DIAGNOSTICS in this article for list of BCM trouble codes which may be present in snapshot.

   NOTE:

   A trouble code displayed during the trouble code display cycle may NOT be present as a snapshot trouble code. If this is the case, exit SNAPSHOT by depressing the OFF button on the ECCP. This will return the display to the next available system selection.

4. After display of the last BCM trouble code for which a snapshot does exist, pressing the FAN DOWN button on the ECCP will result in the DO B SNAP display.
5. Responding to this display by depressing the FAN DOWN button on the ECCP will return the display to the first BXXX SNAP? display. Responding to the DO B SNAP display by depressing the HI button with SNAP DATA? or SNAP INPUTS? displayed, will select that test type for display.
6. At this point the display is controlled as it would be for non-snapshot data and inputs display, however, all values and status information represents memorized vehicle conditions. See EXPLANATION OF SPECIFIC TEST SELECTION and MAKING SPECIFIC TEST SELECTION under MANUAL OPERATION OF SELF-DIAGNOSTICS in this article.
7. Depressing the HI button again with DO B SNAP? displayed will change DIC to display the SNAP DONE message to indicate new information has been stored in memory.

Fig. 2: Buick Riviera 1990 - Component Locations - Diagnostic ECM Flow Chart (1 of 6)

Fig. 3: Buick Riviera 1990 - Component Locations - Diagnostic ECM Flow Chart (2 of 6)

Fig. 4: Buick Riviera 1990 - Component Locations - Diagnostic ECM Flow Chart (3 of 6)

Fig. 5: Buick Riviera 1990 - Component Locations - Diagnostic ECM Flow Chart (4 of 6)

Fig. 6: Buick Riviera 1990 - Component Locations - Diagnostic ECM Flow Chart (5 of 6)

Fig. 7: Buick Riviera 1990 - Component Locations - Diagnostic ECM Flow Chart (6 of 6)

Buick Riviera 1990 - STATUS LIGHT INDICATORS DESCRIPTION

During self-diagnostics, the status light display on ECC Panel is used to indicate switchable parameter status. Each different mode of operation is indicated by it's status light being turned ON or OFF. Status light indicators are relative to system level being tested (BCM or ECM). See Fig. 2 and Fig. 4 .

Following are brief summaries of each systems status light indicators, starting with the ECM status light indicators:

• HIGH indicator light will be ON when ECM is in closed loop fuel control. Light comes ON only after coolant and O2 sensors reach operating temperature.
• MED indicator light only indicates whether operation is enabled (ON) or disabled (OFF) by ECM. Actual working operation depends on TCC system being in working order.
• LOW indicator light stays ON when oxygen sensor signals rich exhaust condition to ECM. Light will flash ON and OFF during warm engine, steady throttle, and proper fuel mix condition.
• LOWER ARROW indicator light will be ON when ECM is directing one of the 3 EGR solenoids to be ON. Light will be OFF if no EGR solenoids are ON as during idle condition.
• OFF indicator light will be ON when ECM senses 4th gear pressure switch open. Light should only be on in 4th gear.
• Left-side AUTO indicator light will be ON when ECM senses 3th gear pressure switch open. Light should only be on in 3rd or 4th gear.
• "?C" indicator light will be ON when ECM senses 2nd gear pressure switch open. Light should only be on in 2nd, 3rd or 4th gear.
• A/C Compressor Command LOWER ARROW indicator light will be ON only when ECM allows A/C clutch engagement through A/C relay. Light will also be ON if BCM requests ECM to turn clutch ON during test sequence. Light should be OFF if ECM commands disengagement.

Following are brief summaries of BCM system status light indicators:

• LOWER ARROW indicator light will be ON if BCM senses low refrigerant pressure switch is open. Light will remain OFF if A/C system is fully charged and operational. (However, light will come ON when outside vehicle ambient temperature is below -5?F (-21?C), this is due to temperature-pressure relationship of R-12 refrigerant.)
• OFF indicator light will be ON when BCM commands air recirculation.
• MED indicator light will be ON when BCM commands airflow out A/C vents. Light should also be ON in A/C and BI-LEV modes.
• LOW indicator light will be ON when BCM commands airflow out defroster outlets. Light should also be ON in defrost and A/C modes.
• HIGH indicator light will be ON when BCM commands airflow out floor outlets. Light should be ON in heater mode.
• Left-side AUTO indicator light will be ON when BCM requests ECM to engage A/C compressor clutch.

Buick Riviera 1990 - DATA DISPLAY CODES

Brief summary of each DATA parameter is as follows:

Buick Riviera 1990 - BCM DATA PARAMETERS:

• BD20 Commanded blower voltage in volts from 0 to 18.0 volts.
• BD21 Coolant temperature displayed in degrees Celsius (?C) from -40 to 151. This value is sent from ECM to BCM. If circuit malfunctions, ECM will send BCM a FAILSOFT value for display.
• BD22 Commanded air mix door position displayed in percent. Value close to 0% represents cold air mix and value close to 100% represents warm air mix.
• BD23 Actual air mix door position displayed in percent. This value should follow commanded air mix door position (BD22) except when door is commanded beyond its mechanical limits of travel.
• BD24 Air delivery mode displayed as number from 0 to 10. Each number is code which represents following air delivery modes: 0 - Auto-Recirc/MAX A/C outlets 1 - Auto-A/C outlets 2 - Auto-Bi-Level outlets 3 - Auto-Heater-Def outlets 4 - Auto-Heater outlets 5 - OFF 6 - Normal purge 7 - Cold (DEF) purge 8 - Forced/Def outlets 9 - Forced (Fan) Heater outlets 10 - Forced (Fan) Bi-Level outlets 11 - A/C Purge
• BD25 In-car temperature is displayed in degrees Celsius (?C) from -40 to 102.
• BD26 Actual outside temperature displayed in degrees Celsius (?C) from -40 to 58. This value represents actual sensor temperature and is not buffered by software.
• BD27 A/C High side temperature (condenser output) displayed in degrees Celsius (?C) from -40 to 215.
• BD28 A/C Low side temperature (evaporator input) displayed in degrees Celsius (?C) from -40 to 93.
• BD32 Sunload temperature sensor displayed in degrees Celsius (?C) from -40 to 102.
• BD40 Actual fuel level read in gallons between 0 to 25.5. Value represents actual sensor position and is not restricted by features used to eliminate fuel slosh affects on IPC display value.
• BD42 Dimming pot displayed in percent. Value close to 0% represents maximum dimming and value close to 100% represents maximum brightness.
• BD43 Twilight delay pot displayed in percent. Value close to 0% represents minimum delay time and value close to 100% represents maximum delay time.
• BD44 Twilight Photocell displayed in percent. Value close to 0% represents daylight and value close to 100% represents darkness.
• BD50 Battery voltage read in volts between 0 and 25.5.
• BD51 Generator field displayed in percent. Value close to 0% represents minimum regulator on time and value close to 100% represents maximum regulator on time.
• BD60 Vehicle speed displayed in miles per hour from 0 to 159.
• BD61 Engine speed displayed in RPM from 0 to 6375.
• BD70 Cruise servo position displayed in percent from 0 to 100%. Value close to 0% represents at rest position and value close to 100% represents wide open throttle.
• BD71 Oil pressure sensor displayed in PSI from 0 to 80.
• BD98 Ignition cycle value is the number of times that the BCM has been turned OFF since BCM trouble code was last detected. After 99 ignition cycles, (where each OFF, CRANK, OFF cycle counts as 2), without any malfunction being detected, all BCM codes are cleared.
• BD99 BCM PROM I.D. displayed as number, up to four digits long, which can be used to verify that proper PROM was installed in BCM.

Buick Riviera 1990 - INPUT DISPLAY CODES

Brief summary of each systems INPUT parameters is as follows.

Buick Riviera 1990 - BCM INPUT PARAMETERS:

• BI01 Panel lamp switch display is LO when panel lamp switch is in off position.
• BI02 Park lamp switch display is LO when parklamp switch is in off position.
• BI03 Driver door ajar switch display is LO when drivers front door is ajar.
• BI04 Passenger door ajar switch display is LO when passengers door is open.
• BI05 Door jamb switch display is LO when any door is open.
• BI06 Door handle switch display is momentarily LO when either outside door handle button is depressed.
• BI08 Low refrigerant pressure switch display is LO when system is low on refrigerant.
• BI09 Washer fluid level switch display is LO when vehicle is low on washer fluid.
• BI16 Key in ignition display is LO "only" when key is in LOCK position. (With ignition ON, display will always read HI.)
• BI18 Brake pressure signal is LO when brake controller detects pressure problem.
• BI21 Low brake fluid display is LO when brake fluid is low.
• BI22 Park brake switch display is LO when parking brake is applied.
• BI24 Fog lamp switch display is LO whenever switch is pressed.
• BI25 Seat belt switch display is HI when drivers seatbelt is fastened.
• BI51 Generator feedback display is LO when there is generator problem or engine not running.
• BI71 Cruise control brake switch display is HI when cruise ON/OFF switch is ON and brake pedal is not depressed .
• BI75 Cruise control on/off switch display is HI when cruise ON/OFF switch is ON and set/coast switch is depressed.
• BI76 Cruise control set/coast switch display is HI when cruise ON/OFF switch is ON and set/coast switch is pushed.
• BI77 Cruise control resume/accel switch display is HI when cruise ON/OFF switch is ON and resume/accel switch is pushed.
• BI78 Headlamps display is HI whenever headlamp switch is ON.
• BI79 High beam switch display is LO as long as lever is pulled in.
• BI82 Twilight enable switch display is LO whenever twilight sentinel headlamp switch is ON (Riviera Only).
• BI83 Fog lamp switch display is HI whenever fog lamps switch is ON (Reatta Only).
• BI88 Low oil level switch display will be HI when engine oil level is low.

Buick Riviera 1990 - IPC INPUT PARAMETERS:

• II10 Speedo select switch display is HI as long as switch on IPC is depressed.
• II11 Fuel gauge switch display is HI as long as switch on IPC is depressed.
• II12 Trip reset switch display is HI as long as switch on IPC is depressed.
• II13 English/Metric switch display is HI as long as switch on IPC is depressed.

Buick Riviera 1990 - OUTPUT DISPLAY CODES

Brief summary of each systems OUTPUT parameters is as follows.

Buick Riviera 1990 - BCM OUTPUT PARAMETERS:

• BO00 No outputs display will not show HI or LO. This is normal resting code where no outputs will be cycled.
• BO01 Cruise control vent solenoid display is HI when vent solenoid is ON (energized). Cruise ON/OFF switch must be ON for output to cycle.
• BO02 Cruise control vacuum solenoid display is HI when vacuum solenoid is ON (energized). Cruise ON/OFF switch must be ON for output to cycle.
• BO03 Retained accessory power (RAP) relays display is LO when relays are ON (energized).
• BO04 Courtesy lamps relay display is LO when relay is ON (energized).
• BO06 Hi/Lo beam relay display is LO when relay is ON (energized) and hi beams ON.
• BO10 CHIME 1 display is LO when fast chime is ON (sounding).
• BO11 CHIME 2 display is LO when slow chime is ON (sounding).
• BO12 Fog lamp Daytime Running Lights (DRL) display is LO when foglight relay is ON (Reatta Only).
• BO13 Twilight display (Riviera) is LO when relay is ON (energized). (Reatta) Park lamps are on when relay is LO.
• BO14 DRL (Daytime Running Lights) - Display is LO when relays are ON (energized) lights ON (Riviera Only)

Buick Riviera 1990 - OVERRIDE DISPLAY CODES

Brief summary of each OVERRIDE parameter is as follows.

