GM Service Manual Online
For 1990-2009 cars only

Air Bag Indicator

The air bag indicator is a light emitting diode (LED) display that is located in the instrument cluster. The air bag indicator is operated by the inflatable restraint sensing diagnostic module (SDM) Module. The air bag indicator FLASHES 7 times when the ignition switch is turned to the RUN position. The SDM module sends a Class 2 serial data message to the instrument cluster to inform the instrument cluster when to turn ON the air bag indicator.

The air bag indicator will also turn ON when one of the following actions occurs:

    • The instrument cluster receives a Class 2 serial data message from the SDM module requesting the air bag indicator be turned ON.
    • The instrument cluster can not communicate with the SDM module using Class 2 serial data communications.
    • A diagnostic trouble code (DTC) is stored related to the system malfunction.

Refer to SIR in Restraints for more information about the air bag system.

Anti-Lock Indicator

The anti-lock indicator is a LED display that is located in the instrument cluster. The anti-lock indicator is operated by the electronic brake control module (EBCM) module. The instrument cluster turns ON the anti-lock indicator for 3 seconds when the ignition switch is turned to the RUN position. The EBCM module then sends a class 2 serial data message to the instrument cluster to turn OFF the anti-lock indicator as soon as the 3 second bulb check is complete.

The anti-lock indicator will also turn ON when one of the following actions occurs:

    • The instrument cluster receives a class 2 serial data message from the EBCM module requesting the anti-lock indicator be turned ON.
    • The instrument cluster can not communicate with the EBCM module using class 2 serial data communications.
    • A diagnostic trouble code (DTC) is stored related to the system malfunction.

The red brake indicator also turns ON for 3 seconds when the ignition switch is turned to the RUN position. Both the BCM and the EBCM can instruct the instrument cluster to turn ON the red brake indicator. The EBCM module will request the instrument cluster to turn the red brake indicator ON when one of the following actions occurs:

    • The EBCM module can not control the anti-lock indicator.
    • The instrument cluster receives a class 2 serial data message from the EBCM requesting that the red brake indicator be turned ON.

Refer to Anti-lock Brakes for more information about the anti-lock brake system.

Brake Indicator

The red brake warning indicator is a LED display that is located in the instrument cluster. The red brake warning indicator is operated by the EBCM module and by the BCM. The red brake warning indicator is used to indicate when a brake system failure occurs or when the parking brake is set.

The red brake warning indicator turns ON when one of the following actions occurs:

    • A low brake pressure condition exists in the brake system.
    • A low brake fluid condition exists in the brake system.
    • The EBCM module can not control the anti-lock indicator.
    • The pressure differential switch is closed.
    •  The BCM sends a class 2 serial data message to the instrument cluster to turn ON the red park brake indicator to indicate that the park brake is set.
    • The instrument cluster receives a class 2 serial data message from the EBCM module requesting that the red brake indicator be turned ON.

Refer to Hydraulic Brakes for more information about the base brake system.

Battery Indicator

The battery indicator is a LED display that is located in the instrument cluster. The VCM/PCM sends a class 2 serial data message to the instrument cluster in order to instruct the instrument cluster when to turn ON or when to turn OFF the battery indicator. When the ignition switch is turned from the OFF position to the UNLOCK position the battery indicator will turn ON. The battery indicator will remain ON while the ignition switch is moved from UNLOCK position to RUN position. The battery indicator will remain ON until the ignition switch is turned to the CRANK position and back to the RUN position. Once the ignition switch is RELEASED to the RUN position after it was just in the CRANK position the instrument cluster will turn the battery indicator ON for 3 seconds. The instrument cluster will then respond to the last Class 2 serial data message received from the VCM/PCM. The VCM/PCM will order the instrument cluster to turn the battery indicator OFF if the generator is charging. A diagnostic trouble code (DTC) will be stored in the VCM/PCM related to the system malfunction. Refer to Engine Electrical for more information about the battery indicator.

Check Gauges Indicator

The check gauges indicator is a LED display located in the instrument cluster. The check gauges indicator turns ON for 3 seconds when the ignition switch is turned to the RUN position. The instrument cluster is constantly monitoring the engine coolant temperature and engine oil pressure when the engine s running. The engine coolant temperature information is sent to the instrument cluster over the Class 2 serial data line by the VCM/PCM. The engine oil pressure information is sent to the instrument cluster from a designated circuit connected to the oil pressure sensor. The instrument cluster will turn the CHECK GAUGES indicator ON if the engine coolant temperature gets too high or if the engine oil pressure gets too low while the engine is running.

