GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2008 🢒 Corvette 🢒 Power and Signal Distribution 🢒 Wiring Systems and Power Management 🢒 DTC B0976, B0977, or B0978

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC B0976 01 : Power Mode OFF Indicator Control Circuit Short to Battery

DTC B0976 06 : Power Mode OFF Indicator Control Circuit Short to Ground or Open

DTC B0977 01 : Power Mode START Indicator Control Circuit Short to Battery

DTC B0977 06 : Power Mode START Indicator Control Circuit Short to Ground or Open

DTC B0978 01 : Power Mode ACCESSORY Indicator Control Circuit Short to Battery

DTC B0978 06 : Power Mode ACCESSORY Indicator Control Circuit Short to Ground or Open

Circuit/System Description

The ignition mode switch has 3 LEDs that indicate the vehicle power mode. When the vehicle is in the Off mode, the Off LED may illuminate. Pressing the lower button of the ignition mode switch, the vehicle enters the accessory mode and ACC LED will illuminate. Keeping the lower button pressed for about 5-6 seconds, the vehicle enters run mode with the engine off and the START LED will illuminate. All these LED’s have the voltage supplied from the body control module (BCM) through the ignition mode switch supply voltage circuit. The ground path for each LED is controlled by the BCM.

Conditions for Running the DTC

Voltage supplied to the module is in the normal operating voltage range of 9-16 V.

Conditions for Setting the DTC

B0976 01

    • The BCM detects a short to battery in the off indicator control circuit.
    • The above condition exists for more than 5 seconds.

B0977-B0978 01

    • The BCM detects a short to battery in the respective indicator control circuit, when the output is active.
    • The above condition exists for more than 1 second.

B0976-B0978 06

    • The BCM detects an open or short to ground in the respective indicator control circuit, when the output is inactive.
    • The above condition exists for more than 1 second.

Action Taken When the DTC Sets

The BCM disables the respective output until the next ignition cycle.

Conditions for Clearing the DTC
    • A current DTC clears when the malfunction is no longer present.
    • A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Reference Information

Schematic Reference

Power Moding Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

    •  Retained Accessory Power Description and Operation
    •  Power Mode Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Ignition ON, run the mode switch LED test with a scan tool. Observe the operation of the ignition mode LEDs. The LEDs should illuminate simultaneously within 5 seconds.

Circuit/System Testing
  1. Ignition OFF, disconnect the harness connector at the ignition mode switch.
  2. Ignition ON, verify a test lamp illuminates between the B+ circuit and ground.
    3. ⇒If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  3. Connect a test lamp between the control circuit terminal H and the B+ circuit terminal G.
  4. Perform the Mode switch LED test with a scan tool. The test lamp should illuminate.
    5. ⇒If the test lamp is always ON, test the control circuit for a short to ground. If all circuits test normal, replace the BCM.
    ⇒If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If all circuits test normal, replace the BCM.
  5. Connect a test lamp between the control circuit terminal J and the B+ circuit terminal G.
  6. Perform the Mode switch LED test with a scan tool. The test lamp should illuminate.
    7. ⇒If the test lamp is always ON, test the control circuit for a short to ground. If all circuits test normal, replace the BCM.
    ⇒If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If all circuits test normal, replace the BCM.
  7. Connect a test lamp between the control circuit terminal B and the B+ circuit terminal G.
  8. Perform the Mode switch LED test with a scan tool. The test lamp should illuminate.
    9. ⇒If the test lamp is always ON, test the control circuit for a short to ground. If all circuits test normal, replace the BCM.
    ⇒If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If all circuits test normal, replace the BCM.
  9. If all circuits test normal, replace the ignition mode switch.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References