Buick Riviera 1990 - BCM OVERRIDE PARAMETERS:

• BS00 No Overrides display will not show any value in display area on ECCP, as no overrides are active at this point. This is normal resting code where no overrides will be controlled. This code can be used to stop override control without having to go back to system selections.
• BS01 Program Number will automatically change as heating and A/C operating conditions change. Program number can be manually overridden using UP arrow and DOWN arrow buttons. UP arrow button will increase number at controlled rate until MAX HEAT mode value of "99" is reached. DOWN arrow button will decrease number at controlled rate until MAX A/C mode value of "0" is reached. Manual override will continue until override code is canceled. This manual override control allows technician to alter and observe reactions of system change on other BCM data parameters.
• BS02 Vacuum Fluorescent (VF) Dimming Number will automatically change as dimming switch position is moved (only if exterior lights are ON). Using override controls, UP arrow and DOWN arrow buttons, automatic dimming can be manually controlled. Use "99" to represent maximum brightness of VF displays and "0" to represent maximum dimming of VF displays, (exterior lights need not be on when overriding dimming).
• BS03 - Bulb Dimming As dimming switch position is moved, incandescent dimming number will automatically change (only if exterior lights ON). Using override controls, UP arrow and DOWN arrow buttons, automatic dimming can be manually controlled. Using "99" to represent maximum brightness and "0" to represent maximum dimming of incandescent lighting, (exterior lights need not be on when overriding dimming).
• BS05 - C/C Servo With engine OFF, ignition ON. Cruise control switch must be ON to override automatic calculations for cruise control. Using "99" to represent maximum cruise position (WOT) and "0" to represent minimum cruise position (closed throttle). Manual override will continue until override code is canceled. This manual override control allows technician to alter cruise control position and observe reactions of data value for cruise servo position (BD70). The two parameters should agree within 3% except when servo is commanded beyond its mechanical travel limits. Remember that there is ONLY enough vacuum in storage tank to operate servo ONCE.
• BS07 - Option Content #1 This override allows the ability to change contents of which options the vehicle's BCM has stored in its EEPROM. This option content is displayed in trip odometer as a number from 0 to 255. Each number is a code which represents option content. BCM uses this value to determine how to operate the displays and electronic controls. Incorrect option values cause many different problems.

  To determine proper option value, add up following options that vehicle is equipped with: U.S. vehicle (not Canadian or export model) - 128; Reatta body style - 16; Export displays (export car, option code NM8) - 32; Twilight sentinel - 2.

  Take total of actual options vehicles has from above list and compare it with Option 1 value on ECCP display. If the two are different, correct Option 1 value using following procedure. To change option content number press UP arrow or DOWN arrow button for override control until desired number appears, (corresponding to total of actual options vehicle does have). Next, press and hold HEATER and DEFROST buttons simultaneously for 3 seconds. This will reprogram BCM EEPROM to number of options displayed on the IPC odometer.

• BS08 - Option Content #2 This override allows the ability to change contents of which options the vehicle's BCM has stored in its EEPROM. This option content is displayed in trip odometer as number from 0 to 255. Each number is a code which represents option content. BCM uses this value to determine how to operate the displays and electronic controls. Incorrect option values cause many different problems.

  To determine proper option value add up following options that vehicle is equipped with: Oil level sensor (All vehicles) - 4; Anti-lock brakes (option code JL9) - 32; Washer fluid level sensor (All vehicles) - 128; Universal Theft Deterrent - 64 (This is NOT Pass-Key Theft Deterrent System that comes standard with vehicle).

  Take total of actual options vehicle has from above list and compare it with Option 2 value on ECCP display. If the two are different, correct Option 2 value using following procedure: To change option content number press UP arrow or DOWN arrow button for override control until desired number appears, (number corresponding to total of actual options vehicle does have). Next, press and hold both HEATER and DEFROST buttons for 3 seconds. This will reprogram BCM EEPROM to number of options displayed on the IPC odometer.

Buick Riviera 1990 - DIAGNOSTIC CHARTS SELF-DIAGNOSTIC SYSTEM CHECK

The self-diagnostic system check is an organized approach for identifying a problem caused by on-car computer controlled electronics. Understanding this chart and using it correctly will reduce diagnosis time, prevent unnecessary replacement of parts, and reduce comebacks. To review the basic information on how to use the computer self-diagnostics, go to beginning of this section.

Buick Riviera 1990 - Always Start Electrical Or Electronic Diagnosis Here

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) Service Engine Soon telltale light at key ON confirms battery, ignition, and ground integrity to ECM and also verifies Ignition 1 power feed to IPC.

Test Number 2) IPC odometer is primary display device for diagnostics and must be functional in order to use self-diagnostics system.

Test Number 3) ECCP serves as access for onboard diagnosis and must be functional in order to use self-diagnostic system. A display other than standard temperature indicates fault that must be corrected before diagnostics can be entered.

Test Number 4) After entering diagnostics, record all displayed trouble codes and note those that display CURRENT and HISTORY code. Codes displayed can be diagnosed using the procedures outlined in referenced articles, but those codes displayed as HISTORY are not presently failing and may require visual inspection of circuitry to isolate.

Test Number 5) Failure of SES light to go out in the expected time period indicates ECM problem.

Fig. 8: Buick Riviera 1990 - Component Locations - Self-Diagnostic System Check Flow Chart

Buick Riviera 1990 - CHART A-1, NO SERVICE ENGINE SOON LIGHT

The SERVICE ENGINE SOON light is attached to the IPC. It is powered by CPS circuit No. 812 and ECM completes the ground to turn the light on. The light will be ON while engine is not running. With the engine running, a steady light indicates an ECM code is set. When the engine is running and diagnostics are entered, a flashing light indicates the operating service mode of the ECM. The system monitor button will not affect the SERVICE ENGINE SOON light.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) This step splits the circuit into 2 sections. A SES light on after grounding terminal "D", indicates the open is on ECM side of circuit split. With the SES light off, indicates the open is on IPC side of circuit.

Test Number 2) If test light does not light when connected between IPC terminal B12 and ground, feed circuit for the SES bulb is open.

Test Number 3) If test light did not illuminate when connected between ECM terminal BA6 and ground, ECM will not be powered up. This is a result of an open or short to ground (blown fuse) in circuit No. 439.

Test Number 4) This test checks if open is in IPC or circuit No. 419, since IPC terminal B12 is battery voltage. With test light connected between terminals B12 and L5, test light should illuminate, indicating circuit No. 419 is complete through ALDL terminal "D" which has been jumpered to ground.

Test Number 5) This test checks if open is in ECM or circuit No. 419. If test light illuminates when ECM terminal YC11 is grounded, fault is in a poor terminal contact at YC11 or a faulty ECM.

Buick Riviera 1990 - Diagnostic Aids

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

• Poor Connection. Check at ECM pin YC11 or IPC connector. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal to wire connections.
• Damaged Harness. Inspect harness for damage. If harness appears okay, observe related connectors and wiring harness. A flickering light would indicate the intermittent fault location.

Fig. 9: Buick Riviera 1990 - Component Locations - Chart A-1 Circuit Diagram

Fig. 10: Buick Riviera 1990 - Component Locations - Chart A-1 Flow Chart

Buick Riviera 1990 - CHART A-2: "SERVICE ENGINE SOON" LIGHT WON'T GO OUT OR FLASH

The SERVICE ENGINE SOON light is attached to the IPC. It is powered by CPS circuit No. 812 and ECM completes the ground to turn the light on. The light will be ON while engine is not running. With the engine running, a steady light indicates an ECM code is set. When the engine is running and diagnostics are entered, a flashing light indicates the operating service mode of the ECM. The system monitor button will not affect the SERVICE ENGINE SOON light.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) This step verifies that SES light remains ON with engine running and no ECM codes displayed.

Test Number 2) Unplugging ECM Yellow harness connector determines if short to ground exists in the ECM or in the circuit. If SES light remains on, fault is not in ECM.

Test Number 3) This step removes the IPC from circuit to distinguish between a grounded IPC or a grounded circuit No. 419. If test light is illuminated when connected between IPC harness terminals B12 and LT5, circuit No. 419 is shorted to ground.

Buick Riviera 1990 - Diagnostic Aids

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

• Poor Connection. Check at ECM pin YC11 or IPC connector. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal to wire connections.
• Damaged Harness. Inspect harness for damage. If harness appears okay, observe related connectors and wiring harness. A flickering light would indicate intermittent fault location.

Fig. 11: Buick Riviera 1990 - Component Locations - Chart A-2 Circuit Diagram

Fig. 12: Buick Riviera 1990 - Component Locations - Chart A-2 Flow Chart

Buick Riviera 1990 - CHART A: BLANK ODOMETER DISPLAY

Loss of IPC display and messages can result from the following:

• Loss of 12 volt power to IPC (circuit No. 812).
• Loss of ground to IPC (circuit No. 803).
• Internal fault in CPS or IPC.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) This test checks if BCM is awake and if CPS is partially functioning.

Test Number 2) Since BCM controls courtesy lights, CPS should be supplying 12 volts through circuit No. 812. Since CPS is functioning, check IPC power and grounds.

Test Number 3) Fault is either internally in IPC or in terminal contacts, since power, Ignition 3 and ground circuits are functioning.

Test Number 4) CPS is supplying 12 volts to BCM, but not to IPC. CPS has internal fault.

Test Number 5) CPS is not delivering 12 volt output. Check power supply and ground to CPS.

Test Number 6) This step checks for short to ground in all No. 812 circuits.

Test Number 7) This step checks for short to ground to be inside component or in circuit itself.

Fig. 13: Buick Riviera 1990 - Component Locations - Chart A: Circuit Diagram

Fig. 14: Buick Riviera 1990 - Component Locations - Chart A: Flow Chart Blank Odometer Display

Buick Riviera 1990 - CHART B: ODOMETER DISPLAYS ERROR (LOSS OF SERIAL DATA)

IPC indicates loss of serial data communication by displaying ERROR in odometer and illuminating ELECTRICAL PROBLEM telltale light.

Loss of serial data communications can occur for the following reasons:

• Short to ground somewhere in circuit No. 800.
• Short to voltage somewhere in circuit No. 800.
• Two opens in circuit No. 800.
• Internal fault in BCM, CPS or IPC.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) This steps checks if BCM is awake and functioning. If it is not, use chart B-1 to isolate fault.

Test Number 2) This step checks if ECC head has lost data communication along with IPC.

Test Number 3) Code B556 indicates IPC EEPROM error. Odometer will display ERROR, diagnostics will be accessible.

