Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Diagnostic Test
- CHECK FOR AN ACTIVE DTC
- Turn the ignition on.
- Turn the Headlamps on.
- With the scan tool, read the Body Control Module (BCM) DTCs and record on the repair order.
Is the DTC active?
Yes
- Go To 2
No
- The condition or conditions that originally set this DTC are not present at this time. Using the wiring diagrams as a guide, check all related splices and connectors for signs of water intrusion, corrosion, pushed out or bent terminals and correct pin tension. If no problems are found, test complete.
- Perform the BODY VERIFICATION TEST. Refer to BODY VERIFICATION TEST .
- CHECK THE HEADLAMP SWITCH
- Turn the ignition off.
- Disconnect the Headlamp Switch harness connector.
- Turn the ignition on.
- With the scan tool, read the BCM DTCs.
Is the DTC active?
Yes
- Go To 3
No
- Replace the Headlamp Switch in accordance with the Service Information. Refer to SWITCH, HEADLAMP, REMOVAL .
- Perform the BODY VERIFICATION TEST. Refer to BODY VERIFICATION TEST .
- CHECK THE (L307) HEADLAMP SWITCH MUX CIRCUIT FOR A SHORT TO GROUND
- Turn the ignition off.
- Disconnect the BCM C7/G harness connector.
- Check for continuity between ground and the (L307) Headlamp Switch MUX circuit at the Headlamp Switch harness connector.
Is there continuity between ground and the (L307) Headlamp Switch MUX circuit?
Yes
- Repair the short to ground on the (L307) Headlamp Switch MUX circuit.
- Perform the BODY VERIFICATION TEST. Refer to BODY VERIFICATION TEST .
No
- Go To 4
- CHECK THE (L307) HEADLAMP SWITCH MUX CIRCUIT FOR A SHORT TO THE (L900) HEADLAMP SWITCH MUX RETURN CIRCUIT
- Check for continuity between the (L307) Headlamp Switch MUX circuit and the (L900) Headlamp Switch MUX Return circuit at the BCM C7/G harness connector.
Is there continuity between the (L307) Headlamp Switch MUX circuit and the (L900) Headlamp Switch MUX Return circuit?
Yes
- Repair the short between the (L307) Headlamp Switch MUX circuit and the (L900) Headlamp Switch MUX Return circuit.
- Perform the BODY VERIFICATION TEST. Refer to BODY VERIFICATION TEST .
No
- Replace the Body Control Module (BCM) in accordance with the Service Information. Refer to MODULE, BODY CONTROL (BCM), REMOVAL .
- Perform the BODY VERIFICATION TEST. Refer to BODY VERIFICATION TEST .
- Check for continuity between the (L307) Headlamp Switch MUX circuit and the (L900) Headlamp Switch MUX Return circuit at the BCM C7/G harness connector.
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.