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. For more detailed information concerning interior lamp operation refer to Interior Lighting Systems Description and Operation .

Schematic Reference

Interior Lights Dimming Schematics

Connector End View Reference

Lighting Systems Connector End Views

Electrical Information Reference

Scan Tool Reference

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.

Dimmer Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the I/P Dimmer switch.
2. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit terminal 10.

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

3. Ignition ON, verify the scan tool dimming control signal parameter is less than 0.0 volts.

⇒	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.

4. Ignition ON, test for B+ between the voltage reference circuit terminal 5 and ground.

⇒	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.

5. 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.

⇒	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.

6. If all circuits test normal, test or replace the I/P 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.

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

3. Connect a test lamp between the I/P lamps dimmer switch signal circuit and ground.
4. 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.

⇒	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, test or replace the component with the inoperative incandescent backlighting.

Interior Backlighting Malfunction - LED

1. Ignition OFF, disconnect the C3 harness connector at the BCM.
2. Ignition ON, verify that a test lamp illuminates between the BCM 2 fuse voltage supply circuit terminal 2 and ground.

⇒	If the test lamp does not illuminate, test the voltage supply circuit for a short to ground or an open/high resistance.

3. Ignition OFF, reconnect the C3 harness connector at the BCM.
4. Ignition OFF, disconnect the harness connector at the component with the inoperative LED backlighting.
5. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit.

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

6. Connect a test lamp between the dimming control circuit and ground.
7. 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.

⇒	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.

8. 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 C3 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.

⇒	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.

4. If all circuits test normal, replace the HVAC control module.

Front Door Switch Indicator Malfunction

1. 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.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.