Test Number 4) Since IPC lost data communications, creating an open in data line at ALDL connector should remove data communications from ECC head. If not, IPC is receiving data but is unable to communicate due to poor connection or internal problem.

Test Number 5) This test indicates data line shorted to ground.

Test Number 6) This test indicates data line functioning properly, but with multiple opens isolating IPC and ECCP from BCM.

Test Number 7) This test indicates data line shorted to voltage.

Fig. 15: Buick Riviera 1990 - Component Locations - Chart B: Circuit Diagram

Fig. 16: Buick Riviera 1990 - Component Locations - Chart B: Flow Chart Blank Odometer Displays Error

Buick Riviera 1990 - CHART B-1, CPS/BCM WAKE-UP CHECK

CPS provides filtered 12 volts, 7 volts, and ground for most of major computers in system. BCM is continuously supplied 12 volts from CPS. When "wake-up" signal (such as opening door or turning ignition ON) is received at BCM, 12 volt signal is sent (on circuit No. 555) from BCM to CPS to turn ON 7 volt power supply. The 7 volt powers various computers that control serial data communications. The BCM needs constant 12 volts from CPS, and good ground to function properly. BCM must supply wake-up signal to activate 7 volt supply in CPS.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) This step checks for wake-up signal back to CPS. If voltage is HI, wake-up signal is occurring and fault is in 7 volt circuit. LO voltage indicates that wake-up is NOT occurring.

Test Number 2) This step checks for source of short by testing all 7 volt circuits and related components for short to ground. If 7 volt circuits are okay, then fault is internal in IPC or BCM.

Test Number 3) This step checks 12 volt power circuit from CPS to BCM.

Test Number 4) This step checks BCM for 12 volts into itself and for wake-up voltage out coming out of BCM.

Test Number 5) This step checks BCM for crank signal. If 12 volts are on pin 3C11 (crank circuit), BCM goes down and brings CPS down with it.

Fig. 17: Buick Riviera 1990 - Component Locations - Chart B-1: Circuit Diagram

Fig. 18: Buick Riviera 1990 - Component Locations - Chart B-1: Flow Chart CPS/BCM Wake-Up Check

Buick Riviera 1990 - CHART C: ECC DISPLAY PROBLEMS (LOSS OF ECC COMMUNICATIONS)

When ECC communications are lost service diagnostics usually cannot be entered, but a quick scan of panel will usually help isolate source of fault. ECC panel is powered by ignition. If power source is lost the panel will usually display segment check. Loss of serial data will result in 3 dashes being shown on panel VF display ("---"). This indicates power and ground are okay. If the panel displays normal outside or interior set temperature, power, ground and serial communications are being received thus panel replacement is indicated.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) This step checks for power and ground to panel. Voltage should be HI for both power to ground checks.

Test Number 2) This step checks for serial data voltage. Normal voltage should be more than one volt and varying. Steady voltage indicates second open exists, or ALDL cover is off.

Fig. 19: Buick Riviera 1990 - Component Locations - Chart C: Circuit Diagram

Fig. 20: Buick Riviera 1990 - Component Locations - Chart C: Flow Chart ECC Display Problems

Buick Riviera 1990 - CHART D-1, GROUNDED SERIAL DATA CIRCUIT

With grounded serial data circuit BCM will not be able to communicate with any other devices in system. Voltage measured anywhere in circuit will zero. IPC will display ELECTRICAL PROBLEM, ECCP will display dashes ("---").

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) This step splits the system in half to help isolate source of grounded serial data line. If taking IPC out of the system allows both halves of serial data line to rise more than one volt, source of short has been located.

Test Number 2) The remaining steps follow same pattern in that components are removed from serial data line until normal voltage range is again measured. When section of circuit is isolated, a simple check of wire for short to ground will differentiate between grounded wire or ground in a device remote.

Fig. 21: Buick Riviera 1990 - Component Locations - Chart D-1: Circuit Diagram

Fig. 22: Buick Riviera 1990 - Component Locations - Chart D-1: Flow Chart Grounded Serial Data Circuit

Buick Riviera 1990 - CHART D-2: SERIAL DATA CIRCUIT SHORTED TO VOLTAGE

With a shorted serial data circuit BCM will not be able to communicate with other devices in system. Voltage measured any where in circuit will be more than 5 volts. IPC display showing only ELECTRICAL PROBLEM.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) This step splits system in half to help isolate the source of short in the serial data line. If taking ECM out of system allows both halves of serial data line to fall below 5 volts, source of short was in IPC.

Test Number 2) The remaining steps follow the same pattern in that components are removed from serial data line until normal voltage range is again measured.

Fig. 23: Buick Riviera 1990 - Component Locations - Chart D-2: Circuit Diagram

Fig. 24: Buick Riviera 1990 - Component Locations - Chart D-2: Flow Chart Serial Data Circuit (Shorted To Voltage)

Buick Riviera 1990 - BCM TROUBLE CODE CHARTS CODE B110: OUTSIDE TEMP SENSOR CIRCUIT

The outside air temperature sensor is a thermistor located behind grill that controls signal voltage to BCM. The BCM applies and monitors voltage on circuit No. 735 to sensor. When sensor is cold, its resistance is high, therefore BCM will see a high monitored voltage. As sensor warms, its resistance becomes less and signal voltage is pulled low through sensor ground, circuit No. 736. This signal voltage will vary between 5 volts (open circuit) and zero volts (shorted circuit).

Code B110 will set if ignition is on and signal voltage indicates less than -31?F (-35?C), which is open circuit voltage or greater than 137?F (58?C), which is shorted circuit voltage. During time failure is present, a substitute temperature reading will be used to allow continued operation of the climate control system, and continuous compressor at idle will be disabled. The outside air temperature reading BD26 display will indicate the actual sensor reading.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks to see if open circuit reading is due to circuit or sensor. If open circuit reading changes to a shorted circuit reading after jumping sensor terminals, BCM and wiring are okay.

Test Number 2) By applying a ground to various points in the circuits, an open can be isolated by observing whether parameter display can be changed from an open reading to shorted reading.

Test Number 3) Checks to see if shorted circuit reading is due to circuit or sensor. If shorted circuit reading changes to an open circuit reading after disconnecting sensor, BCM and wiring are okay.

Buick Riviera 1990 - Note on Intermittents

If ambient temperature drops to less than about -31?F (-35?C), this code should be ignored. If B110 is set with any of the following codes: B119, B120, B122, B132 or B440, the most likely cause is an intermittent open circuit No. 736.

If an intermittent Code B110 is being set, check B110 snap data value for outside temperature BD26. If BD26 value is less than -29?F (-34?C), code was caused by an open circuit No. 735, circuit No. 736 or outside temperature sensor. If BD26 value is over 135?F (57?C), code was caused by a short to ground on circuit No. 735 or a shorted outside temperature sensor. Manipulate related wiring while observing BCM display BD26. If failure is induced, reading will jump from its normal value to a reading outside the range of -31?F (-35?C) to 137?F (58?C).

If value indicated by BD26 display is not reasonably close to actual temperature of air at sensor, check for poor terminal contact or replace sensor.

Fig. 25: Buick Riviera 1990 - Component Locations - Code B110: Circuit Diagram

Fig. 26: Buick Riviera 1990 - Component Locations - Code B110: Flow Chart Outside Temp Sensor Circuit

Buick Riviera 1990 - CODE B111: A/C HIGH SIDE TEMP SENSOR CIRCUIT

The A/C high side temperature sensor is a thermistor that controls signal voltage to BCM. The BCM applies and monitors voltage on circuit No. 732 to sensor. When sensor is cold, its resistance is high, therefore, BCM will see a high monitored voltage. As sensor warms, resistance becomes less and signal voltage is pulled low through sensor ground, circuit No. 736. This monitored voltage will vary between 5 volts (open circuit) and zero volts (shorted circuit).

Code B111 will set if ignition is on, outside temperature sensor has not failed and reads greater than 32?F (0?C), and signal voltage indicates less than -24?F (-31?C), which is open circuit voltage or greater than 408?F (209?C), which is shorted circuit voltage. During time failure is present, a substitute temperature reading will be used to allow continued operation of climate control system. The A/C high side temperature reading BD27 display will indicate actual sensor reading.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks to see if open circuit reading is due to circuit or sensor. If open circuit reading changes to a shorted circuit reading after jumping sensor terminal, BCM and wiring are okay.

Test Number 2) By applying a ground to various points in circuits, an open can be isolated by observing whether parameter display can be changed from open reading to shorted reading.

Test Number 3) Checks to see if shorted circuit reading is due to circuit or sensor. If shorted circuit reading changes to an open circuit reading after disconnecting sensor, BCM and wiring are okay.

Buick Riviera 1990 - Note on Intermittents

If Code B111 is set with Code B112, check for an intermittent open in circuit No. 736. If an intermittent Code B111 is being set, check Code B111 snap data value for high side temperature, BD27 display. If BD27 display value is less than -27?F (-33?C), code was caused by an open in circuit No. 732, circuit No. 736 or high side temperature sensor. If BD27 display is greater than 408?F (209?C), code resulted from a short to ground on circuit No. 732 or a shorted high side temperature sensor. Manipulate related wiring while observing BD27 display. If failure is induced, reading will jump from its normal value to a reading outside the range of -24?F (-33?C) to 408?F (209?C).

If value displayed by BD27 display is not reasonably close to corresponding gauge pressure reading, check for poor terminal contact or replace sensor.

Fig. 27: Buick Riviera 1990 - Component Locations - Code B111: Circuit Diagram

Fig. 28: Buick Riviera 1990 - Component Locations - Code B111: Flow Chart A/C High Side Temp Sensor Circuit

Buick Riviera 1990 - CODE B112: A/C LOW SIDE TEMP SENSOR CIRCUIT

The A/C low side temperature sensor is a thermistor that controls signal voltage to BCM. The BCM applies and monitors voltage on circuit No. 731 to sensor. When sensor is cold, its resistance is high, therefore, BCM will see a high monitored voltage. As sensor warms, its resistance becomes less and signal voltage is pulled low through sensor ground, circuit No. 736. This monitored voltage will vary between 5 volts (open circuit) and zero volts (shorted circuit).

Code B112 will set if ignition is on, outside temperature sensor has not failed and reads greater than 32?F (0?C), and signal voltage indicates less than -29?F (-34?C), which is open circuit voltage or greater than 209?F (85?C), which is shorted circuit voltage. During time failure is present, a substitute temperature reading (same value as outside air temperature) will be used to allow continued operation of climate control system and compressor clutch will be disabled. The A/C low side temperature reading BD28 display will display actual sensor reading.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks to see if open circuit reading is due to circuit or sensor. If open circuit reading changes to a shorted circuit reading after jumping sensor terminals, BCM and wiring are okay.

Test Number 2) By applying a ground to various points in circuits, an open can be isolated by observing whether parameter display can be changed from open reading to shorted reading.

Test Number 3) Checks to see if shorted circuit reading is due to circuit or sensor. If shorted circuit reading changes to an open circuit reading after disconnecting sensor, BCM and wiring are okay.

