Diagnosis And Testing - Exterior Lighting: Headlamps

NOTE:

As part of the exterior lighting fail safe feature, upon ignition ON all exterior park lamps and the headlight low beams will illuminate regardless of the headlight switch control knob position if the IC cannot detect an input from the headlight switch, or if there is a loss of communication between the multi-function switch/Steering Column Control Module (SCCM) microcontroller and the BCM. Diagnose and repair those problems before attempting to repair the headlights. In addition, the BCM will store a DTC for an open or shorted headlight circuit.

CONDITION	POSSIBLE CAUSES	CORRECTION
HEADLAMP DOES NOT ILLUMINATE	1. Ineffective or missing HID lighting element.	1. Test and replace HID lighting element if required.
	2. Ineffective ground circuit.	2. Test and repair open headlight ground circuit if required.
	3. Ineffective feed circuit.	3. Test and repair open headlight low beam or high beam feed circuit if required.
	4. Ineffective switch.	4. Test and replace the headlight switch if required.
	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 headlight low beam or high beam feed circuit if required.
	2. Ineffective switch.	2. Test and replace headlight switch if required.
	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 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 SCCM microcontroller inputs or outputs.	1. Use a diagnostic scan tool and the appropriate diagnostic information for further SCCM microcontroller 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.