Headlamp Switch: Testing and Inspection

Before testing the headlamp switch, turn ON the exterior lighting and open the driver side front door. If the exterior lamps of the vehicle operate, but there is no chime warning issued with the driver side front door open, (Refer to ELECTRICAL/LAMPS/ LIGHTING - INTERIOR/DOOR AJAR SWITCH - DIAGNOSIS AND TESTING). If the exterior lamps of the vehicle are inoperative, but the chime warning is issued, (Refer to ELECTRICAL/LAMPS/LIGHTING - EXTERIOR - DIAGNOSIS AND TESTING).

If the exterior lamps and the chime warning are both inoperative, test the left multi-function switch. (Refer to ELECTRICAL/LAMPS/LIGHTING - EXTERIOR - DIAGNOSIS AND TESTING). If the multi-function switch tests OK, proceed as follows. The following tests will help to locate a short or open in the hard wired circuits between the multi-function switch and the Body Control Module (BCM). For complete circuit diagrams, refer to the appropriate wiring information.

WARNING: ON VEHICLES EQUIPPED WITH AIRBAGS, REFER TO ELECTRICAL, RESTRAINTS BEFORE ATTEMPTING ANY STEERING WHEEL, STEERING COLUMN, OR INSTRUMENT PANEL COMPONENT DIAGNOSIS OR SERVICE. FAILURE TO TAKE THE PROPER PRECAUTIONS COULD RESULT IN ACCIDENTAL AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL INJURY.

1. Disconnect and isolate the battery negative cable. Disconnect the instrument panel wire harness connector from the left multi-function switch connector. Disconnect the instrument panel wire harness connector from the Body Control Module (BCM). Check for continuity between the headlamp switch mux circuit of the instrument panel wire harness connector for the multi-function switch and a good ground. There should be no continuity. If OK, go to Step 2. If not OK, repair the shorted headlamp switch mux circuit.
2. Check for continuity between the headlamp switch mux circuit of the instrument panel wire harness connector for the multi-function switch and the instrument panel wire harness connector for the BCM. There should be continuity. If OK, go to Step 3. If not OK, repair the open headlamp switch mux circuit.
3. Check for continuity between the headlamp switch return circuit of the instrument panel wire harness connector for the multi-function switch and a good ground. There should be no continuity. If OK, go to Step 4. If not OK, repair the shorted headlamp switch return circuit.
4. Check for continuity between the headlamp switch return circuit of the instrument panel wire harness connector for the multi-function switch and the instrument panel wire harness connector for the BCM. There should be continuity If OK, use a DRB III scan tool and the proper Diagnostic Procedures to test the BCM. If not OK, repair the open headlamp switch return circuit.