Buick Riviera 1990 - Note on Intermittents

If an intermittent Code B112 is being set, manipulate related wiring while observing BD28 display. If failure is induced, reading will jump from its normal value to a reading outside the range of -34?F (-29?C) to 209?F (85?C).

If value indicated by BD28 display is not reasonably close to corresponding gauge pressure reading, check for poor terminal contact or replace sensor.

Fig. 29: Buick Riviera 1990 - Component Locations - Code B112: Circuit Diagram

Fig. 30: Buick Riviera 1990 - Component Locations - Code B111: Flow Chart A/C Low Side Temp Sensor Circuit

Buick Riviera 1990 - CODE B113: IN-CAR TEMP SENSOR CIRCUIT

The in-car temperature sensor is a thermistor that controls signal voltage to BCM. The BCM applies and monitors voltage on circuit No. 734 to sensor. When sensor is cold, its resistance is high, therefore, BCM will see a high monitored voltage. As sensor warms, its resistance becomes less and monitored voltage is pulled low through sensor ground, circuit No. 736. This signal voltage will vary between 5 volts (open circuit) and zero volts (shorted circuit).

Code B113 will set if ignition is on, outside temperature sensor has not failed and reads greater than 32?F (0?C), and signal voltage indicates less than -29?F (-34?C), which is open circuit voltage or greater than 209?F (85?C), which is shorted circuit voltage. During time failure is present, a substitute temperature reading will be used to allow continued operation of climate control system. The in-car temperature reading BD25 display will indicate actual sensor reading.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks to see if open circuit reading is due to circuit or sensor. If open circuit reading changes to a shorted circuit reading after jumping sensor terminals, BCM and wiring are okay.

Test Number 2) By applying a ground to various points in circuits, an open can be isolated by observing whether parameter display can be changed from open reading to shorted reading.

Test Number 3) Checks to see if shorted circuit reading is due to circuit or sensor. If shorted circuit reading changes to an open circuit reading after disconnecting sensor, BCM and wiring are okay.

Buick Riviera 1990 - Note on Intermittents

If Code B113 is set with Code B115, check for an intermittent open in circuit No. 736. If an intermittent Code B113 is being set, manipulate related wiring while observing BD25 display. If failure is induced, reading will jump from its normal value to a reading outside the range of -29?F (-34?C) to 209?F (85?C).

If value indicated by BD25 display is not reasonably close to actual temperature of air at sensor, check for poor terminal contact or replace sensor.

Fig. 31: Buick Riviera 1990 - Component Locations - Code B113: Circuit Diagram

Fig. 32: Buick Riviera 1990 - Component Locations - Code B113: Flow Chart In-Car Temp Sensor Circuit

Buick Riviera 1990 - CODE B115: SUN LOAD SENSOR CIRCUIT

The sun load sensor is a thermistor that controls signal voltage to BCM. The BCM applies and monitors voltage on circuit No. 590 to sensor. When sensor is cold, its resistance is high, therefore, BCM will see a high monitored voltage. As sensor warms, its resistance becomes less and monitored voltage is pulled low through sensor ground, circuit No. 736. This monitored voltage will vary between 5 volts (open circuit) and zero volts (shorted circuit).

Code B115 will set if ignition is on, outside temperature sensor has not failed and reads greater than 32?F (0?C), and signal voltage indicates less than -29?F (-34?C), which is open circuit voltage, or greater than 209?F (85?C), which is shorted circuit voltage. During time failure is present, a substitute temperature reading will be used to allow continued operation of climate control system. The sun load temperature reading BD32 display will indicate actual sensor reading.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks to see if open circuit reading is due to circuit or sensor. If open circuit reading changes to a shorted circuit reading after jumping sensor terminals, BCM and wiring are okay.

Test Number 2) By applying a ground to various points in circuits, an open can be isolated by observing whether parameter display can be changed from open reading to shorted reading.

Test Number 3) Checks to see if shorted circuit reading is due to circuit or sensor. If shorted circuit reading changes to an open circuit reading after disconnecting sensor, BCM and wiring are okay.

Buick Riviera 1990 - Note on Intermittents

If an intermittent Code B115 is being set, check B115 snap data value for sun load temperature, BD32 display. If BD32 display value is less than -29?F (-34?C), code resulted from an open in circuit No. 590, circuit No. 736 or sun load temperature sensor. If BD32 display value is greater than 85?C, code resulted from a short to ground on circuit No. 590 or shorted sun load temperature sensor. Manipulate related wiring while observing BD32 display. If failure is induced, reading will jump from its normal value to a reading outside the range of -29?F (-34?C) to 209?F (85?C).

If value displayed by BD32 display is not reasonably close to a corresponding thermometer reading, check for poor terminal contact or replace sensor.

Fig. 33: Buick Riviera 1990 - Component Locations - Code B115: Circuit Diagram

Fig. 34: Buick Riviera 1990 - Component Locations - Code B115: Flow Chart Sun Load Sensor Circuit

Buick Riviera 1990 - CODE B119: TWILIGHT PHOTOCELL CIRCUIT

NOTE:

Ensure nothing is covering sensor before following this procedure.

The twilight sensor uses a photocell to control signal voltage to BCM. The BCM applies and monitors voltage on circuit No. 278 to sensor. When sensor detects darkness, its resistance is high, therefore, BCM will see a high monitored voltage. As sensor detects light, its resistance becomes less and monitored voltage is pulled low through ground circuit No. 736. This signal voltage will vary between 5 volts (open circuit) and zero volts (shorted circuit).

Code B119 will set if ignition is on and signal voltage indicates more than 97 percent, open circuit voltage or less than 3 percent, which is shorted circuit voltage). During time failure is present, a substitute light reading (indicating darkness) will be used to allow continued operation of headlights. The measure of light reading, BD44 display, will indicate actual sensor reading.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks to see if open circuit is due to circuit or sensor. If open circuit reading changes to a shorted circuit reading after jumping sensor terminals, BCM and wiring are okay.

Test Number 2) By applying a ground to various points in circuits, an open can be isolated by observing whether parameter display can be changed from open reading to shorted reading.

Test Number 3) Checks to see if shorted circuit reading is due to circuit or sensor. If shorted circuit reading changes to an open circuit reading after disconnecting sensor, BCM and wiring are okay.

Buick Riviera 1990 - Note on Intermittents

If an intermittent Code B119 is being set, manipulate related wiring while observing BD44 display. If failure is induced, reading will jump from its normal value to a reading outside the range of 3-97 percent. Make certain owner is aware not to cover sensor.

Fig. 35: Buick Riviera 1990 - Component Locations - Code B119: Circuit Diagram

Fig. 36: Buick Riviera 1990 - Component Locations - Code B119: Flow Chart Twilight Photocell Circuit

Buick Riviera 1990 - CODE B120: TWILIGHT DELAY POTENTIOMETER

The twilight delay uses a potentiometer to control signal voltage to BCM. The BCM supplies voltage on circuit No. 705 to resistor in left switch assembly and returns as a ground to BCM on circuit No. 736. The wiper provides voltage signal to BCM on circuit No. 271. When slider is moved toward maximum position (maximum delay), resistance is low, therefore BCM will see a high signal voltage. As slider is moved toward minimum position (minimum delay), its resistance increases and signal voltage decreases. This signal voltage will vary between zero volts (open or grounded circuit) and 5 volts (shorted to voltage circuit).

Code B120 will set if vehicle is equipped with twilight sentinel, ignition is on and signal voltage indicates less than 2 percent (open or grounded circuit) or greater than 98 percent (shorted to voltage). During time failure is present, a substitute delay time (minimum delay) will be implemented, allowing continued operation of twilight system. The reading from potentiometer BD43 display will indicate actual reading.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) BD43 displays twilight delay time. The normal range is 2-98 percent.

Test Number 2) Checks to see if open or grounded circuit reading is due to circuit or switch. If open or grounded circuit reading changes from a short to voltage reading after jumping switch assembly terminals, BCM and wiring are okay.

Test Number 3) Measuring between circuit No. 705 (5 volts) and circuit No. 736 will determine if circuits No. 705 or 271 is open or shorted to ground.

Buick Riviera 1990 - Note on Intermittents

If an intermittent Code B120 is being set, check B120 snap data value for twilight delay BD43 display. If BD43 display value is greater than 98 percent, code resulted from an open in circuit No. 271, circuit No. 736 or left switch pod. If BD43 display value is less than 2 percent, code resulted from a short in left switch pod. Manipulate related wiring while observing BCM data parameter BD43 display. If failure is induced, reading will jump from its normal value to a reading outside range of 2-98 percent.

Fig. 37: Buick Riviera 1990 - Component Locations - Code B120: Circuit Diagram

Fig. 38: Buick Riviera 1990 - Component Locations - Code B120: Flow Chart Twilight Delay Potentiometer

Buick Riviera 1990 - CODE B120 & B122: TWILIGHT DELAY & PANEL DIMMING

Because both potentiometers use the same power and ground, problem is most likely in power or ground circuits when both codes are stored.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks to see if open or grounded circuit reading is due to circuits or switch assembly. If voltage can be read across circuits No. 705 and 736 after disconnecting switch assembly, BCM and wiring are okay.

Test Number 2) Checks for 5-volt reference at switch. If 5 volts is present, circuit No. 736 is open. If circuit No. 736 is open, open will be between terminal B4 on left switch assembly and cavity B2 on dash instrument panel transition connector.

Test Number 3) If circuit No. 705 is suspected of being grounded, remove HVAC programmer and BCM connectors prior to making a ground check.

Test Number 4) If there is no ground in circuit No. 705, replace HVAC programmer or BCM.

Buick Riviera 1990 - Note on Intermittents

If an intermittent Code B120 and B122 is being set, check B120 snap data value for twilight delay BD43 display. If BD43 display value is greater than 98 percent, code resulted from an open in circuit No. 736 or left switch pod. If BD43 display value is less than 2 percent, code resulted from a short in circuit No. 705 or short in left switch pod. Manipulate related wiring while observing BD43 display. If failure is induced, reading will jump from its normal value to a reading outside the range of 2-98 percent.

Fig. 39: Buick Riviera 1990 - Component Locations - Code B120 & 122: Circuit Diagram

Fig. 40: Buick Riviera 1990 - Component Locations - Code B120 & 122: Flow Chart Twilight Delay & Panel Dimming

Buick Riviera 1990 - CODE B121: TWILIGHT ENABLE SWITCH CIRCUIT

The twilight enable switch uses the same physical control as delay pot. Inside left switch assembly, enable switch contacts close as soon as time delay slider is moved off of its extreme minimum (off) position. The BCM supplies a voltage on circuit No. 304 to switch. When slider is moved from off position, switch contacts close and signal voltage is pulled low through ground circuit No. 804.

Code B121 will set if vehicle is equipped with twilight sentinel, twilight delay pot has not failed (Code B120), and signal voltage is high when delay slider is greater than 2 seconds delay (twilight sentinel on), or signal voltage is low when delay slider is less than 3 seconds (twilight sentinel off). During time failure is present, twilight sentinel will operate based on delay input. Whenever delay is greater than 2 seconds, BCM will assume twilight sentinel is on.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) BI82 displays voltage state of circuit at BCM. These conditions can be observed in BI82 display as readings of HI or LO when slider is moved.

