GM Service Manual Online
For 1990-2009 cars only

The instrument cluster scan tool data display values and definition information can assist in diagnosing instrument cluster related problems, especially when no diagnostic trouble codes (DTC) are stored in memory. A vehicle scan tool data can be compared with the data display values from a known good vehicle in the scan tool data display table. When data from the vehicle differs from the typical data display value, the data definition information will help in understanding the nature of the difference and the source of the problem.

Data

Battery Voltage -- Range: 9.0 - 19.0 Volts: This data refers to the battery system voltage as measured by the instrument cluster (IPC).

Vehicle Speed -- Range: 0 MPH - 120 MPH (0 KM/H - 193 KM/H): This is the cluster measurement of the vehicle's speed from a discrete input from the vehicle control module (VCM).

Monitored Coolant Temperature - Range: -40°F-419°F (-40°C- 215°C): This data is the clusters measurement of the engine coolant temperature as provided by the VCM on the class 2 serial data line. If a class 2 communication failure occurs, this data will be -40°.

Monitored Fuel Level - Range: 0 - 100 percent: This data is the cluster's measurement of the fuel tank level as provided by the VCM on the class 2 serial data line. If a class 2 communication failure occurs, this data will be 0.

Displayed Odometer - Range: 0 Miles - 999,999 Miles/Kilometers: This data refers to the displayed odometer mileage on the odometer display.

Displayed Trip Odometer - Range: 0 Miles - 9,999.9 Miles/Kilometers: This data refers to the displayed trip odometer mileage displayed on the trip odometer display.

Inputs

PRNDL State - Range: Park / Reverse / Neutral / Drive / Third / Second / First / Invalid: This data input refers to the PRNDL position data that is communicated to the cluster over the class 2 serial data line by the VCM. The value of this parameter corresponds to the gear that is selected on the PRNDL display. The value of this parameter will be INVALID under the following conditions:

    • The data from the VCM is INVALID.
    • The data from the VCM is PARK but the cluster does recognize the class 2 message from the VCM.
    •  A class 2 communication failure has occurred.

When the value of this parameter is INVALID, no gear will be shown as selected on the PRNDL display.

Dimming - Range: Active / Inactive: This data refers to the dimming availability feature of the PRNDL and odometer/trip odometer vacuum florescent displays. ACTIVE is displayed when the PRNDL and odometer/trip odometer vacuum florescent displays can be dimmed using the dimming thumbwheel switch. INACTIVE is displayed when the PRNDL and the odometer/trip odometer vacuum florescent displays cannot be dimmed using the dimming thumbwheel displays.

Park Switch - Range: Open / Closed: This data input refers to the state of the gear shift park position switch. OPEN is displayed when the gear shift is not fully seated in park. CLOSED is displayed when the gear shift is in the park position and the gearshift lever is at the normal rest position.

Trip Reset Switch - Range: Active / Inactive: This data refers to the position of the trip odometer reset switch. ACTIVE is displayed when the trip reset switch is pushed in. INACTIVE is displayed when the trip reset switch is in the normal position (not pushed in).

Outputs

Low Fuel Lamp - Range: ON / OFF: This output refers to the commanded state of the LOW FUEL indicator located in the instrument cluster. ON is displayed when the instrument cluster is commanding the LOW FUEL indicator ON. OFF is displayed when the instrument cluster is not commanding the LOW FUEL indicator ON. The instrument cluster will command the LOW FUEL indicator ON under the following conditions:

    • When the instrument cluster receives a class 2 (percent monitored fuel level) message of less than 18 percent from the VCM. Once the lamp is ON, the Monitored Fuel Level must rise above 22 percent in order to turn the lamp OFF.
    • A class 2 communication failure has occurred.
Service AWD - Range: ON / OFF: This output refers to the commanded state of the All Wheel Drive (AWD) lamp illumination by the instrument cluster. ON is displayed when the instrument cluster is commanding the Service AWD lamp to be illuminated. OFF is displayed when the instrument cluster is not commanding the Service AWD lamp to be illuminated. The instrument cluster will illuminate the Service AWD lamp when it receives a class 2 serial data message from the Automatic Transfer Case (ATC) Module indicating an AWD malfunction.

