Interior Backlighting Malfunction

Interior Backlighting Malfunction

Diagnostic Instructions

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

Circuit/System Description

When the ignition switch is turned to the RUN position, the radio's VF displays turn ON at maximum brightness. When the park lamps are ON, all incandescent back lighting turn ON at the dimming level indicated by the instrument panel (I/P) dimmer switch. At the same time all VF displays dim to match the indicated dimming level. The panel dimmer switch potentiometer is an input to the body control module (BCM). When the driver selects a dimming setting by moving the I/P dimming switch potentiometer, all incandescent back lighting lamps are provided with a specific voltage. The incandescent back lighting lamps are then grounded at G201, G302, and G303. When the I/P dimmer switch is moved from MIN to MAX, all vacuum fluorescent (VF) displays, as well as all incandescent back lighting respond from minimum intensity to maximum brightness in response to the I/P dimmer switch.

Circuit/System Verification

Ignition ON, observe the scan tool Dimming Input parameter while operating the dimmer switch from high to low. The voltage reading should change from high to low as the switch is rotated.

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

If the scan tool dimmer control operates normal, refer to Interior Backlighting Circuit Test.

Circuit/System Testing

Dimmer Switch Circuit Test

1. Ignition OFF, disconnect the headlamp switch connector X1.
2. Test for less than 1 ohm of resistance between the low reference circuit terminal X1 H and ground.

^ If greater than the specified range, test the low reference circuit for an open/high resistance.

3. Ignition ON, verify that the scan tool dimming input parameter displays less than 1.0 volt.

^ If the parameter displays greater than the specified value, test the switch signal circuit terminal X1 G for a short to voltage. If the circuit tests normal replace the BCM.

4. Install a 3A fused jumper wire between the signal circuit terminal X1 G and the 5.0 volt reference circuit terminal X1 A. Verify the scan tool dimming input parameter displays greater than 4.0 volts.

^ If the parameter displays less than the specified value, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

5. If the circuits test normal test or replace the headlamp switch.

Interior Backlighting Circuit Test

1. Ignition OFF, disconnect the harness connector at the affected component.
2. Ignition OFF, verify that a test lamp illuminates between the listed ground circuit terminal and battery voltage.

* Garage door opener terminal 3
* Sunroof switch terminal C
* Auxiliary HVAC control module (CJ3) terminal 7
* Auxiliary HVAC control module (CJ2) terminal A4
* Transfer case shift control switch terminal D
* IPC terminal A5
* HVAC control module terminal X1 B9
* Rear window wiper/washer switch terminal B
* Headlamp switch terminal X1 C
* Upper right SWC switch terminal 5
* Upper left SWC switch terminal 3
* Lower left SWC switch terminal 4
* Lower right SWC switch terminal 4

^ If the test lamp does not illuminate, test the ground circuit for an open/high resistance.

3. Connect a test lamp between the listed backlighting control circuit terminal and ground.

* Garage door opener terminal 2
* Sunroof switch terminal B
* Auxiliary HVAC control module (CJ3) terminal 8
* Auxiliary HVAC control module (CJ2) terminal A5
* Transfer case shift control switch terminal C
* IPC terminal A7
* HVAC control module terminal X1 A7
* Rear window wiper/washer switch terminal C
* Headlamp switch terminal X1 CB
* Upper right SWC switch terminal 3
* Upper left SWC switch terminal 2
* Lower left SWC switch terminal 1
* Lower right SWC switch terminal 1

4. Command the dimming test high to low with a scan tool. The test lamp should turn from bright to dim when changing between the commanded states.

^ If the test lamp is always off, test the control circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the BCM.

^ If the test lamp is always bright, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.

5. If all circuits test normal, test or replace the affected component.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

* Steering Wheel Control Switch Assembly Replacement
* Rear Window Wiper and Washer Switch Replacement
* Transfer Case Shift Control Switch Replacement (GMC, Buick)
* Headlamp Switch Replacement