Test Number 2) Checks to see if HI reading is due to circuit or switch assembly. If display changes from HI to LO when switch assembly is disconnected, both BCM and wiring are okay.

Test Number 3) Checks to see if HI reading is due to an open circuit No. 304 or circuit No. 804. If display changes from HI to LO when a known good ground is provided, circuit No. 804 is open.

Buick Riviera 1990 - Note on Intermittents

If an intermittent Code B121 is being set, manipulate related. When BI82 displays change-of-state, an "X" will be indicated. Check circuit for an intermittent open or short.

Fig. 41: Buick Riviera 1990 - Component Locations - Code B121: Circuit Diagram

Fig. 42: Buick Riviera 1990 - Component Locations - Code B121: Flow Chart Twilight Enable Switch Circuit

Buick Riviera 1990 - CODE B122: PANEL DIMMING POTENTIOMETER CIRCUIT

The panel dimmer is a potentiometer that indicates desired display intensity to BCM. The BCM supplies voltage on circuit No. 705 and a ground on circuit No. 736 to potentiometer in left switch assembly. The wiper provides voltage signal to BCM on circuit No. 686, indicating position of slider and delay time. When slider is moved toward minimum position, its resistance increases and signal voltage decreases.

Code B122 will set, if signal voltage indicates less than 2 percent (open or grounded circuit), or greater than 98 percent (shorted to voltage). During time failure is present, a substitute delay time will be implemented to allow continued operation of interior lighting. The reading from potentiometer BD42 display will indicate actual reading.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks to see if open or grounded circuit reading is due to circuits or switch assembly. If open or grounded circuit reading changes to a short to voltage reading, after jumpering switch assembly terminals, BCM and wiring are okay.

Test Number 2) Measuring voltage between circuit No. 705 (5 volts) and circuit No. 736 will determine if problem is in circuits No. 705 or 686.

Test Number 3) Checks to see if short to voltage circuit reading is due to circuit or an open in circuit No. 736 and switch assembly. If a short to voltage reading changes to an open circuit reading, after disconnecting switch assembly, BCM and circuit No. 686 are okay.

Buick Riviera 1990 - Note on Intermittents

If an intermittent Code B122 is being set, check B122 snap data value for twilight delay BD42 display. If BD42 display value is greater than 98 percent, code resulted from an open in circuit No. 271, circuit No. 736 or left switch pod. If BD42 display value is less than 2 percent, code resulted from a short in left switch pod. Manipulate related wiring while observing BD42 display. If failure is induced, reading will jump from its normal value to a reading outside the range of 2-98 percent.

Fig. 43: Buick Riviera 1990 - Component Locations - Code B122: Circuit Diagram

Fig. 44: Buick Riviera 1990 - Component Locations - Code B122: Flow Chart Panel Dimming Potentiometer Circuit

Buick Riviera 1990 - CODE B123, PANEL LAMP SWITCH CIRCUIT

Inside left switch assembly, panel lamp switch contacts close when dimming slider is moved to its extreme maximum position. The BCM supplies a voltage on circuit No. 685 to switch. When signal is pulled to ground, BCM turns courtesy light on.

Code B123 will set if panel dimming pot has not failed and BCM sees circuit No. 685 grounded while dimmer switch position was less than a value for maximum panel light brightness. A grounded circuit No. 685 will not only set Code B123, but will also turn courtesy lights on at all times and drain battery.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) BI01 display, dimmer switch input, will read LO if dimming slider is at maximum "up" position. BI01 display will read HI if dimming slider is not at maximum position.

Test Number 2) By removing switch assembly, a shorted switch can be detected by observing BI01 display.

Test Number 3) By removing BCM connector, short to ground can be isolated as being wire or BCM.

Buick Riviera 1990 - Note on Intermittents

If circuit No. 685 were intermittently grounded, Code B123 could be stored. Manipulate circuit No. 685 while observing BI01 display with dimmer at a low setting. If short occurs, value will switch from HI to LO.

Also check BD42 display. Cycle panel dimming control from minimum to maximum. If BD42 display does not range between 2-98 percent, or never reads more than 75 percent, replace left switch assembly.

Fig. 45: Buick Riviera 1990 - Component Locations - Code B123: Circuit Diagram

Fig. 46: Buick Riviera 1990 - Component Locations - Code B123: Flow Chart Panel Lamp Circuit

Buick Riviera 1990 - CODE B124: VEHICLE SPEED SENSOR (VSS) CIRCUIT PROBLEM

The vehicle speed sensor uses a Permanent Magnet (PM) generator to generate an electrical signal representative of vehicle speed. This signal is sent to ECM through circuit No. 400 (VSS high) and circuit No. 401 (VSS low), where ECM buffers and amplifies signal. Output voltage of generator can be read by using a digital voltmeter on 2-volt AC scale while rotating generator drive (front wheels). Code B124 will set if following conditions are present for 30 seconds:

• Ignition on
• No Code B334
• Transaxle in 4th gear
• Vehicle speed is zero
• Condition occurs for at least 2 seconds

Or if following conditions exist:

• Ignition on
• No Code B334
• Vehicle speed is zero
• Code B124 currently set

During time failure is present, cruise control and continuous compressor at idle will be disabled. Vehicle speed reading BD60 display will indicate actual sensor reading.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) Since ECM amplifies and buffers speed signal before it is sent to BCM, Code EO24 in ECM may set along with Code B124 in BCM. If Code B124 sets with a Code EO24, refer to diagnosis for Code EO24.

NOTE:

Since Code EO24 is not set, problem is not actual sensor. Problem must be with ECM, BCM or dedicated speed data line circuit No. 437 between ECM and BCM.

Buick Riviera 1990 - Note on Intermittents

If an intermittent Code B124 is being set, manipulate related wiring while observing BD60 display. If failure is induced, reading will jump from a normal value to zero MPH.

Fig. 47: Buick Riviera 1990 - Component Locations - Code B124: Circuit Diagram

Fig. 48: Buick Riviera 1990 - Component Locations - Code B124: Flow Chart VSS Circuit Problem

Buick Riviera 1990 - CODE B132: ENGINE OIL PRESSURE SENSOR CIRCUIT FAULTY

The oil pressure indicator is a variable resistor used to indicate oil pressure to BCM. The BCM supplies voltage on circuit No. 313 to sensor. When the engine is not running (oil pressure low), sensor resistance is low. When the engine is running (increased oil pressure), sensor resistance becomes high. The signal voltage will vary between 5 volts (open circuit) and zero volts (short circuit).

Code 132 will set if engine is running and the signal voltage indicates greater than 80 psi for at least 2 seconds. As actual engine oil pressure will never be that high, code indicates an open circuit, faulty sensor or faulty BCM.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks to see if open circuit reading is due to circuit or sensor. If open circuit reading changes to a shorted circuit reading after jumping sensor terminals, BCM and wiring are okay.

Test Number 2) By applying a ground to various points in the circuits, an open can be isolated by observing whether the parameter display changes to a short circuit reading.

Buick Riviera 1990 - Note on Intermittents

If an intermittent Code B132 is being set, manipulate the related wiring while observing BCM data parameter BD71. If the failure is induced, the reading will change to a high oil pressure.

Fig. 49: Buick Riviera 1990 - Component Locations - Code B132: Circuit Diagram

Fig. 50: Buick Riviera 1990 - Component Locations - Code B132: Flow Chart Engine Oil Pressure Sensor Circuit Faulty

Buick Riviera 1990 - CODE B333: LOSS OF (SIR) DATA

Code B333 will be set if communication between DERM (SIR controller) and BCM is lost. When this code is set, ELECTRICAL PROBLEM and INFLATABLE RESTRAINT warning lights will illuminate.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks if other data line components are experiencing communications problems.

Test Number 2) Checks status of data line at compass module. Normal data line voltage is .1-4.5 volts.

Buick Riviera 1990 - Note on Intermittents

If an intermittent Code B333 is being stored, manipulate relating wiring at DERM (SIR controller). An ELECTRICAL PROBLEM message indicates loss of data and may help locate fault.

Fig. 51: Buick Riviera 1990 - Component Locations - Code B333: Circuit Diagram

Fig. 52: Buick Riviera 1990 - Component Locations - Code B333: Flow Chart Loss of SIR Data

Buick Riviera 1990 - CODE B334: LOSS OF ECM DATA

Code B334 will set if communication between ECM and BCM is lost. If the BCM remains powered and only serial communication is lost, the vehicle will still run, however with ignition key on (engine not running), an ELECTRICAL PROBLEM message will illuminate.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) If the ECM looses power or ground, code will set since ECM cannot communicate. It is important to note that engine will not start.

Test Number 2) Since prior checks eliminated an open circuit, fault is poor terminal contact at ECM terminal No. 2A8, a faulty CALPAK connection or a faulty ECM.

Buick Riviera 1990 - Note on Intermittents

If an intermittent Code B334 is being set, manipulate the related wiring at ECM. With the ignition key on (engine not running), an ELECTRICAL PROBLEM warning light will indicate loss of ECM communication, and possibly help to isolate the intermittent without having to look for the code. Also check ECM and CALPAK connections.

Fig. 53: Buick Riviera 1990 - Component Locations - Code B334: Circuit Diagram

Fig. 54: Buick Riviera 1990 - Component Locations - Code B334: Flow Chart Loss of ECM Data

Buick Riviera 1990 - CODE B335: LOSS OF ECCP SERIAL DATA

This code can only be viewed as a "history" code, because if it was current, service diagnostics could not be entered. Most likely the ECC controls for heating and A/C will also be inoperative when the loss of serial data occurs.

Since the serial data lines are redundant, a double open in the circuit No. 800 has to occur to set this code. However, the code will also set for a single open in the power or ground supply to the ECCP.

NOTE:

Loss of ECCP ground will cause data line circuit No. 800 to be tied to system voltage, disabling all vehicle self-diagnostics.

Fig. 55: Buick Riviera 1990 - Component Locations - Code B335: Circuit Diagram

Fig. 56: Buick Riviera 1990 - Component Locations - Code B335: Flow Chart Loss of ECCP Data

Buick Riviera 1990 - CODE B336: LOSS OF IPC SERIAL DATA

This code can only be viewed as a "history" code because if it was current, service diagnostics could not be entered. Since serial data, CPS power and ground terminals are redundant, it would take a double open in any of those circuits to set the code. A single intermittent open in circuit No. 750 would also set this code.

If codes are intermittent, careful checking of all terminal contacts is required prior to any parts being replaced.

Fig. 57: Buick Riviera 1990 - Component Locations - Code B336: Circuit Diagram

Code B336 indicates an intermittent loss of IPC data has occurred. Should intermittent problems persist, Check the following circuits for opens or poor terminal contact. If intermittent problem are still present, replace IPC.