Gate Ajar Indicator (Utility Only)

The gate ajar indicator display is a LED display that is located in the instrument cluster. The gate ajar indicator turns ON when the instrument cluster receives a Class 2 serial data message from the body control module (BCM) requesting that the gate ajar indicator be turned ON. Refer to Body Rear End for more information about the gate ajar indicator.

High Beam Indicator

The high beam indicator is a replaceable lamp that is located in the instrument cluster. The BCM sends a class 2 serial data message to the instrument cluster to instruct the instrument cluster when to turn ON or when to turn OFF the high beam indicator. If the BCM detects that the high beams are ON it will instruct the instrument cluster to turn ON the high beam indicator. Refer to Lighting Systems for more information about the high beam indicator.

Low Fuel Indicator

The low fuel indicator is a LED display is that is located in the instrument cluster. The low fuel indicator will turn ON for 3 seconds when the ignition switch is turned to the RUN position. When the ignition switch is in the RUN position, the VCM/PCM constantly sends a Percent of Fuel Remaining message over the class 2 serial data line to the instrument cluster in order to display the appropriate fuel level. The instrument cluster uses the fuel level information from the PCM/VCM in order to operate the fuel gauge. The information is also used in order to determine when the low fuel indicator should be turned ON.

Overspeed Indicator (Export Only)

The overspeed indicator is a LED display that is located in the instrument cluster. The BCM sends a class 2 serial data message to the instrument cluster in order to inform the instrument cluster when to turn ON the overspeed indicator. The overspeed indicator will turn ON for 3 seconds when one of the following actions occurs:

    • The ignition switch is turned to the RUN position.
    • The indicator is commanded ON by the BCM.

Refer to Audible Warnings for more information on the overspeed alarm system.

Service 4WD Indicator

The service 4WD indicator is a LED display located in the instrument cluster. The Automatic Transfer Case (ATC) module sends a class 2 serial data message to the instrument cluster to instruct the instrument cluster when to turn ON the service 4WD indicator.

The service 4WD indicator will also turn ON when one of the following actions occurs:

    • The instrument cluster receives a class 2 serial data message from the ATC module requesting the service 4WD indicator be turned ON.
    • The instrument cluster can not communicate with the ATC module using class 2 serial data communications.
    • A diagnostic trouble code (DTC) is stored related to the system malfunction.

Seat Belt Indicator

The seat belt indicator is a LED display located in the instrument cluster. The BCM sends a class 2 serial data message to the instrument cluster in order to inform the instrument cluster when to turn ON the seat belt indicator. The seat belt system has an enhanced seat belt warning system. The system activates the following components when the ignition has been turned to the RUN position and the driver's seat belt has not been buckled:

    • The warning lamp for about 75 seconds
    • The audible warning for 8 seconds

The seat belt warning lamp will be ON constant for the first 20 seconds and will FLASH for the remaining 55 seconds. The audible warning will stay ON when the driver seat belt is not fastened during the 8 second time period. The sequence of operation of the warning lamp and audible warning follows:

The Driver Seat Belt Is Unbuckled.

  1. Turn the ignition switch to the RUN position.
  2. The seat belt indicator turns ON constantly for 20 seconds.
  3. The seat belt audible warning turns ON and stays ON for 8 seconds, then turns OFF.

  4. The seat belt indicator FLASHES for the remaining 55 seconds.
  5. If the driver seat belt buckle is buckled before the 8 second period is over, the audible warning and the seat belt indicator will turn OFF.

The Driver Seat Belt Is Buckled.

  1. Turn the ignition switch to the RUN position.
  2. The seat belt indicator turns ON for 75 seconds.
  3. The seat belt audible warning will not turn ON.

  4. The seat belt indicator turns OFF after 75 seconds.
  5. If the driver seat belt buckle is unbuckled during the first 8 seconds, the seat belt audible warning will turn ON for the remainder of the 8 second delay.
  6. Refer to Seat Belts or Audible Warnings for more information about the seat belt system.

Security Indicator

The security indicator is a LED display that is located in the instrument cluster. The BCM sends a class 2 serial data message to the instrument cluster in order to inform the instrument cluster when to turn ON or FLASH the security indicator. If the security indicator is ON a DTC will be stored related to the system malfunction. Refer to Theft Deterrent for more information on the security system.

