1. Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
2. Review Strategy Based Diagnosis for an overview of the diagnostic approach.
3. Diagnostic Procedure Instructions provides an overview of each diagnostic category.

When the low beam is activated and the turn signal/multifunction switch is placed in the high beam position, the body control module (BCM) will receive a ground signal through the turn signal/multifunction switch signal circuit to illuminate the high beam lamps.

Low beam is ON and high beam is activated

The body control module (BCM) reports stuck turn signal/multifunction switch.

The condition for setting the DTC is no longer present.

Schematic Reference

Exterior Lights Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Exterior Lighting Systems Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, turn the headlamp switch in the low beam position. Push/pull the turn signal/multifunction switch between the ON/OFF position. The high beam lamps should be ON/OFF as the switch is cycled.

1. Ignition OFF, disconnect the S78 Turn Signal/Multifunction Switch harness connector. Test for less than 5 Ω between the ground circuit terminal 3 and ground.

⇒	If greater then the specified value, test the ground circuit for an open/high resistance.

2. Connect the S78 Turn Signal/Multifunction Switch harness connector.
3. Disconnect the X3 harness connector at the K9 Body Control Module (BCM).
4. Connect a test lamp between B+ and the signal circuit terminal 11(X3).
5. Push/pull the S78 Turn Signal/Multifunction Switch between the high beam and OFF position. The test lamp should turn ON and OFF as the switch is cycled.

⇒	If the test lamp is always OFF, test the signal circuit for a short to voltage or an open/high resistance. If the circuit test normal, replace the S78 Turn Signal/Multifunction Switch.

⇒	If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit test normal, replace the S78 Turn Signal/Multifunction Switch.

6. If all circuits test normal, replace the K9 Body Control Module (BCM).

Static Test

1. Ignition OFF, disconnect the S78 Turn Signal/Multifunction Switch harness connector. S78 Turn Signal/Multifunction Switch in flash position, test for less than 5 Ω between terminal 4 and terminal 3.

⇒	If greater than the specified value, replace the S78 Turn Signal/Multifunction Switch.

2. S78 Turn Signal/Multifunction Switch in high beam position, test for less than 5 Ω between terminal 2 and terminal 3.

⇒	If greater than the specified value, replace the S78 Turn Signal/Multifunction Switch.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.