The underhood fuse block supplies battery voltage through the FRT POS fuse to the coil and switch terminals of the FRT POSITION LMP relay located in the underhood fuse block . The underhood fuse block also provides battery voltage to the PARK LP relay coil and switch terminals. When the headlamp switch is turned to the position lamp ON position, a signal is sent to the BCM to ground both the FRT POSITION LMP relay and PARK LP relay control circuits. This energizes the relays, closing the switch contacts and provides battery voltage to the front and rear position lamps. The front position lamps are permanently grounded at G105 and the rear position lamps are grounded at G420. With both power and ground, the position lamps illuminate. If the headlamps are activated by either the headlamp switch or the BCM in Automatic Lamp Control (ALC) mode, just the front position lamps will be disabled.

Schematic Reference

Exterior Lights Schematics

Connector End View Reference

Lighting Systems Connector End Views

Electrical Information Reference

Scan Tool Reference

1. Ignition On, observe the scan tool DRL Status data parameter while toggling the headlamp switch between the position lamps ON and OFF positions.

⇒	If the parameter does not change between states, test the position lamps switch signal circuit for an open, high resistance or short to ground. If the circuit tests normal, test or replace the headlamp switch.

2. Ignition OFF, disconnect the FRT POSITION LMP relay.
3. Ignition ON, verify that a test lamp does not illuminate between the relay controlled output circuit and ground.

⇒	If the test lamp illuminates, test the relay controlled output circuit for a short to voltage.

4. Verify that a test lamp illuminates between the relay coil B+ circuit and ground.

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If the test lamp does not illuminate, test the relay coil B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the relay controlled output circuit for a short to ground. If the circuit tests normal, test or replace the front position lamp relay.

5. Verify that a test lamp illuminates between the relay switch B+ circuit and ground.

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

6. Disconnect the harness connector at the inoperative position lamp.
7. Test for less than 1.0 ohm of resistance between the inoperative position lamp ground circuit terminal 1 and ground.

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

8. Connect the harness connector at the inoperative position lamp.
9. Connect a 10A fused jumper wire between the relay switch B+ circuit and the relay controlled output circuit. Verify the position lamps are activated.

⇒	If the position lamps do not activate, test the relay controlled output circuit for an open/high resistance. If the circuit tests normal, test or replace the inoperative position lamp bulb.

10. Connect a test lamp between the relay coil B+ circuit and the relay coil control circuit.
11. Command the position lamps ON and OFF with the scan tool utilizing the Daytime Running Lamps output control. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the relay coil control circuit for a short to ground. If the circuit tests normal, replace the BCM.

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

12. If all circuits test normal, test or replace the position lamp relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.