B178E

B178E-11-HEADLAMP SWITCH INPUT - CIRCUIT SHORT TO GROUND





For a complete wiring diagram, refer to the Wiring Information.

Theory of Operation

The Body Control Module (BCM) receives an input voltage from the headlamp switch. The BCM monitors the headlamp switch voltage and controls the exterior lighting functions based on the switch input. For additional information on Headlamp Switch operation, Headlamp Switch - Operation.

- When Monitored:
With the ignition on.

- Set Condition:
The BCM detects a low condition on the (L307) Headlamp Switch MUX circuit.





1. CHECK FOR ACTIVE DTC
1. Turn the ignition on.
2. With the scan tool, read the DTCs.

Does the scan tool display DTC: B178E-11-HEADLAMP SWITCH INPUT - CIRCUIT SHORT TO GROUND as active?

Yes

- Go To 2

No

- Test complete, 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.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

2. CHECK THE HEADLAMP SWITCH FOR AN INTERNAL SHORT TO GROUND
1. Turn the ignition off.
2. Disconnect the Headlamp Switch harness connector.
3. Turn the ignition on.
4. With the scan tool, read the DTCs.

Does the scan tool display DTC: B178E-11-HEADLAMP SWITCH INPUT - CIRCUIT SHORT TO GROUND as active?

Yes

- Go To 3

No

- Replace the Headlamp Switch. Headlamp Switch - Removal.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

3. CHECK THE (L307) HEADLAMP SWITCH MUX CIRCUIT FOR A SHORT TO GROUND




1. Turn the ignition off.
2. Disconnect the BCM G harness connector.
3. Measure the resistance between ground and the (L307) Headlamp Switch MUX circuit.

Is the resistance above 10K Ohms?

Yes

- Go To 4

No

- Repair the short to ground on the (L307) Headlamp Switch MUX circuit.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

4. CHECK THE (L307) HEADLAMP SWITCH MUX CIRCUIT FOR A SHORT TO THE (L900) HEADLAMP SWITCH MUX RETURN CIRCUIT




1. Measure the resistance between the (L307) Headlamp Switch MUX circuit and the (L900) Headlamp Switch MUX Return circuit.

Is the resistance above 10K Ohms?

Yes

- Replace the BCM. Body Control Module - Removal.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

No

- Repair the short between the (L307) Headlamp Switch MUX circuit and the (L900) Headlamp Switch MUX Return circuit.
- Perform the BODY VERIFICATION TEST. Body Verification Test.