Diagnosis And Testing: Headlamps

NOTE:

As part of the exterior lighting failsafe feature, upon ignition ON, all exterior park lamps and the headlamp low beams will illuminate regardless of the left multi-function switch control knob position if the SCCM cannot detect an input from the left multi-function switch, or if there is a loss of communication between the left multi-function switch IPC or between the IPC and the BCM. Diagnose and repair those problems before attempting to repair the Headlamps. In addition, the BCM will store a DTC for an open or shorted headlamp circuit.

CONDITION	POSSIBLE CAUSES	CORRECTION
HEADLAMP DOES NOT ILLUMINATE	1. Ineffective or missing bulb or HID ignitor.	1. Test and replace headlamp bulb or HID ignitor if required.
	2. Ineffective ground circuit.	2. Test and repair open headlamp ground circuit if required.
	3. Ineffective feed circuit.	3. Test and repair open headlamp low beam or high beam feed circuit if required.
	4. Ineffective IPC inputs or outputs.	4. Use a diagnostic scan tool and the appropriate diagnostic information for further IPC diagnosis.
	5. Ineffective BCM inputs or outputs.	5. Use a diagnostic scan tool to test the BCM inputs and outputs. Refer to the appropriate diagnostic information.
HEADLAMP DOES NOT EXTINGUISH	1. Ineffective feed circuit.	1. Test and repair shorted headlamp low beam or high beam feed circuit if required.
	2. Ineffective IPC inputs or outputs.	2. Use a diagnostic scan tool and the appropriate diagnostic information for further IPC diagnosis.
	3. Ineffective BCM inputs or outputs.	3. Use a diagnostic scan tool to test the BCM inputs and outputs. Refer to the appropriate diagnostic information.
HEADLAMPS ILLUMINATE WITH IGNITION ON AND HEADLAMP SWITCH OFF (FAIL-SAFE OPERATION)	1. Loss of Local Interface Network (LIN) or CAN data bus communication.	1. Test and repair the LIN or CAN data bus if required. Refer to the appropriate diagnostic information.
HEADLAMPS WILL NOT SWITCH FROM HIGH TO LOW BEAMS, OR FROM LOW TO HIGH BEAMS	1. Ineffective IPC inputs or outputs.	1. Use a diagnostic scan tool and the appropriate diagnostic information for further IPC diagnosis.
	2. Ineffective BCM inputs or outputs.	2. Use a diagnostic scan tool to test the BCM inputs and outputs. Refer to the appropriate diagnostic information.