The vehicle headlamps are controlled by the body control module (BCM) based on inputs from the headlamp switch and the turn signal/multifunction switch. The headlamp switch has four positions: Off, Auto, Park, and Headlamps. The default headlamp switch position is the Auto position, which the BCM uses the ambient light sensor to determine when headlamps are needed. The Off position of the headlamp switch is a momentary switch that overrides the automatic headlamps and turns off the vehicle headlamps. When the headlamp switch is in the Park position, the park lamp switch signal circuit is pulled low signaling the BCM to illuminate the vehicle parking lamps. With the headlamp switch in the Headlamps ON position, the headlamp switch ON signal circuit and the park lamp switch signal are both pulled low signaling the BCM to illuminate the headlamps and the tail/park lamps.

The headlamp high beams are controlled through the headlamp dimmer switch and the flash to pass switch, both located in the turn signal/multifunction switch. The flash to pass switch is a momentary type switch, designed to illuminate the high beams as long as the switch is held. With the switch closed, the flash to pass switch signal circuit is grounded, prompting the BCM to turn on the high beam lamps. The headlamp dimmer switch allows the operator to select between full time high or low beam operation. Unlike the flash to pass switch, it is not a momentary switch. When the headlamp dimmer switch is in the high beam position, the headlamp dimmer switch high beam signal circuit is grounded. This signals the BCM to turn on the high beam headlamps.

The BCM controls the headlamps based on the inputs explained above. When a low beam request is received, the BCM grounds the headlamp low beam relay control circuit energizing the LOW BEAM PCB Relay. With the low beam relay energized, B+ is applied through the switch side of the relay, both LO BEAM fuses, and the low beam supply voltage circuits illuminating the low beam headlamps. When a high beam request is received, the BCM grounds the headlamp high beam relay control circuit energizing the HIGH BEAM PCB Relay. With the high beam relay energized, B+ is applied through the switch side of the relay, both HI BEAM fuses, and the high beam supply voltage circuits illuminating the high beam headlamps.

Schematic Reference

Headlights/Daytime Running Lights (DRL) 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

1. Ignition ON, observe the scan tool Auto Hdlp. Disable Sw. parameter while cycling the headlamp switch between the Auto and Off positions. The reading should change between Active and Inactive.

⇒	If the reading does not change between the specified values, refer to Headlamp Switch Malfunction.

2. Turn the headlamp switch to the PARK position and observe the scan tool Headlamp Switch parameter. The reading should be Inactive.

⇒	If not the specified value, refer to Headlamp Switch Malfunction.

3. Observe the scan tool Headlamp Switch parameter while cycling the headlamp switch between the Auto and Headlamps ON position. The reading should change between Active and Inactive.

⇒	If the reading does not change between the specified values, refer to Headlamp Switch Malfunction.

4. With the headlamps ON, observe the scan tool Flash to Pass Switch parameter while pulling and releasing the dimmer switch. The reading should change between Active and Inactive.

⇒	If the reading does not change between the specified values, refer to Turn Signal/Multifunction Switch Malfunction.

5. With the headlamps ON, observe the scan tool High Beam Select Switch parameter while switching the headlamp dimmer switch between the low and high beam positions. The reading should change between Active and Inactive.

⇒	If the reading does not change between the specified values, refer to Turn Signal/Multifunction Switch Malfunction.

6. Observe the low beam headlamps while commanding the Low Beams ON and OFF with a scan tool. The low beam headlamps should turn ON and OFF when changing between the commanded states.

⇒	If the low beam headlamps do not turn ON and OFF while changing between the commanded states, refer to Headlamp Malfunction - Low Beam.

7. Observe the high beam headlamps while commanding the High Beams ON and OFF with a scan tool. The high beam headlamps should turn ON and OFF when changing between the commanded states.

⇒	If the high beam headlamps do not turn ON and OFF while changing between the commanded states, refer to Headlamp Malfunction - High Beam.

8. With the high beam headlamps ON, the instrument panel cluster (IPC) high beam indicator should be illuminated.

⇒	If the high beam indicator is not illuminated, refer to High Beam Indicator Malfunction.

Headlamp Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Test for less than 5 ohms between the ground circuit terminal 8 and ground.

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

3. Ignition ON, verify the scan tool Auto Hdlp. Disable Sw. parameter is Inactive.

⇒	If not the specified value, test the signal circuit terminal 3 for a short to ground. If the circuit tests normal, replace the BCM.