Service Engine Soon -- Malfunction Indicator Lamp (MIL)

The service engine soon indicator, or the malfunction indicator lamp (MIL), is a LED display located in the instrument cluster. The service engine soon indicator is controlled directly by the VCM/PCM. The service engine soon indicator should turn ON when the ignition switch is in the RUN position and the engine is OFF. The service engine soon indicator should turn OFF 1-5 seconds after the engine starts. Service to the emission control system or service to the engine control system may be required if the service engine soon indicator stays ON or turns ON while driving. If the service engine soon indicator is ON with the engine running a DTC will be stored related to the system malfunction. Refer to Engine Controls for more information about the SERVICE ENGINE SOON indicator.

Turn Signal Indicators

The turn signal indicator is a replaceable lamp that is located in the instrument cluster. The turn signal indicators are directly operated by the turn signal switch and the turn signal flasher. The turn signal indicators do not turn ON during the bulb check or when the ignition switch is in the run position. Refer to Lighting Systems for more information about the turn signals.

Up-Shift Indicator (Manual Transmission Only)

The up-shift indicator is a LED display that is located in the instrument cluster. The up-shift indicator turns ON when the instrument cluster receives a class 2 serial data message from the VCM/PCM that requests the instrument cluster to turn the up-shift indicator ON. The up-shift indicator located on the instrument cluster turns ON in order to indicate the optimum shift points for maximum fuel economy. Shift the transmission to the next higher gear range, if the conditions permit, when the lamp turns ON. Control of the up-shift indicator is a function of the PCM/VCM. The following conditions are monitored:

    • The engine speed
    • The load
    • The throttle position

These conditions determine if the PCM/VCM will turn the up-shift indicator ON. If the up-shift indicator is erratic or inoperative, verify the integrity of the circuit. Refer to Manual Transmission or Engine Controls for more information about the up-shift indicator.

PRNDL Indicator (Park Reverse Neutral Drive Low)

The PRNDL display is a class 2 serial data message to the instrument cluster from the PCM/VCM. The PRNDL display is a vacuum florescent (VF) display which displays the fixed gear position of P, R, N, D, 3, 2, 1 surrounded by a moveable square flag in order to indicate the selected gear position. The position of the moveable square flag is sent to the instrument cluster from the transmission range switch over the class 2 serial data line. The transmission range switch and the neutral safety back up (NSBU) switch operate separately but are incorporated into one part. If the vehicle is equipped with a column shift steering column it will also have a park position switch. The park position switch (if equipped) must also be CLOSED in order for the instrument cluster to display the PARK position. Since the system is entirely electronic, there is not any internal adjustment. The PRNDL display will operate as follows:

    • The PRNDL display will display the PARK position when a class 2 serial data message is received from the PCM/VCM indicating the transmission is in the PARK position and for vehicles which have a column shift on the steering column, the park position switch must also be CLOSED (low input).
    • The PRNDL display will display a gear position if a class 2 serial data message from the PCM/VCM is received indicating the gear position of the transmission.
    • The moveable square flag will not appear on the instrument cluster in order to show no gear was selected when the instrument cluster does not receive a class 2 serial data message from the PCM/VCM within 5 seconds of entering the UNLOCK or the RUN position.

Refer to Engine Controls or Transmission/Transaxle for more information about the PRNDL indicator.

Park Switch (Column Shift Only)

The park position switch is only used on vehicles which have a gear shift lever on the column. The park position switch is part of the linear shift assembly in the steering column. The scan tool can display the state of the park switch.

OPEN is displayed when the gear shift lever is not in PARK.

CLOSED is displayed when the following conditions exist:

    • The gear shift lever is in the PARK position
    • The gear shift lever is at the normal rest position
    • The park position switch is providing a ground to the instrument cluster for the park switch input

Refer to Steering Wheel and Column for more information on the park switch.

Bulb Check

The purpose of illuminating the instrument cluster PRNDL display and indicator displays during the power up of the instrument cluster is to verify that all segments of the PRNDL display and that all of the indicator displays are working properly. The turn signal indicators do not turn ON during the bulb check. If an expected indicator or PRNDL segment does not function properly during the bulb check further diagnosis of the instrument cluster may be necessary. Refer to Diagnostic System Check - Instrument Cluster .