Headlamps Inoperative - Low and High Beams

HEADLAMPS INOPERATIVE - LOW AND HIGH BEAMS




DIAGNOSTIC FAULT INFORMATION

IMPORTANT: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Testing and Inspection

CIRCUIT/SYSTEM DESCRIPTION
With the headlamp switch in the HEAD position, the headlamp switch headlamp ON signal circuit is grounded through the turn signal/multifunction switch at G201. In response to this input, the body control module (BCM) provides ground to either the headlamp low beam relay control circuit through the headlamp switch signal circuit or the headlamp high beam relay control circuit. The position of the headlamp dimmer switch determines which relay coil has ground. The BCM supplies ground to the relay coil circuits, if the headlamps are necessary. The underhood fuse block supplies battery positive voltage to both relay switch circuits. When the low beam relay coil is energized, current flows through the LH LOW and the RH LOW fuses to the low beam headlamps. When the headlamp high beam relay coil is energized, current flows through the LH HIGH and the RH HIGH fuses to the high beam headlamps. Ground for the left headlamp assembly is provided at G101. Ground for the right headlamp assembly is provided at G102.

CIRCUIT/SYSTEM TESTING
1. Ignition OFF, disconnect the turn signal/multifunction switch C1 harness connector.
2. Connect a 3-amp fused jumper between the headlamp switch headlamps on signal circuit and ground.
3. Ignition ON, install a scan tool and observe the Headlamp ON switch parameter. The scan tool should display Active.
- If the scan tool indicates the Headlamp ON Switch parameter is Inactive, repair an open/high resistance in the headlamp switch headlamps on signal circuit. If the circuit tests normal, replace the BCM.
4. With the scan tool observe the Headlamp OFF switch parameter. The scan tool should display OFF.
- If the scan tool indicates the Headlamp OFF Switch parameter is ON, repair a short to ground in the headlamp switch headlamps off signal circuit. If the circuit tests normal, replace the BCM.
5. Ignition OFF, connect the turn signal/multifunction switch C1 harness connector.
6. Disconnect the C2 harness connector at the turn signal/multifunction switch.
7. Connect a 3-amp fused jumper between the low beam relay control circuit and the headlamp switch signal circuit.
8. Ignition ON, place the headlamp switch in the ON position. The low beam headlamps should illuminate.
- If the low beam headlamps do not illuminate, repair the headlamp switch signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
9. If all circuits test normal, test or replace the turn signal/multifunction switch.

REPAIR INSTRUCTIONS

IMPORTANT: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

- Multifunction, Turn Signal Switch Replacement
- Control Module References for BCM replacement, setup, and programming