4. Ignition ON, verify the scan tool Headlamp ON Switch parameter is Inactive.

⇒	If not the specified value, test the signal circuit terminal 1 for a short to ground. If the circuit tests normal, replace the BCM.

5. Ignition ON, verify the scan tool Parklamp Switch parameter is Inactive.

⇒	If not the specified value, test the signal circuit terminal 2 for a short to ground. If the circuit tests normal, replace the BCM.

6. Install a 3A fused jumper wire between the signal circuit terminal 3 and ground. Verify the scan tool Parklamp Switch parameter is Active.

⇒	If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

7. Install a 3A fused jumper wire between the signal circuit terminal 2 and ground. Verify the scan tool Parklamp Switch parameter is Active.

⇒	If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

8. Install a 3A fused jumper wires between the signal circuit terminal 1 and ground. Verify the scan tool Headlamp Switch parameter is Active.

⇒	If not the specified value, test the signal circuit terminal 1 for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

9. If all circuits test normal, replace the headlamp switch.

Turn Signal/Multifunction Switch Malfunction

1. Ignition OFF, disconnect the X2 harness connector at the turn signal/multifunction switch.
2. Test for less than 5 ohms between the ground circuit terminal D and ground.

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

3. Ignition ON, verify the scan tool Flash to Pass Switch parameter is Inactive.

⇒	If not the specified value, test the signal circuit terminal E for a short to ground. If the circuit tests normal, replace the BCM.

4. Ignition ON, verify the scan tool High Beam Select Switch parameter is Inactive.

⇒	If not the specified value, test the signal circuit terminal C for a short to ground. If the circuit tests normal, replace the BCM.

5. Install a 3A fused jumper wire between the signal circuit terminal E and ground. Verify the scan tool Flash to Pass Switch parameter is Active.

⇒	If not the specified value, test the signal circuit for a short to voltage or and open/high resistance. If the circuit tests normal, replace the BCM.

6. Install a 3A fused jumper wire between the signal circuit terminal C and ground. Verify the scan tool High Beam Select Switch parameter is Active.

⇒	If not the specified value, test the signal circuit for a short to voltage or and open/high resistance. If the circuit tests normal, replace the BCM.

7. If all circuits test normal, test or replace the turn signal/multifunction switch.

Headlamp Malfunction - Low Beam

1. Ignition OFF, disconnect the X3 harness connector at the underhood fuse block.
2. Connect a test lamp between the relay control circuit terminal 39 and ground.
3. Ignition ON, command the Low Beams ON and OFF with a scan tool. The test lamp should turn ON and OFF between the commanded states.

⇒	If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM

4. Ignition OFF, connect the X3 harness connector at the underhood fuse block.
5. Ignition OFF, disconnect the harness connector at the inoperative low beam headlamp.
6. Test for less than 5 ohms between the inoperative ground circuit terminal listed below and ground.

•	Terminal B - with V22

•	Terminal A - w/o V22

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

7. Connect a test lamp between the appropriate control circuit terminal listed below and ground.

•	Terminal A - with V22

•	Terminal C - w/o V22

8. Ignition ON, command the Low Beams ON and OFF with a scan tool. The test lamp should turn ON and OFF between the commanded states.

⇒	If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the underhood fuse block.

⇒	If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the underhood fuse block.

9. If all circuits test normal, test or replace the inoperative low beam headlamp.

Headlamp Malfunction - High Beam

1. Ignition OFF, disconnect the X3 harness connector at the underhood fuse block.
2. Connect a test lamp between the relay control circuit terminal 44 and ground.
3. Ignition ON, command the High Beams ON and OFF with a scan tool. The test lamp should turn ON and OFF between the commanded states.

⇒	If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM

4. Ignition OFF, connect the X3 harness connector at the underhood fuse block.
5. Ignition OFF, disconnect the harness connector at the inoperative high beam headlamp.
6. Test for less than 5 ohms between the inoperative ground circuit terminal listed below and ground.

•	Terminal B - with V22

•	Terminal A - w/o V22

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

7. Connect a test lamp between the appropriate control circuit terminal listed below and ground.

•	Terminal A - with V22

•	Terminal B - w/o V22

8. Ignition ON, command the High Beams ON and OFF with a scan tool. The test lamp should turn ON and OFF between the commanded states.

⇒	If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the underhood fuse block.

⇒	If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the underhood fuse block.

9. If all circuits test normal, test or replace the inoperative high beam headlamp.

High Beam Indicator Malfunction

Ignition ON, perform the IPC Display Test with a scan tool. The IPC high beam indicator should illuminate.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.