Buick Riviera 1990 CODE B336 CIRCUIT

Circuit	IPC Terminal
Serial Data	AJ & AH
IGN 3	BG
CPS Power	AA & BL
Ground	AL & BA

Fig. 58: Buick Riviera 1990 - Component Locations - Code B336: IPC Harness View

Buick Riviera 1990 - CODE B337: LOSS OF HVAC PROGRAMMER DATA

Code B337 will set if communication between the programmer and BCM is lost. This can occur if the HVAC loses ignition, ground or both serial data circuits.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks for power and ground up to the programmer. The test light should be on when connected from ignition source to both grounds.

Test Number 2) Since power and ground are available to the programmer, the source for failure is either a double open in the circuit No. 800 or faulty terminal contacts.

Fig. 59: Buick Riviera 1990 - Component Locations - Code B337: Circuit Diagram

Fig. 60: Buick Riviera 1990 - Component Locations - Code B337: Flow Chart Loss of HVAC Programmer Data

Buick Riviera 1990 - SERIAL DATA CIRCUIT MULTIPLE INTERMITTENT CODES

Fig. 61: Buick Riviera 1990 - Component Locations - Serial Data Circuit Diagram

Fig. 62: Buick Riviera 1990 - Component Locations - Serial Data Flow Chart

Buick Riviera 1990 - CODE B410: CHARGING SYSTEM CIRCUIT FAULT

The generator on this vehicle has fault detection capability built into the regulator. The BCM supplies 12 volts on circuit No. 25 ("I" terminal) and monitors the field voltage on circuit No. 23 ("F+" terminal).

Code B410 will set if the following conditions exist:

• Engine running
• Generator enable line is low

Or if the following conditions exist:

• Engine running
• Generator enable line high
• Generator field input is less than 2 percent

Or if the following conditions exist:

• Ignition on, engine not running
• Generator enable line is high

Or if the following conditions exist

• Ignition on, engine not running
• Generator enable line is low
• Generator field input is less than 2 percent

Code B140 will cause the ELECTRICAL PROBLEM warning light to illuminate.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) BI51 displays generator signal voltage as HI or LO, depending on the voltage state at BCM. Normally, with key on and engine off, circuit No. 25 voltage will be pulled low by the generator and BI51 will read LO.

Test Number 2) Checks to see if LO reading is due to circuit No. 25 or the generator. If display reading changes from LO to HI when the generator is disconnected with engine running, BCM and circuit No. 25 are okay.

Test Number 3) Checks to see if fault is due to BCM or circuit No. 25.

Test Number 4) BD51 displays the amount of generator field activity. Under normal conditions, a reading less than 7 percent would indicate a fault in field circuit or BCM.

Test Number 5) Removing the generator connector will determine if fault is due to generator or an open in circuit No. 25, including BCM and interface connector.

Buick Riviera 1990 - Note on Intermittents

If an intermittent condition exists, check B410 snap data parameters BD61 and BI51. Also check for the following conditions:

• If BD61 is under 500 RPM and BI51 is high, check for an intermittent open in circuit No. 25.
• If BD61 is under 500 RPM and BI51 is LO, check for an intermittent short to ground in circuit No. 23.
• If BD61 is over 500 RPM and BI51 is HI, check for an intermittent short to ground in circuit No. 23.
• If BD61 is over 500 RPM and BI51 is low, check for an intermittent short to ground in circuit No. 25.

Also perform the battery and charging system checks, to ensure proper operation of these components.

Fig. 63: Buick Riviera 1990 - Component Locations - Code B410: Circuit Diagram

Fig. 64: Buick Riviera 1990 - Component Locations - Code B410: Flow Chart Charging System Circuit Fault

Buick Riviera 1990 - CODE B411 OR B412: BATTERY VOLTAGE TOO HIGH OR TOO LOW

The BCM monitors ignition "1" voltage on terminal No. 3D7 as a reference for fuel control. Code B411 will set when ignition is on and the engine RPM is greater than 800 and the BCM sees an ignition "1" reference voltage of less than 10.6 volts. Code B412 will be set if the BCM sees voltage over 16 volts. Both B411 and B412 will cause the GENERATOR PROBLEM message to be displayed on IPC.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) BD50 displays battery voltage. The normal range is 10.6-16 volts.

Test Number 2) Checks to see if low voltage reading is due to circuit or battery. With engine running, and if voltage is less than 10 volts, BCM and wiring are okay.

Test Number 3) Checks to see if low voltage reading is due to circuit or BCM. If voltage reading at BCM is less than 10.6 volts, BCM is okay.

Test Number 4) Checks to see if high voltage reading is due to generator or faulty BCM.

Test Number 5) Checks to see if charging voltage goes too high with higher engine RPM or electrical load.

Buick Riviera 1990 - Note on Intermittents

If an intermittent Code B411 or B412 is being set, observe BD50 display. This battery voltage reading is monitored from 15-amp ISO IGN 1 fuse, fuel level reference voltage. If code is being set due to a high current draw in a certain vehicle component, this can be observed by reading BD50 display. Operate various components while watching for reading to drop to less than 10 volts or increase to greater than 16 volts. Code B411 could be caused by an intermittent open in circuit No. 39, which may be observed by manipulating wire to BCM while observing BD50 voltage for a drop below 10 volts.

Fig. 65: Buick Riviera 1990 - Component Locations - Code B411 or 412: Circuit Diagram

Fig. 66: Buick Riviera 1990 - Component Locations - Code B411 or 412: Flow Chart Battery Volt High or Low

Buick Riviera 1990 - CODE B420: COURTESY - TWILIGHT LIGHT RELAY CIRCUITS

The BCM operates the twilight sentinel (if equipped), retained accessory power, HI/LO beam and courtesy lamp relays by providing grounds for coils. When relay(s) are on, BCM output will be low and when relay(s) are off, BCM output will be high.

Code B420 will set if output voltage at BCM is high when a low has been commanded, or output voltage is low when high has been commanded. The Reatta will not be equipped with twilight sentinel and only uses one relay for HI/LO beam control.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) To determine which system has failed (courtesy lamps, twilight, if equipped, HI/LO beams, or retained accessory power), select BCM output function in diagnostics. As individual outputs cycle on and off, observe their actual operation.

Buick Riviera 1990 - Note on Intermittents

Since all 4 (or 3 in the case of Reatta) groups of relays can cause an intermittent condition, see NOTE ON INTERMITTENTS (in each CODE B420 Cont.) for each of the relays.

Fig. 67: Buick Riviera 1990 - Component Locations - Code B420: Circuit Diagram

Fig. 68: Buick Riviera 1990 - Component Locations - Code B420: Flow Chart Twilight Light Relay Circuit

Buick Riviera 1990 - CODE B420: COURTESY LAMP RELAY CIRCUITS

If courtesy lamps did not cycle on and off when BO04 display was selected, this is the relay that set Code B420.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks to see if fault is due to an open circuit or a short to ground in circuit. If courtesy lamps are always on, there is a short to ground in control circuit and if courtesy lamps never turn on, there is an open in one of the circuits.

Test Number 2) Checks to see if short to ground is due to circuit or BCM.

Test Number 3) Checks to see if open circuit is due to circuit or relay.

Test Number 4) Checks to see if open circuit is on power or ground side of circuit.

Test Number 5) Checks to see if open circuit is in wiring or BCM.

Buick Riviera 1990 - Note on Intermittents

If an intermittent Code B420 is being set. Manipulate related wiring in output function and watch for relays to cycle. Since this code only monitors the control (winding) side of relays, it is possible for the relay to fail and/or circuits on relay contacts. This would prevent courtesy lamp from operating, without setting this code.

Fig. 69: Buick Riviera 1990 - Component Locations - Code B420: Circuit Diagram

Fig. 70: Buick Riviera 1990 - Component Locations - Code B420: Flow Chart Courtesy Lamp Relay Circuit

Buick Riviera 1990 - CODE B420: TWILIGHT RELAY CIRCUITS (OPTIONAL ON RIVIERA ONLY)

If headlights and parking lights did not cycle on and off when BO05 was selected, this is the system that set Code B420.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks to see if fault is due to an open circuit or a short to ground in circuit. If headlights and parking lights are always on, there is a short to ground in control circuit and if headlights and parking lights never turn on, there is an open in one of the circuits.

Test Number 2) Checks to see if short to ground is due to crank circuit or control circuit.

Test Number 3) Checks to see if short to ground is due to circuit or BCM.

Test Number 3a) Checks to see if short in crank circuit is due to relay or wiring.

Test Number 4) Checks to see if open circuit is due to circuit or BCM.

Test Number 5) Checks to see if open circuit is on power or ground side of relay.

Buick Riviera 1990 - Note on Intermittents

If an intermittent Code B420 is being set. Manipulate related wiring in output function and watch for relays to cycle. Since this code only monitors the control (winding) side of relays, it is possible for the relay to fail and/or circuits on relay contacts. This would prevent courtesy lamp from operating, without setting this code. As long as one or more of the relay windings are okay, code will not set. BCM cannot tell the difference between operating one or 2 relays.

Fig. 71: Buick Riviera 1990 - Component Locations - Code B420: Circuit Diagram

Fig. 72: Buick Riviera 1990 - Component Locations - Code B420: Flow Chart Twilight Relay Circuit (Optional On Riviera Only)

Buick Riviera 1990 - CODE B420: HI/LO BEAM RELAY CIRCUIT (RIVIERA ONLY)

If HI/LO beams did not cycle on and off when BO06 was selected, this is the system that set Code B420.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks to see if fault is due to an open circuit or a short to ground in circuit. If HI beams are always on, there is a short to ground in control circuit. If LO beams are always on, there is an open in one of the circuits.

Test Number 2) Checks to see if short to ground is due to circuit or BCM.

Test Number 3) Checks to see if open circuit is due to circuit or BCM.

Test Number 4) Checks to see if open circuit is on power or ground side of relay.

Buick Riviera 1990 - Note on Intermittents

If an intermittent Code B420 is being set. Manipulate related wiring in output function and watch for relays to cycle. Since this code only monitors the control (winding) side of relays, it is possible for the relay to fail and/or circuits on relay contacts preventing HI/LO beam operation, without setting this code.

Fig. 73: Buick Riviera 1990 - Component Locations - Code B420: Circuit Diagram

Fig. 74: Buick Riviera 1990 - Component Locations - Code B420: Flow Chart Hi/Low Beam Relay Circuit (Riviera Only)

Buick Riviera 1990 - CODE B420: HI/LO BEAM RELAY CIRCUIT (REATTA ONLY)

If HI/LO beams did not cycle on and off when BO06 was selected, this is the system that set Code B420.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks to see if fault is due to an open circuit or a short to ground in circuit. If HI beams are always on, there is a short to ground in control circuit. If LO beams are always on, there is an open in one of the circuits.

Test Number 2) Checks to see if short to ground is due to circuit or BCM.

Test Number 3) Checks to see if open circuit is due to circuit or relay.

Test Number 4) Checks to see if open circuit is on power or ground side of relay.

Test Number 5) Checks to see if open circuit is in wiring or BCM.

