B178E-15

B178E-15-HEADLAMP SWITCH INPUT - CIRCUIT SHORT TO BATTERY OR OPEN

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.





Diagnostic Test

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

Does the scan tool display this DTC 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 (L307) HEADLAMP SWITCH MUX CIRCUIT FOR A SHORT TO VOLTAGE
1. Turn the ignition off.
2. Disconnect the Headlamp Switch harness connector.
3. Turn the ignition on.
4. Measure the voltage of the (L307) Headlamp Switch MUX circuit.

Is the voltage above 5.0 volts?

Yes

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

No

- Go To 3

3. HEADLAMP SWITCH
1. Turn the ignition off.
2. Connect a jumper wire between ground and the (L307) Headlamp Switch MUX circuit at 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?

Yes

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

No

- Go To 4

4. CHECK THE (L307) HEADLAMP SWITCH MUX CIRCUIT FOR AN OPEN
1. Turn the ignition off.
2. Disconnect the BCM G harness connector.
3. Measure the resistance of the (L307) Headlamp Switch MUX circuit.

Is the resistance below 5.0 Ohms?

Yes

- Go To 5

No

- Repair the (L307) Headlamp Switch MUX circuit for an open.
- Perform the BODY VERIFICATION TEST. Body Verification Test .

5. CHECK THE (L900) HEADLAMP SWITCH MUX RETURN CIRCUIT FOR AN OPEN
1. Measure the resistance of the (L900) Headlamp Switch MUX Return circuit.

Is the resistance below 5.0 Ohms?

Yes

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

No

- Repair the (L307) Headlamp Switch MUX Return circuit for an open.
- Perform the BODY VERIFICATION TEST. Body Verification Test .