Voltage is applied at all times to the low beam headlamp relay from battery voltage. The low beam headlamp relay is soldered to the Underhood Fuseblock. The replacement of the relay is accomplished by replacing the underhood fuseblock. Two different inputs to the body control module (BCM) can turn ON the low beam headlamps. The headlamp switch and the ambient light sensor.

Automatic Headlamps Operation

When the ambient light sensor detects a low light condition, the BCM then applies a ground to the headlamp low beam relay control circuit. This engages the headlamp relay and applies voltage through the headlamp fuses to the low beam headlamps.

Headlamp Switch Operation

When the headlamp switch is placed in the ON position, ground is applied to the BCM through the headlamp switch circuit. The BCM then applies a ground to the headlamp low beam relay control circuit. This engages the headlamp relay and applies voltage through the headlamp fuses to the low beam headlamps.

The ignition is ON. The headlamps must be commanded ON by either the BCM or by the headlamp switch.

The BCM detects a short to voltage on the low beam headlamps relay control circuit while trying to apply a ground to the circuit.

The low beam headlamps are not illuminated.

The BCM clears this code from current when the fault is removed from the system.

Schematic Reference

Headlights/Daytime Running Lights (DRL) Schematics

Connector End View Reference

Lighting Systems Connector End Views

Electrical Information Reference

Scan Tool Reference

Ignition ON, turn the headlamps ON. The headlamps should illuminate.

1. Ignition ON, automatic head lights OFF, verify the scan tool LOW BEAM PCB relay command parameter displays ON with the head lamp switch in the ON position.

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If the scan tool displays OFF, test the head lamp switch portion of the multifunction switch head lamps ON signal circuit terminal C1 pin 2 and head lamp switch ground circuit terminal C1 pin 1 for a short to voltage or an open/high resistance. If the circuits test normal, replace the multifunction switch.

2. Ignition OFF, disconnect the LOW BEAM PCB relay at the C2 pin 18 terminal (low beam relay control circuit coil side) of the Underhood Fuseblock.
3. Verify that a test lamp illuminates between the underhood fuseblock B+ circuit on the coil side and switch side of the relay when connected to ground.

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If the test lamp does not illuminate, test the underhood fuseblock 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 left and right low beam supply voltage circuits for a short to ground. If the circuits test normal replace the appropriate head lamp assembly.

4. Disconnect the harness connector at an inoperative head lamp assembly.
5. Test for less than 1.0 ohm of resistance between the inoperative head lamp ground circuit terminal 2 and ground.

⇒	If greater than 1.0 ohm, test the ground circuit for an open/high resistance.

6. Connect the harness connector at the head lamp.
7. Connect a 30-amp fused jumper wire between the B+ circuit terminal and the appropriate head lamp supply voltage circuit terminal of the low beam head lamp. Verify the head lamps illuminate.

⇒	If the head lamps do not illuminate, test the left and right head lamp supply voltage circuits for an open/high resistance. If the circuits test normal, replace the inoperative head lamp assembly.

8. Connect a test lamp between the underhood fuseblock B+ circuit terminal of the relay and the Low Beam relay control terminal C2 pin 18 circuit terminal.
9. Command the LOW BEAM PCB relay 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 low beam relay control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

10. If all circuits test normal, replace the underhood fuseblock.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.