The body control module (BCM) supplies a voltage reference through the I/P dimming voltage reference circuit to the interior lamp dimmer switch, which is part of the interior lamp switch. When the dimmer switch is placed in a desired brightness position, reference voltage is applied through the dimmer switch rheostat and the I/P dimming signal circuit to the BCM. The BCM interprets this voltage signal, then applies a pulse width modulated (PWM) voltage through the instrument panel lamp supply voltage circuit to the lamps. At the same time the BCM sends a serial data message requesting the front door modules to illuminate the door switches.

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

Scan Tool Reference

Control Module References for Scan Tool Information

1. Ignition ON, observe the I/P dimming lamps while commanding the Incandescent Dimming ON and OFF with a scan tool. The I/P dimming lamps should turn ON and OFF when changing between the commanded states.

⇒	If any of the lamps do not turn ON and OFF when commanded, refer to I/P Dimming Lamps Circuit Test.

2. Observe the I/P dimming lamps while operating the dimmer switch from high to low. The lamps should smoothly vary in brightness as the switch is rotated.

⇒	If the lamps do not smoothly vary in brightness as the switch is rotated, refer to Dimmer Switch Circuit Test.

I/P Dimming Lamps Circuit Test

1. Ignition OFF, disconnect the harness connector at the appropriate component.
2. Test for less than 10 ohms between the ground circuit terminal listed below and ground:

•	Instrument Panel Cluster (IPC) - Terminal 1

•	Driver Information Center (DIC) - Terminal 4

•	PRNDL Lamp (Console Shift) - Terminal B

•	HVAC Control Module (CJ2) - X1 Terminal A6

•	HVAC Control Module (C67) - X1 Terminal B6

•	Radio - X1 Terminal B5

•	Headlamp Switch - Terminal 13

•	Driver Window Switch - X2 Terminal B

•	Driver Door Lock Switch - Terminal B

•	Passenger Window Switch - Terminal C

•	Passenger Door Lock Switch - Terminal B

•	Outside Rearview Mirror Switch - Terminal B

•	Right Steering Wheel Control (UK3) - Terminal 1

•	Left Steering Wheel Control (UK3) - Terminal 8

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

3. Connect a test lamp between the appropriate signal circuit terminal and ground:

•	Instrument Panel Cluster (IPC) - Terminal 13

•	Driver Information Center (DIC) - Terminal 1

•	PRNDL Lamp (Console Shift) - Terminal A

•	HVAC Control Module (CJ2) - X1 Terminal A5

•	HVAC Control Module (C67) - X1 Terminal B5

•	Radio - X1 Terminal B4

•	Headlamp Switch - Terminal 14

•	Driver Window Switch - X1 Terminal F

•	Driver Door Lock Switch - Terminal A

•	Passenger Window Switch - Terminal B

•	Passenger Door Lock Switch - Terminal A

•	Outside Rearview Mirror Switch - Terminal E

•	Right Steering Wheel Control (UK3) - Terminal 2

•	Left Steering Wheel Control (UK3) - Terminal 6

4. Ignition ON, command the Incandescent Dimming 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 signal 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 signal 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.

Dimmer Switch Circuit Test

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Ignition OFF, test for less than 10 ohms between the low reference circuit terminal 1 and ground.

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

3. Ignition ON, test for 9.8-10.2 volts between the 10-volt reference circuit terminal 10 and ground.

⇒	If greater than the specified range, test the 10-volt reference circuit for a short to voltage. If the circuit tests normal, replace the BCM.

⇒	If less than the specified range, test the 10-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

4. Verify the I/P dimming lamps are at their lowest intensity.

⇒	If the I/P dimming lamps are not at their lowest intensity, test the signal circuit terminal 9 for a short to voltage.

5. Install a 3A fused jumper wire between the signal circuit terminal 9 and the voltage reference circuit terminal 10. Verify the I/P dimming lamps are at their highest intensity.

⇒	If the I/P dimming lamps are not at their highest intensity, test the signal circuit for a short to ground or an open/high resistance.

6. If all circuits test normal, test or replace the headlamp switch.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.