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. Battery voltage is then applied through the LT PARK and RT PARK LAMP fuses and the park lamp supply voltage circuits 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 Parklamp Switch parameter while cycling the headlamp switch between the Park and Off positions. The parameter should cycle between Active and Inactive.

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

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

⇒	If any of the parking lamps are always OFF or remain always ON, refer to the appropriate Park, License, and/or Tail Lamps Circuit Test -- Domestic or Export.

⇒	If just the license lamps on an export vehicle are always OFF, refer to License Lamps Circuit Test -- Export

Caution: The high intensity discharge system produces high voltage and current. To reduce the risk of severe shocks and burns:

Headlamp Switch Circuit Test

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Ignition OFF, 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 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, License, and/or Tail Lamps Circuit Test -- Domestic

1. Ignition OFF, disconnect the PRK LAMP Relay from the rear fuse block.
2. Ignition ON, verify that a test lamp does not illuminate between the supply voltage circuit terminal 104 and ground.

⇒	If the test lamp illuminates, test the supply voltage circuits for a short to voltage.

3. Verify that a test lamp illuminates between the B+ circuit terminal 102 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 100 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 B+ circuit terminal 102 and the control circuit terminal 101.
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. Disconnect the harness connector at the inoperative lamp.
8. Ignition OFF, test for less than 5.0 ohms of resistance between the appropriate ground circuit terminal listed below and ground.

•	Front Park and Marker Lamp terminal A

•	Tail Lamp terminal C

•	License Lamp terminal B

•	Middle Park Lamp terminal B (V4U)

•	Rear Park Lamp terminal B (V4U or B9Q)

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

9. Connect a test lamp between the inoperative lamp supply voltage circuit terminal listed below and ground.

•	Front Park and Marker Lamp terminal B

•	Tail Lamp terminal F

•	License Lamp terminal A

•	Middle Park Lamp terminal A (V4U)

•	Rear Park Lamp terminal A (V4U or B9Q)

10. Connect a 3A fused jumper wire between the B+ circuit terminal 100 and the supply voltage circuit terminal 104. Verify the test lamp is illuminated.

⇒	If the test lamp does not illuminate, test the supply voltage circuit for an open/high resistance. If the circuit tests normal, test or replace the bulb or lamp assembly.

11. If all circuits test normal, test or replace the park lamp relay.

Park, and/or Tail Lamps Circuit Test -- Export

1. Ignition OFF, disconnect the appropriate PRK LAMP Relay or the RT PRK LAMP Relay from the rear fuse block.
2. Ignition ON, verify that a test lamp does not illuminate between the appropriate supply voltage circuit terminal listed below and ground.

•	PRK LAMP Relay terminal 104

•	RT PRK LAMP Relay terminal 94

⇒	If the test lamp illuminates, test the supply voltage circuits for a short to voltage.

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

•	PRK LAMP Relay terminal 102

•	RT PRK LAMP Relay terminal 90

⇒	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 appropriate B+ circuit terminal listed below and ground.

•	PRK LAMP Relay terminal 100

•	RT PRK LAMP Relay terminal 93

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

5. Connect a test lamp between the appropriate B+ circuit terminal and the control circuit terminal listed below.

•	PRK LAMP Relay terminal 101 and terminal 102

•	RT PRK LAMP Relay terminal 92 and terminal 93

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. Disconnect the harness connector at the inoperative lamp.
8. Ignition OFF, test for less than 5.0 ohms of resistance between the appropriate ground circuit terminal listed below and ground.

•	Front Park and Marker Lamp terminal A

•	Tail Lamp terminal H

•	License Lamp terminal B

•	Middle Park Lamp terminal B (V4U)

•	Rear Park Lamp terminal B (V4U or B9Q)

•	Position Lamp terminal A (T72)

•	Position Lamp terminal H ( T84)

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

9. Connect a test lamp between the inoperative lamp supply voltage circuit listed below and ground.

•	Front Park and Marker Lamp terminal B

•	Tail Lamp terminal F

•	License Lamp terminal A

•	Middle Park Lamp terminal A (V4U)

•	Rear Park Lamp terminal A (V4U or B9Q)

•	Position Lamp terminal G-- Export

10. Connect a 3A fused jumper wire between the appropriate relay B+ circuit terminal and the supply voltage circuit terminal listed below. Verify the test lamp is illuminated.

•	PRK LAMP Relay terminal 100 and terminal 104

•	RT PRK LAMP Relay terminal 90and terminal 94

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

11. If all circuits test normal, test or replace the park lamp relay.

License Lamp Circuit Test -- Export

1. Ignition OFF, disconnect the EXP LIC LAMP Relay from the rear fuse block.
2. Ignition OFF, test for less than 5 ohms of resistance between the ground circuit terminal 9 and ground.

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

3. Ignition ON, verify that a test lamp does not illuminate between the supply voltage circuit terminal 10 and ground.

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

4. Park lamps ON, verify that a test lamp illuminates between the supply voltage circuit terminal 6 and ground.

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

5. Park lamps ON, verify that a test lamp illuminates between the supply voltage circuit terminal 8 and ground.

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

6. Ignition OFF, disconnect the harness connector at the inoperative license lamp.
7. Ignition OFF, test for less than 5.0 ohms of resistance between the ground circuit terminal B and ground.

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

8. Connect a test lamp between the supply voltage circuit terminal A and ground.
9. Connect a 3A fused jumper wire between the relay supply voltage circuit terminal 10 and B+. The test lamp should illuminate.

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

10. If all circuits test normal, test or replace the EXP LIC LAMP Relay.

Headlamp Switch

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Test for less than 2.0 ohms of resistance between the signal terminal 2 and the ground terminal 8 with the switch in the Park position.

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

3. Test for less than 2.0 ohms of resistance between the signal terminal 2 and the ground terminal 8 with the switch in the Headlamp position.

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

Relay Test

1. Ignition OFF, disconnect the relay.
2. Test for 70-100 ohms of resistance between terminals 85 and 86.

⇒	If the resistance is not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

•

30 and 85

•

30 and 86

•

30 and 87

•

85 and 87

⇒	If not the specified value, replace the relay.

4. Install a 10A fused jumper wire between relay terminal 85 and B+. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms of resistance between terminals 30 and 87.

⇒	If greater than the specified range, replace the relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.