When the park lamp switch is in the ON position, the instrument panel module (IPM) energizes the park lamp relay. With the park lamp relay energized, battery positive voltage is supplied through the DIMMING fuse to the instrument panel lamp fuse supply voltage circuit of the IPM. Upon receiving this voltage supply the IPM requests the status of the ambient light sensor from the climate control panel (CCP). The CCP sends a serial data message indicating a Light or Dark status of the ambient light sensor. The IPM will default to dark if the message is not received. If the status of the ambient light sensor is light, then the interior back lighting will not be activated. The IPM also receives an input from the instrument panel (I/P) dimmer switch. The IPM provides the I/P dimmer switch with a 5-volt reference voltage and ground. The I/P dimmer switch is a potentiometer that varies the input signal voltage to the IPM between 0.36-4.23 volts. This input determines the intensity level of the back lighting illumination. The driver may change intensity of the back lighting by positioning the I/P dimmer switch between the minimum and maximum settings. The IPM will default to full intensity if the input from the I/P dimmer switch is not within the specified values. Upon receipt of all the fore mentioned information, the IPM sends a serial data message to the CCP, IPC, radio, and all the door modules indicating the ON/OFF status and intensity level of the back lighting. The CCP, IPC, and radio incorporate vacuum fluorescent (VF) lamps that are illuminated at full intensity with the ignition in the ON position. The CCP, IPC, and radio will adjust the VF lamp intensity as requested by the IPM by varying the pulse width modulation of the power feed circuit to the VF lamps. When the door control modules receive the serial data message, each door module will supply pulse width modulation (PWM) voltage to the door switch LEDs at the requested intensity. The IPM also supplies voltage to all the remaining lamps at the proper PWM voltage to achieve the requested intensity. The PRNDL incorporates LED lamps that are illuminated at full intensity with the ignition in the ON position. When the park lamps are active, the IPC will adjust the PRNDL LED intensity as requested by the IPM by varying the pulse width modulation of the LED dimming signal circuit to the lamps. All interior back lighting lamps are permanently grounded.

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

Ignition ON, observe the scan tool Dimming Pot A/D parameter while operating the dimmer switch from high to low brightness. The parameter should change from a high count to a low count 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 low reference circuit terminal 1.

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

3. Ignition ON, verify the scan tool Dimming POT A/D parameter is greater than 140 counts.

⇒	If less than the specified range, test the signal circuit terminal 2 for a short to ground. If the circuit tests normal, replace the IPM.

4. Install a 3-A fused jumper wire between the signal circuit terminal 2 and the low reference circuit terminal 1. Verify the scan tool Dimming POT A/D parameter is less than 30 counts.

⇒	If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the IPM.

5. If all circuits test normal, test or replace the I/P dimmer switch.

Interior Backlighting Malfunction - Incandescent

1. Ignition OFF, disconnect the X1 harness connector at the IPM.
2. Ignition ON, park lamps ON, verify that a test lamp illuminates between the park lamp voltage supply circuit terminal 1 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 ON, park lamps OFF, verify that a test lamp does not illuminate between the control circuit terminal 1 and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to voltage.

4. Ignition OFF, disconnect the harness connector at the component with the inoperative 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 control circuit and ground.
7. 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 IPM

⇒	If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the IPM.

8. If all circuits test normal, test or replace the component with the inoperative incandescent backlighting.

Interior Backlighting Malfunction - LED

1. Ignition OFF, disconnect the harness connector at the component with the inoperative LED 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 LED dimming control circuit and ground.
4. 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 HVAC control module.

⇒	If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the HVAC control module.

5. If all circuits test normal, test or replace the component with the inoperative LED backlighting.

Door Switch/Rear Compartment Release Switch Indicator Malfunction

1. Ignition OFF, disconnect the harness connector at the component with the inoperative 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 backlight lamp control circuit and ground.
4. Command the appropriate door module Door Switch Backlighting 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 appropriate door control module.

⇒	If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the appropriate door control module.

5. If all circuits test normal, test or replace the component with the inoperative backlighting.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.