The vehicle park, license, and tail lamps are controlled by the body control module (BCM) based on an input from the headlamp switch. The headlamp switch has four positions: Off, Auto, Park, and Headlamps. The default headlamp switch position is Auto, which the BCM uses the ambient light sensor to determine when exterior lamps are needed. The Off portion of the headlamp switch is a momentary switch which overrides the automatic lamps and will turn off the vehicle lamps. The Park position of the headlamp switch will only illuminate the vehicle parking lamps. The Headlamp position of the headlamp switch will illuminate both the parking lamps, as well has the headlamps. With the headlamp switch in the Park position, the park lamp switch signal circuit is grounded, prompting the BCM to turn on the exterior lamps, regardless of other factors such as ambient light.

When a park lamp request is received, the BCM grounds the park lamp relay control circuit. This energizes the PRK LAMP Relay and battery voltage is applied through the switch side of the relay, the exterior lamp fuses, and the supply voltage circuits illuminating the front park, license, tail, and marker lamps.

Schematic Reference

Exterior Lights Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Exterior Lighting Systems Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, observe the scan tool Park Lamp Switch parameter while cycling the park lamp switch ON and OFF. The readings should toggle between Active and Inactive.

⇒	If the readings do not change between the commanded states, refer to Park Lamp Switch Malfunction.

2. Ignition ON, command the Parking Lamps ON and OFF with a scan tool. The park, license, and marker lamps should turn ON and OFF between the commanded states.

⇒	If the lamps do not turn ON and OFF between the commanded states, refer to Park Lamp Malfunction.

Park Lamp Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Test for less than 5 ohms between the ground circuit terminal 8 and ground.

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

3. Ignition ON, verify the scan tool Parklamp Switch parameter is Inactive.

⇒	If not the specified value, test the signal circuit terminal 2 for a short to ground. If the circuit tests normal, replace the BCM.

4. Install a 3A fused jumper wire between the signal circuit terminal 2 and ground. Verify the scan tool Parklamp Switch parameter is Active.

⇒	If not the specified value, test the signal circuit for a short to voltage or and open/high resistance. If the circuit tests normal, replace the BCM.

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

Park Lamps Malfunction

1. Ignition OFF, disconnect the PRK LAMP Relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 30 and ground.

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

3. Verify that a test lamp illuminates between the B+ circuit terminal 85 and ground.

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

4. Verify that a test lamp illuminates between the B+ circuit terminal 87 and ground.

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

5. Connect a test lamp between the control circuit terminal 86 and the B+ circuit terminal 85.
6. Command the Parking Lamps 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 ON, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

7. If all of the circuits test normal, test or replace the PRK LAMP relay.
8. Ignition OFF, disconnect the harness connector at the inoperative exterior lamp.
9. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the appropriate ground circuit terminal listed below and ground.

•	Left Rear Tail/Stop and Turn Signal Lamp terminal G

•	Left Front Park/Turn Signal Lamp terminal G

•	Left Front Marker Lamp terminal B

•	License Lamp terminal B

•	Right Front Park/Turn Signal Lamp terminal G

•	Right Front Marker Lamp terminal B

•	Right Rear Tail/Stop and Turn Signal Lamp terminal G

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

10. Connect a test lamp between the appropriate control circuit terminal listed below and ground.

•	Left Rear Tail/Stop and Turn Signal Lamp terminal B

•	Left Front Park Lamp terminal B

•	Left Front Marker Lamp terminal A

•	License Lamp terminal A

•	Right Front Park/Turn Signal Lamp terminal B

•	Right Front Marker Lamp terminal A

•	Right Rear Tail/Stop and Turn Signal Lamp terminal B

11. Ignition ON, command the Parking Lamps 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 ON, test the control circuit for a short to voltage.

⇒	If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance.

12. If all circuits test normal, test or replace the inoperative park lamp.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.