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, in 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 on 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 coil in the PARK LP PCB relay, causing the relay switch to close. This then applies B+ to the left and right exterior lamps through the LT PARK and RT PARK fuses, illuminating the exterior lamps.

Schematic Reference

Exterior Lights Schematics

Connector End View Reference

Lighting Systems Connector End Views

Description and Operation

Exterior Lighting Systems Description and Operation

Electrical Information Reference

Scan Tool Reference

1. Ignition ON, observe the scan tool BCM Parklamp Switch parameter while cycling the headlamp switch between the Park and Off positions. The parameter should change between Active and Inactive.

⇒	If the parameter does not change between the specified values, refer to Headlamp Switch Circuit Malfunction.

2. Command the Parking Lamps ON and OFF with a scan tool. The front park, license, and tail lamps should turn ON and OFF when changing between the commanded states.

⇒	If all of the lamps are always OFF or remain ON, refer to the Park Lamp Relay Test.

⇒	If one or more of the lamps is always OFF, refer to Park Lamps Circuit Malfunction.

Headlamp Switch Circuit Malfunction

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Verify that a test lamp illuminates between the ground circuit terminal 8 and B+.

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

3. Ignition ON, verify the scan tool BCM 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 Lamp Relay Test

1. Ignition OFF, disconnect the harness connector C2 at the underhood fuse block.
2. Connect a test lamp between the control circuit terminal K2 and B+.
3. Ignition ON, command the Park 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.

4. If the circuit tests normal, replace the underhood fuse block.

Park Lamps Circuit Malfunction

1. Ignition OFF, disconnect the harness connector at the inoperative exterior lamp.
2. Ignition OFF, test for less than 5.0 ohms between the appropriate ground circuit terminal listed below and ground.

•	Marker Lamps terminal B

•	Tail Lamps terminal B

•	License lamp terminal B

•	Tail/Stop/Turn Signal Lamp terminal G

•	Front Park/Turn Signal Lamp terminal G

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

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

•	Marker Lamps terminal A

•	Tail Lamps terminal A

•	License lamp terminal A

•	Tail/Stop/Turn Signal Lamp terminal B

•	Front Park/Turn Signal Lamp terminal B

4. Ignition ON, command the Park Lamps ON and OFF with a scan tool. The park lamps 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 circuit tests normal, replace the underhood fuse block.

⇒	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 underhood fuse block.

5. If all circuits test normal, test or replace the lamp bulb.

Headlamp Switch

Important: If the switch tests open in any switch position other than Auto, test the switch signal circuits for a short to voltage before replacing the switch.

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Test for infinite resistance between the signal terminal 1 and the ground terminal 8 with the switch in the Auto position.

⇒	If not the specified value, replace the headlamp switch.

3. Test for less than 2.0 ohms between the signal terminal 1 and the ground terminal 8 with the switch in the Headlamp position

⇒	If greater than the specified value, replace the headlamp switch.

4. Test for infinite resistance between the signal terminal 2 and the ground terminal 8 with the switch in the Auto position.

⇒	If not the specified value, replace the headlamp switch.

5. Test for less than 2.0 ohms between the signal terminal 2 and the ground terminal 8 with the switch in the Park position.

⇒	If greater than the specified value, replace the headlamp switch.

6. Test for infinite resistance between the signal terminal 3 and the ground terminal 8 with the switch in the Auto position.

⇒	If not the specified value, replace the headlamp switch.

7. Test for less than 2.0 ohms between the signal terminal 3 and the ground terminal 8 with the switch in the Off position.

⇒	If greater than the specified value, replace the headlamp switch.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.