Anti-Lock Brake System (ABS) Lamp - Range: ON / OFF: This output refers to the commanded state of the ABS lamp illumination by the instrument cluster. ON is displayed when the instrument cluster is commanding the ABS lamp to be illuminated. OFF is displayed when the instrument cluster is not commanding the ABS lamp to be illuminated. The instrument cluster will command the ABS lamp to be illuminated under the following conditions:

    • When the instrument cluster receives a class 2 message from the electronic brake control module (EBCM) indicating there is a malfunction in the ABS system
    • During the bulb check period for 3 seconds after the ignition switch is first turned to RUN.
    • A class 2 communication failure occurs.
Brake Lamp - Range: ON / OFF: This output refers to the commanded state of the BRAKE lamp illumination by the instrument cluster. ON is displayed when the instrument cluster is commanding the BRAKE lamp to be illuminated. OFF is displayed when the instrument cluster is not commanding the BRAKE lamp to be illuminated. The instrument cluster will command the BRAKE lamp to be illuminated under the following conditions:

    • The BRAKE lamp will flash when the instrument cluster receives a class 2 message from the body control module (BCM) that the parking brake is set.
    •  When the instrument cluster receives a class 2 message from the electronic brake control module (EBCM) that there is a problem with the base brake system (non-ABS portion).
    • During the bulb check period for 3 seconds after the ignition switch is first turned to the RUN position.
Fasten Seat Belts - Range: ON / OFF: This output refers to the commanded state of the fasten seat belts lamp illumination by the instrument cluster. ON is displayed when the instrument cluster is commanding the fasten seat belts lamp to be illuminated. OFF is displayed when the instrument cluster is not commanding the fasten seat belts lamp to be illuminated. The instrument cluster will command the fasten seat belts lamp to be illuminated under the following conditions:

    • The fasten seat belt lamp will illuminate for 20 seconds followed by 55 seconds of flashing when it receives a class 2 message from the body control module (BCM) that the drivers seat belt is not buckled.
    • During the bulb check period for about 3 seconds after the ignition switch is first turned to the RUN position providing the drivers seat belt is not buckled. If the seat belt is buckled when the ignition switch is turned to the RUN position, the seat belt indicator will remain OFF.
    • If a class 2 communication failure occurs, the fasten seat belt lamp will illuminate for 20 seconds followed by 55 seconds of flashing.
Security Lamp - Range: ON / OFF: This output refers to the commanded state of the SECURITY indicator located on the instrument cluster. ON is displayed when the instrument cluster is commanding the SECURITY indicator ON. OFF is displayed when the instrument cluster is not commanding the SECURITY indicator ON. The instrument cluster will command the SECURITY indicator to be displayed in the under the following conditions:

    • When the instrument cluster receives a class 2 serial data message from the (BCM).
    • A class 2 communication failure occurs and the ignition switch in the RUN position.
High Beam Lamp - Range: ON / OFF: This output refers to the commanded state of the high beam lamp illumination by the instrument cluster . ON is displayed when the instrument cluster is commanding the high beam lamp to be illuminated. OFF is displayed when the instrument cluster is not commanding the high beam lamp to be illuminated. The instrument cluster will illuminate the high beam lamp when the instrument cluster receives a class 2 serial data message from the body control module (BCM).

Battery - Range: ON / OFF: This output refers to the commanded state of the battery (voltage) icon indicator on the instrument cluster. ON is displayed when the instrument cluster is commanding the battery indicator ON. OFF is displayed when the instrument cluster is not commanding the battery indicator ON. The instrument cluster will command the battery indicator ON under the following conditions:

    • The instrument cluster receives a class 2 message from the VCM indicating that there is a charging system problem.
    • The ignition switch is turned to UNLOCK or RUN without the engine running.
    • A class 2 communication failure occurs.
    • During a 3 second bulb check after the engine has been started.
TOW/HAUL Lamp - Range: ON / OFF: This output refers to the commanded state of the TOW/HAUL indicator located on the instrument cluster. ON is displayed when the instrument cluster is commanding the TOW/HAUL indicator ON. OFF is displayed when the instrument cluster is not commanding the TOW/HAUL ON. The indicator will be ON when the TOW/HAUL switch is pressed and the body control module (BCM) sends a class 2 serial data message to the instrument cluster.

Air Bag Lamp - Range: ON / OFF: This output refers to the commanded state of the Air Bag lamp illumination by the Inflatable Restraint Sensing & Diagnostic Module (SDM). The Air Bag lamp is controlled by a class 2 message from the SDM. ON is displayed when the SDM commands the indicator ON. ON is displayed when the SDM does not command the indicator ON.

Overspeed - Range: ON / OFF: This output refers to the commanded state of the Overspeed telltale located in the instrument cluster. ON is displayed when the instrument cluster is commanding the Overspeed telltale ON. OFF is displayed when the instrument cluster is not commanding the Overspeed telltale ON. The instrument cluster will display the Overspeed telltale when the instrument cluster receives a class 2 serial data message from the BCM.