GM Service Manual Online
For 1990-2009 cars only

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.

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Body Control Module (BCM) 1 Fuse B+

B1395 03

B1395 03

--

--

Body Control Module (BCM) 2 Fuse B+

3

3

--

--

Body Control Module (BCM) 7 Fuse B+

B2652 00

B2652 00

--

--

I/P Dimming Voltage Reference

B1395 03

B2652 00

B1395 07

--

I/P Dimmer Switch Signal

B1395 03

1

1

--

I/P Lamps Dimmer Switch Control

B2652 00

2

2

--

Indicator Dimming Control

B2625 00

4

4

--

LED Backlight Dimming Control

B2610 00

3

3

--

I/P Dimmer Switch Low Reference

--

1

--

--

I/P Dimmer Switch Ground

--

1

--

--

1. Dimmer Switch Malfunction

2. Interior Backlighting Malfunction -- Incandescent

3. Interior Backlighting Malfunction -- LED

4. HVAC Fan Speed/Rear Window Defogger Indicator Malfunction

Circuit/System Description

The instrument panel (I/P) dimmer switch is used to increase and decrease the brightness of the interior backlighting components. The I/P dimmer switch provides a voltage signal that will increase as the brightness of the light are increased and decrease as the brightness of the lights are decreased. The body control module (BCM) provides a low reference signal and a B+ voltage reference to the I/P dimmer switch. When the I/P dimmer switch is placed in the desired position, the dimmed voltage setting is applied from the I/P dimmer switch through the I/P dimmer switch signal circuit to the BCM. The BCM interprets the signal and applies the dimmed voltage to the I/P lamps supply voltage circuit and the interior backlighting components dim to the requested level.

Reference Information

Schematic Reference

Interior Lights Dimming Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Interior Lighting Systems 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, observe the scan tool Dimming Control Signal parameter while operating the dimmer switch from high to low. The reading should change from a high percent to a low percent as the switch is activated.

If the reading does not change, refer to Dimmer Switch Malfunction.

Circuit/System Testing

Dimmer Switch Malfunction

  1. Ignition OFF, disconnect the harness connector at the dimmer switch.
  2. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit terminal 10.
  3. If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  4. Ignition ON, verify the scan tool Dimming Control Signal parameter is less than 0.0 volts.
  5. If greater than the specified range, test the signal circuit terminal 9 for a short to voltage. If the circuit tests normal, replace the BCM.
  6. Ignition ON, test for B+ between the voltage reference circuit terminal 5 and ground.
  7. If less than the specified range, test the voltage reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
    If greater than the specified range, test the voltage reference circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  8. Install a 3A fused jumper wire between the signal circuit terminal 9 and the B+ reference circuit terminal 5. Verify the scan tool Dimming Control Signal parameter is greater than 2.5 volts.
  9. If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  10. If all circuits test normal, test or replace the dimmer switch.

Interior Backlighting Malfunction - Incandescent

  1. Ignition OFF, disconnect the harness connector at the component with the inoperative incandescent backlighting.
  2. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit.
  3. If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  4. Connect a test lamp between the dimming control circuit and ground.
  5. Command the Incandescent Dimming Control ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
  6. If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM
    If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  7. If all circuits test normal, test or replace the component with the inoperative incandescent backlighting.

Interior Backlighting Malfunction - LED

  1. Ignition OFF, disconnect the X3 harness connector at the BCM.
  2. Ignition ON, verify that a test lamp illuminates between the BCM 2 fuse B+ circuit terminal 2 and ground.
  3. If the test lamp does not illuminate, test the voltage supply circuit for a short to ground or an open/high resistance.
  4. Ignition OFF, connect the X3 harness connector at the BCM.
  5. Disconnect the harness connector at the component with the inoperative LED backlighting.
  6. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit.
  7. If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  8. Connect a test lamp between the dimming control circuit and ground.
  9. Command the LED Dimming Control ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
  10. If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
    If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  11. If all circuits test normal, test or replace the component with the inoperative LED backlighting.

HVAC Fan Speed/Rear Window Defogger Indicator Malfunction

  1. Ignition OFF, disconnect the X3 harness connector at the HVAC control module.
  2. Connect a test lamp between the control circuit terminal 1 and ground.
  3. Command the LED Dimming Control ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
  4. If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
    If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  5. If all circuits test normal, replace the HVAC control module.

Front Door Switch Indicator Malfunction

Ignition ON, with a scan tool command the inoperative front door switch Integrated Sw. Backlighting Test ON and OFF with a scan tool. The switch backlighting should turn On and Off when changing between the commanded states.

If the switch backlighting does not turn On and Off or remains ON at all times, replace the inoperative driver door switch.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Electronic Traction Control Switch Replacement
    •  Radio Replacement
    •  Driver Information Display Switch Replacement
    •  Hazard Warning Switch Replacement
    •  Instrument Panel Lamp Dimmer Switch Replacement
    •  Transmission Floor Shift Control Indicator Lamp Replacement
    •  Sunroof Switch Replacement
    •  Steering Wheel Replacement
    •  Rear Window Wiper and Washer Switch Replacement
    •  Clock Replacement
    •  Automatic Transmission Control Indicator Replacement
    •  Steering Wheel Control Switch Assembly Replacement
    •  Control Module References for BCM, DDM, HVAC, IPC, or PDM replacement, setup, and programming