Buick Riviera 1990 - Note on Intermittents

If an intermittent Code B420 is being set. Manipulate related wiring in output function and watch for relays to cycle. Since this code only monitors the control (winding) side of relays, it is possible for the relay to fail and/or circuits on relay contacts preventing HI/LO beam operation, without setting this code.

Fig. 75: Buick Riviera 1990 - Component Locations - Code B420: Circuit Diagram

Fig. 76: Buick Riviera 1990 - Component Locations - Code B420: Flow Chart Hi/Low Beam Relay Circuit (Reatta Only)

Buick Riviera 1990 - CODE B420: FOG LAMP (DRL) RELAY CIRCUIT (REATTA ONLY)

If fog lamps did not cycle on and off when BO12 was selected, this is system that set Code B420.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks if fault is due to an open circuit or short to ground in the circuit. If fog lamps are always on, there is a short to ground in control circuit. If fog lamps are always off, there is an open in one of the circuits.

Test Number 2) Checks to see if short to ground is due to circuit or BCM.

Test Number 3) Checks to see if open circuit is caused by circuit or relay.

Test Number 4) Checks to see if open circuit is on power or ground side of relay.

Test Number 5) Checks to see if open circuit is in wiring or BCM.

Buick Riviera 1990 - Note on Intermittents

If an intermittent Code B420 is being set. Manipulate related wiring in output function and watch for relays to cycle. Since this code only monitors the control (winding) side of relays, it is possible for the relay to fail and/or circuits on relay contacts preventing fog lamp operation, without setting this code.

Fig. 77: Buick Riviera 1990 - Component Locations - Code B420: Circuit Diagram

Fig. 78: Buick Riviera 1990 - Component Locations - Code B420: Flow Chart Fog Lamp (DRL) Relay Circuit (Reatta Only)

Buick Riviera 1990 - CODE B420: RETAINED ACCESSORY POWER RELAY CIRCUIT

Whenever ignition is turned on, BCM will ground circuit No. 707, energizing both Retained Accessory Power (RAP) relays. This will provide power to power window and sunroof switches, radio, windshield wiper switch, trunk and glove box release switches, through circuit No. 660. If these functions do not work after RAP has been energized (by turning ignition on and off), with doors closed, or they remain working after door is opened, this is the system that set Code B420 (normal operation RAP timeout is 10 minutes). Circuit No. 70 is used as a back-up to provide power to windows if there is a circuit fault (ignition has to be on). Circuit No. 41 is also used as a back-up, but powers other functions when ignition is in accessory position since BCM is inactive and cannot ground circuit No. 707.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks to see if fault is with RAP system or just a problem with one or more of the functions RAP provides power to.

Test Number 2) Checks to see if fault is due to an open circuit or a short to ground in circuit. If the different functions always work, there is a short to ground in control circuit. If different functions do not work with RAP activated, there is an open in one of the circuits.

Test Number 3) Checks to see if short to ground is due to circuit or BCM.

Test Number 4) Checks to see if open circuit is due to circuit or BCM.

Test Number 5) Checks to see if open circuit is on power or ground side of relay.

Buick Riviera 1990 - Note on Intermittents

If an intermittent Code B420 is being set. Manipulate related wiring in output function and watch for relays to cycle. Since this code only monitors the control (winding) side of relays, it is possible for the relay to fail and/or circuits on relay contacts, preventing RAP operation, without setting this code. The BCM cannot tell the difference between operating one or 2 relays.

Fig. 79: Buick Riviera 1990 - Component Locations - Code B420: Circuit Diagram

Fig. 80: Buick Riviera 1990 - Component Locations - Code B420: Flow Chart Retained Accessory Power Relay Circuit

Buick Riviera 1990 - CODE B440, AIR MIX VALVE (DOOR) CIRCUIT PROBLEM

Code B440 is set by BCM if commanded air mix door position is between 30-80 percent, but actual air mix door position is not within 2 percent of commanded position for 60 seconds. The BCM commands the programmer to move air mix valve (door) over data circuit No. 800. With ignition on, BCM supplies 5 volts on circuit No. 705 and ground on circuit No. 736. A motor in programmer drives air mix valve (door). The BCM monitors door position through a feedback pot on DC motor which varies between zero and 5 volts depending on air mix door position. If air mix valve (door) feedback indicates it is near hot or cold extreme, code will not set since mix door may be at its limit of travel and not able to reach commanded door position.

Operation of air mix valve (door) can be evaluated in BCM display by actual air mix valve (door) position (BD23 display ACT MIX DR) while changing the programmer number (override BS01 display PROGRAM NO).

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) BD23 display indicates actual air mix valve (door) position. The normal range is between 1-99 percent. BCM override value BS01 display is for program number.

Test Number 2) Checks to see if fault could be due to 5-volt reference and ground circuit, or sensor circuit.

Test Number 3) Checks to see if fault is due to programmer or sensor circuit.

Test Number 4) Checks to see if fault is due to circuit or BCM.

Test Number 5) This step checks to see if open circuit reading is due to circuit No. 736 or circuit No. 705.

Buick Riviera 1990 - Note on Intermittents

If an intermittent Code B440 is being set, check B440 snap data BD23 display. If it was zero percent, check for an intermittent open in circuit No. 736. If it was 100 percent, check for an intermittent open in circuit No. 733 or circuit No. 705. If it was 1-99 percent, check for binding door movement throughout range of door travel and check for a poor ground circuit No. 803. Manipulate related wiring while observing actual air mix door position (BD23 display) movement. If failure is induced, valve (door) position will either stop or jump to an extreme value (zero to 100 percent). This will assist in isolating location of malfunction.

Exit diagnostics and select Max Heat (90?F) and Max Cool (60?F) using normal HVAC controls, waiting a minimum of 2 minutes in each mode to see if code sets.

Fig. 81: Buick Riviera 1990 - Component Locations - Code B440: Circuit Diagram

Fig. 82: Buick Riviera 1990 - Component Locations - Code B440: Flow Chart Air Mix Valve (Door) Circuit Problem

Buick Riviera 1990 - CODES B446, B447 & B448 REFRIGERANT SYSTEM PROBLEM

If system refrigerant state of charge falls below approximately one third its capacity, BCM will detect this condition and display LOW A/C REFRIGERANT or VERY LOW A/C REFRIGERANT message to warn driver.

Code B446 will set if the low side temperature drops too quickly during compressor engagement. Code B447 will set if low side temperature drops much too quickly during compressor engagement or the low refrigerant pressure switch opens during compressor engagement. Code B448 will set if the low refrigerant pressure switch remains open for greater than 3 minutes.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) BCM input value BI08 displays voltage state of circuit at BCM.

Test Number 2) Checks to see if open circuit reading is due to circuit or switch.

Test Number 3) Checks to see if fault is on ignition side or BCM side of switch circuit.

Test Number 4) This step checks to see if fault is due to pressure switch or a low refrigerant charge.

Fig. 83: Buick Riviera 1990 - Component Locations - Code B446, B447 & B448: Circuit Diagram

Fig. 84: Buick Riviera 1990 - Component Locations - Code B446, B447 & B448: Flow Chart Refrigerant System Problem (1 of 2)

Buick Riviera 1990 - CODES B446, B447 & B448 (CONTINUED)

It has been determined from previous chart that problem is not in low refrigerant pressure switch circuit.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) This is a test to determine if A/C low refrigerant pressure switch opens while compressor is running. If BI08 display remains high during compressor engagement, then system fault is due to refrigerant.

Test Number 2) This checks if switch is opening due to low refrigerant pressure charge or switch.

Buick Riviera 1990 - Note on Intermittents

If codes B446 and B447 are both set, check low side temperature sensor and circuitry. If okay, evacuate and recharge system.

If codes B447 and B448 are both set, check low refrigerant pressure switch and circuit.

Fig. 85: Buick Riviera 1990 - Component Locations - Code B446, B447 & B448: Circuit Diagram

Fig. 86: Buick Riviera 1990 - Component Locations - Code B446, B447 & B448: Flow Chart Refrigerant System Problem (2 of 2)

Buick Riviera 1990 - CODE B449, HIGH SIDE TEMPERATURE TOO HIGH

Code B449 is designed to disengage A/C compressor clutch in the event the high side refrigerant temperature exceeds 199?F (93?C). The A/C compressor clutch will reactivate once high side temperature falls to less than 199?F (93?C). Possible causes for excessively high A/C head pressures should be checked. Diagnose A/C system for refrigerant system performance.

Buick Riviera 1990 - CODE B450, COOLANT TEMPERATURE TOO HIGH

Code B450 is designed to disengage A/C compressor clutch if engine coolant temperature exceeds 261?F (126?C) and re-engage clutch when coolant temperature falls to less than 248?F (120?C). If Code EO14 is also stored, follow diagnosis for that code first. Engine overheating may accompany this code. If coolant temperature exceeds normal operating range, check for sources of overheating. Carefully check all sources of intermittent engine overheating, such as improper coolant fan operation, faulty belt or tension, low coolant level and restrictions or faulty hoses and/or routing.

Fig. 87: Buick Riviera 1990 - Component Locations - Code B450: Circuit Diagram High Side Temp Too High

Buick Riviera 1990 - CODE B482, ANTI-LOCK PRESSURE PROBLEM

This code indicates that brake pressure switch has indicated a low pressure condition to BCM. If Code B482 is set, and you are experiencing braking problems, diagnose ABS and normal braking system.

Code B482 sets whenever circuit No. 933 is pulled low to ground and remains low for 50 seconds. As soon as circuit No. 933 goes low, the Red BRAKE telltale will illuminate. The amber ANTI-LOCK telltale in the IPC is controlled only by ABS control unit.

Buick Riviera 1990 - Diagnosis

Enter diagnostics and note status of BI18. If BI18 is HI go to NOTE ON INTERMITTENTS. If BI18 is LO disconnect 5-pin hydraulic switch connector on ABS pump. If BI18 remains LO, repair short to ground on circuit No. 933. If BI18 changes to HI, refer to appropriate BRAKE SYSTEMS article for diagnosis of ABS system.

Buick Riviera 1990 - Note on Intermittents

If this code is set as "history" and you are not experiencing braking problems, look for a short to ground in circuit No. 933. Shorted conditions would have to be present for at least 50 seconds.

Fig. 88: Buick Riviera 1990 - Component Locations - Code B482: Circuit Diagram Anti-Lock Pressure Problem

Buick Riviera 1990 - CODE B552, BCM KEEP ALIVE MEMORY ERROR

Code B552 does not necessarily indicate a fault, but is a normal occurrence anytime battery power or ground to BCM has been interrupted. Code B552 cannot be cleared from memory in the normal manner. Code B552 can only be cleared if it is not current. Under normal conditions, code will become "history" under the following conditions:

• Ignition in lock position
• Wait for 5 seconds
• Ignition key on, re-enter diagnosis

After the above conditions have taken place, code should now be "history", and can be cleared in the normal manner. This code could be set if the system voltage drops to less than 8 volts at BCM terminal No. 1C9. Possible causes for this are faulty charging system, starter system, extreme cold weather and jump starting vehicle.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) This step is to change Code B552 from "current" to "history".

