The headlamp may be turned on 2 different ways. First, when the driver places the headlamp switch in the ON position, for manual operation. Second, with the headlamp switch placed in the OFF position activating automatic lamp control (ALC). The Left High Beam, Right High Beam, Left Low Beam, and Right Low Beam fuses in the fuse block - underhood, supply battery positive voltage to both low and high beam lamps at all times. For manual operation, when the headlamp switch is in the ON position, the headlamp switch supplies ground directly to the headlamps and to the body control module (BCM) on the headlamp low or high beam signal circuit, depending on the position of the headlamp dimmer switch. The BCM uses this signal to determines if the conditions are present to illuminate the daytime running lamps or park lamps.

A short to voltage, short to ground in the headlamp switch may cause a malfunction to occur.

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 on the headlamps ON with the headlamp switch. Cycle the headlamp setting on the multifunction switch between high and low beams. Observes the headlamps, the headlamps should cycle between high and low beam as well.

Multifunction/Headlamp Switch Circuit Testing

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Test for less than 1 ohm of resistance between the ground circuit and ground.

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

3. Install a 3-amp fused jumper wire between the signal circuit and ground. Verify the headlamps are ON.

⇒	If the headlamps are not ON, test the signal circuit of the headlamp switch for a short to voltage or an open/high resistance.

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

Multifunction/Headlamp Switch Testing

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

⇒	If less than infinite resistance, replace the headlamp switch.

3. Test for less than 1.5 ohms between the signal terminal and the high voltage supply terminal with the switch in the closed position.

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.