Test Number 2) Checks to see if Code B552 was set due to a fault during cranking mode.

Test Number 3) Checks for adequate system voltage at BCM terminal No. 1C10. System voltage must not drop to less than 8 volts during engine cranking. By removing fuel pump fuse, engine will not start and voltage during engine cranking can be observed.

Fig. 89: Buick Riviera 1990 - Component Locations - Code B552: Circuit Diagram

Fig. 90: Buick Riviera 1990 - Component Locations - Code B552: Flow Chart BCM Keep Alive Memory Error

Buick Riviera 1990 - CODE B556, ODOMETER (EE) PROM ERROR

Code B556 indicates that EEPROM, which records elapsed odometer mileage, is not being read by BCM. Usually along with Code 556, ERROR will be displayed in the odometer display. The EEPROM contains specific vehicle information such as vehicle ID number, season odometer mileage and certain vehicle options. Since this information is programmed for the specific vehicle in which it is installed, a EEPROM cannot be transferred from one vehicle to another. Check for proper EEPROM installation. If the EEPROM is properly installed, no bent pins, but Code B556 persists, replace EEPROM. Replacement EEPROMs must be obtained through an authorized Delco Service Center.

Fig. 91: Buick Riviera 1990 - Component Locations - Code B556: BCM Assembly

Buick Riviera 1990 - CODE B660, CRUISE CONTROL NOT IN DRIVE

Code B660 will set in the cruise control is engaged and BCM detects that gear selector is in Park or Neutral. This is done by the BCM based on ECM's input for Park and Neutral. During time failure is present, BCM will disengage cruise control.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) ECM input EI74 displays P/N gear status as HI or LO depending on voltage state at ECM. Display should read LO only when transaxle is in Park or Neutral. If it reads LO in any other gear selection, switch must be misadjusted or circuit No. 434 (including switch) is shorted to ground.

Test Number 2) Checks to see if short to ground reading is due to switch or circuit.

Buick Riviera 1990 - Note on Intermittents

This code was designed to prevent cruise control operation when vehicle is not in a forward gear. This code can set if operator selects Neutral, Reverse or Park when cruise control is engaged. This will cause cruise to drop out until operator re-engages cruise. If operator describes condition but did not move gear selector out of forward gears, check adjustment of gear selector switch and circuit No. 434 for intermittent short to ground.

Fig. 92: Buick Riviera 1990 - Component Locations - Code B660: Circuit Diagram & Flow Chart Cruise Control Not in Drive

Buick Riviera 1990 - CODE B663, CRUISE SPEED DIFFERENCE BETWEEN ACTUAL & SET IS TOO LARGE

Code B663 will set and disengage cruise control if actual speed is 30 MPH higher or lower than set speed. This code is used to set upper and lower limits for operation of the cruise control system, and can be set under normal conditions if operator accelerates, using accelerator pedal and drives 30 MPH greater than set speed. If operator experiences cruise drop out with this code set, but did not accelerate 30 MPH greater than set speed, a mechanical problem is indicated.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) BS05 displays a value representing servo position. The commanded range is normally 0-99 percent. If servo will not go to full stroke, vacuum supply, servo or vacuum brake release circuit is leaking.

Test Number 2) This step checks to see if vacuum leak is due to brake release valve and circuit, or servo and source of vacuum.

Test Number 3) This step checks to see if vacuum leak is due to vacuum source or servo.

Test Number 4) This step checks to see if fault is due to intermittent or slow vacuum leak.

Test Number 5) This step checks to see if fault is servo or brake vacuum release circuit.

Buick Riviera 1990 - Note on Intermittents

If Code B663 is setting intermittently, advise vehicle operator that overrunning the cruise control set speed by more than 30 MPH will cause this code to set. Check vacuum source and brake release vacuum lines for proper connections or slow leaks.

Fig. 93: Buick Riviera 1990 - Component Locations - Code B663: Circuit Diagram

Fig. 94: Buick Riviera 1990 - Component Locations - Code B663: Flow Chart Cruise Speed Difference Between Actual & Set Is Too Large

Buick Riviera 1990 - CODE B664, CRUISE - ACCELERATION TOO HIGH

This code will set and disengage the cruise control if vehicle acceleration exceeds a preset rate calibrated in the BCM. This could occur on slippery pavement or for some mechanical problems such as transmission slippage. Under these conditions, this code is normal. It should be cleared and vehicle operator should be advised of this.

Buick Riviera 1990 - CODE B667, SET/COAST OR RESUME/ACCEL CIRCUIT SHORTED

When cruise control ON/OFF switch is turned to the ON position and brake is released, system voltage is available at one side of normally open contacts on SET/COAST and RESUME/ACCEL switches. If SET/COAST or RESUME/ACCEL switches were stuck, or their signal wires to BCM were shorted to voltage, vehicle could begin cruise operation. In order to prevent this occurrence, Code B667 will set and disable cruise control, if signal voltage from SET/COAST circuit No. 84 or RESUME/ACCEL circuit No. 87, is high when cruise control ON/OFF switch is turned from OFF position to ON position or when ignition key is turned on and cruise control ON/OFF switch was left in the ON position. Cruise control will be disabled until BCM sees a low on both of these signals.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) BI76 and BI77 will display SET/COAST and RESUME/ACCEL switch status as HI or LO, depending on voltage state at BCM. If one of these inputs stays HI when switches are cycled, that particular switch or signal wire is shorted to voltage.

Test Number 2) This step checks if short circuit reading is due to switch or circuit.

Buick Riviera 1990 - Note on Intermittents

If an intermittent Code B667 is being set, manipulate related wiring while observing BI76 and BI77 displays. If failure is induced, reading will jump from LO to HI with the switch in the OFF position (not depressed). This code can also be set by vehicle operator if cruise ON/OFF switch is turned to the ON position, or the ON/OFF switch was left in the ON position when ignition is turned on and vehicle operator was depressing either the SET/COAST or RESUME/ACCEL switches.

Fig. 95: Buick Riviera 1990 - Component Locations - Code B667: Circuit Diagram

Fig. 96: Buick Riviera 1990 - Component Locations - Code B667: Flow Chart Set/Coast or Resume/Accel Circuit Shorted

Buick Riviera 1990 - CODE B671, CRUISE SERVO POSITION SENSOR CIRCUIT

Code B671 will set if ignition is on and the servo position sensor signal is less than 3 percent. During time failure is present cruise control will be disengaged.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) BD70 display indicates servo position. Normal range is greater than 3 percent.

Test Number 2) Check to see if fault is due to short or open in feedback circuits. Normal resistance across feedback coil should be 15-30 ohms.

Test Number 3) Checks to see if open circuit is due to servo or circuits.

Test Number 4) Checks to see if problem is intermittent. BD70 display will not go as low or high as BS05 display, because of its mechanical limits of travel. It should never go to less than 3 percent.

Buick Riviera 1990 - Note on Intermittents

If an intermittent Code B671 is being set, manipulate related wiring while observing BD70 display. If failure is induced, reading will jump from its normal value to a reading less than 3 percent.

Fig. 97: Buick Riviera 1990 - Component Locations - Code B671: Circuit Diagram

Fig. 98: Buick Riviera 1990 - Component Locations - Code B671: Flow Chart Cruise Servo Position Sensor Circuit

Buick Riviera 1990 - CODE B672, CRUISE VENT SOLENOID CIRCUIT PROBLEM

The cruise control vent solenoid receives pulsed voltage signals from BCM to control the amount of time solenoid is energized. While time output is HI, solenoid is energized and vacuum is not vented (or it is trapped) in servo. Code B672 will set if cruise is ON, brake is not depressed and BCM output is HI when it should be LO, or LO when it should be HI. Under either of these conditions, BCM will disable cruise control until it sees proper output signals. These determinations are made internal to BCM and may, or may not, affect HI or LO reading displayed during service mode. An output display of LO indicates circuit No. 403 should be de-energized (vent solenoid off) and an output display of HI indicates circuit No. 403 should be energized (vent solenoid on).

Circuit No. 403 will be HI when solenoid is energized as BCM is providing voltage to vent solenoid which has its own full time ground. Circuit No. 403 will be LO when the solenoid is de-energized as BCM removes voltage feed to solenoid.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) BO01 cycles vent solenoid. The HI and LO refer to commanded state of voltage at BCM.

Test Number 2) Checks to see if fault is due to servo or circuit.

Test Number 3) Checks to see if fault is due to open ground circuit or control circuit, including servo solenoid.

Test Number 4) Checks to see if fault is shorted servo or control circuit.

Buick Riviera 1990 - Note on Intermittents

If an intermittent Code B672 is being set, manipulate related wiring while in BO01 display and listen for solenoid to cycle (or stop cycling). This will have to be done slowly as this function cycles the solenoid on and off every 3 seconds. Ensure intermittent condition can be induced a few times during the on (or HI) output interval.

Fig. 99: Buick Riviera 1990 - Component Locations - Code B672: Circuit Diagram

Fig. 100: Buick Riviera 1990 - Component Locations - Code B672: Flow Chart Cruise Vent Solenoid Circuit Problem

Buick Riviera 1990 - CODE B673, CRUISE VACUUM SOLENOID CIRCUIT PROBLEM

The cruise control vent solenoid receives pulsed voltage signals from BCM to control the amount of time solenoid is energized. While time output is HI, solenoid is energized and vacuum is not vented (or it is trapped) in servo. Code B673 will set if cruise is ON, brake is not depressed and BCM output is HI. Under either of these conditions, BCM will disable cruise control until BCM sees proper output signals. These determinations are made internal to BCM and may or may not affect HI or LO reading displayed during service mode. An output display of LO indicates circuit No. 402 should be de-energized (vent solenoid off) and an output display of HI indicates circuit No. 402 should be energized (vent solenoid on).

Circuit No. 402 will be HI when solenoid is energized as BCM is providing voltage to vent solenoid which has its own full time ground. Circuit No. 402 will be LO when the solenoid is de-energized as the BCM removes voltage feed to solenoid.

NOTE:

Test numbers refer to numbers on diagnostic chart.

Test Number 1) BO02 cycles vacuum solenoid. The HI and LO refer to commanded state of voltage at BCM.

Test Number 2) Checks to see if fault is due to servo or circuit.

Test Number 3) Checks to see if fault is due to open ground circuit or control circuit, including servo solenoid.

Test Number 4) Checks to see if fault is shorted servo or control circuit. If vacuum solenoid is shorted (less than 25 ohms) BCM replacement will also be necessary.

Buick Riviera 1990 - Note on Intermittents

If an intermittent Code B673 is being set, manipulate related wiring while in BO02 display and listen for solenoid to cycle (or stop cycling). This will have to be done slowly as this function cycles the solenoid on and off every 3 seconds. Be aware that solenoid could be at end of 3 second interval. Ensure intermittent condition can be induced a few times during the on (or HI) output interval.

Fig. 101: Buick Riviera 1990 - Component Locations - Code B673: Circuit Diagram

Fig. 102: Buick Riviera 1990 - Component Locations - Code B673: Flow Chart Cruise Vacuum Solenoid Circuit Problem