With the headlamp switch in the HEAD position, the headlamp switch headlamp ON signal circuit is grounded through the turn signal/multifunction switch at G201. In response to this input, the body control module (BCM) provides ground to either the headlamp low beam relay control circuit through the headlamp switch signal circuit or the headlamp high beam relay control circuit. The position of the headlamp dimmer switch determines which relay coil has ground. The BCM supplies ground to the relay coil circuits, if the headlamps are necessary. The LO BEAM and HI BEAM relays are supplied with battery positive voltage at there coil and switch input circuits. When the low beam relay coil is energized, current flows through the LH LOW and the RH LOW fuses to the low beam headlamps. When the headlamp high beam relay coil is energized, current flows through the LH HIGH and the RH HIGH fuses to the high beam headlamps. The headlights may be switched to high beam with the movement of the headlamp dimmer switch lever. With the headlamp dimmer switch in the high beam position the BCM sends a message via GMLAN to the instrument panel cluster (IPC) requesting the IPC to illuminate the high beam indicator. Ground for the left headlamp assembly is provided at G101. Ground for the right headlamp assembly is provided at G102. For more detailed information concerning headlamp operation refer to Exterior Lighting Systems Description and Operation .

Schematic Reference

Headlights/Daytime Running Lights (DRL) Schematics

Connector End View Reference

Lighting Systems Connector End Views

Electrical Information Reference

Scan Tool Reference

1. Ignition ON, observe the scan tool headlamp off switch parameter while turning the headlamp switch ON and OFF. The reading should toggle between INACTIVE and ACTIVE.

⇒	If the reading does not change between the commanded states, refer to Headlamp Switch Malfunction.

2. Observe the scan tool flash to pass switch parameter while applying and releasing the flash to pass switch. The reading should toggle between ACTIVE and INACTIVE.

⇒	If the reading does not change between the commanded states, refer to Headlamp Switch Malfunction.

3. Observe the scan tool high beam select switch parameter while applying and releasing the high beam select switch. The reading should toggle between ACTIVE and INACTIVE.

⇒	If the reading does not change between the commanded states, refer to Headlamp Switch Malfunction.

4. Observe the scan tool headlamp on switch parameter while turning the headlamp switch ON and OFF. The reading should toggle between ACTIVE and INACTIVE.

⇒	If the reading does not change between the commanded states, refer to Headlamp Switch Malfunction.

Headlamp Switch Malfunction

1. Ignition OFF, disconnect the C1 and C2 harness connectors at the turn signal/multifunction switch.
2. Test for less than 1.0 ohm of resistance between the ground circuit terminal 1 and ground.

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

3. Test for less than 1.0 ohm of resistance between the ground circuit terminal B and ground.

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

4. Ignition ON, verify the scan tool headlamp off switch parameter is INACTIVE.

⇒	If not the specified value, test the signal circuit terminal 4 for a short to ground. If the circuit tests normal, replace the BCM.

5. Verify the scan tool flash to pass 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.

6. Verify the scan tool high beam select switch parameter is INACTIVE.

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

7. Verify the scan tool headlamp on 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.

8. Install a 3A fused jumper wire between the signal circuit terminal 4 and ground. Verify the scan tool headlamp off 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.

9. Install a 3A fused jumper wire between the signal circuit terminal C 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 an open/high resistance. If the circuit tests normal, replace the BCM.

10. Install a 3A fused jumper wire between the signal circuit terminal D 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 an open/high resistance. If the circuit tests normal, replace the BCM.

11. Install a 3A fused jumper wire between the signal circuit terminal 2 and ground. Verify the scan tool headlamp on 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.

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

Headlamps Malfunction - Low Beam

1. Ignition OFF, disconnect the low beam relay.
2. Ignition ON, verify that a test lamp does not illuminate between the relay switch controlled output circuit and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to voltage.

3. Verify that a test lamp illuminates between the relay switch B+ circuit and ground.

⇒

If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the relay switch controlled output circuit for a short to ground. If the circuit tests normal, test or replace the low beam relay.

4. Verify that a test lamp illuminates between the relay coil B+ circuit and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.

5. Disconnect the harness connector at the inoperative low beam headlamp.
6. Test for less than 1.0 ohm of resistance between the inoperative low beam headlamp ground circuit terminal D and ground.

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

7. Connect the harness connector at the inoperative low beam headlamp.
8. Connect a 20A fused jumper wire between the relay switch B+ circuit and the relay switch controlled output circuit. Verify the low beam headlamps are activated.

⇒	If the low beam headlamps do not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the inoperative low beam headlamp.

9. Connect a test lamp between the relay coil B+ circuit and the relay coil control circuit.
10. Command the low beam headlamps ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing 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.

11. If all circuits test normal, test or replace the low beam relay.

Headlamps Malfunction - High Beam

1. Ignition OFF, disconnect the high beam relay.
2. Ignition ON, verify that a test lamp does not illuminate between the relay switch controlled output circuit and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to voltage.

3. Verify that a test lamp illuminates between the relay switch B+ circuit and ground.

⇒

If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the relay switch controlled output circuit for a short to ground. If the circuit tests normal, test or replace the high beam relay.

4. Verify that a test lamp illuminates between the relay coil B+ circuit and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.

5. Disconnect the harness connector at the inoperative high beam headlamp.
6. Test for less than 1.0 ohm of resistance between the inoperative high beam headlamp ground circuit terminal B and ground.

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

7. Connect the harness connector at the inoperative high beam headlamp.
8. Connect a 20A fused jumper wire between the relay switch B+ circuit and the relay switch controlled output circuit. Verify the high beam headlamps are activated.

⇒	If the high beam headlamps do not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the inoperative high beam headlamp.

9. Connect a test lamp between the relay coil B+ circuit and the relay coil control circuit.
10. Command the high beam headlamps ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing 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.

11. If all circuits test normal, test or replace the high beam relay.

High Beam Indicator Malfunction

Ignition ON, with a scan tool perform the display test for the instrument panel cluster (IPC) and observe the high beam indicator.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

With the headlamp switch in the HEAD position, the headlamp switch headlamp ON signal circuit is grounded through the turn signal/multifunction switch at G300. In response to this input, the body control module (BCM) provides ground to either the headlamp low beam relay control circuit through the headlamp switch signal circuit or the headlamp high beam relay control circuit. The position of the headlamp dimmer switch determines which relay coil has ground. The BCM supplies ground to the relay coil circuits, if the headlamps are necessary. The LO BEAM and HI BEAM relays are supplied with battery positive voltage at there coil and switch input circuits. When the low beam relay coil is energized, current flows through the LH LOW and the RH LOW fuses to the low beam headlamps. When the headlamp high beam relay coil is energized, current flows through the LH HIGH and the RH HIGH fuses to the high beam headlamps. The headlights may be switched to high beam with the movement of the headlamp dimmer switch lever. With the headlamp dimmer switch in the high beam position the BCM sends a message via GMLAN to the instrument panel cluster (IPC) requesting the IPC to illuminate the high beam indicator. Ground for the left headlamp assembly is provided at G101. Ground for the right headlamp assembly is provided at G102. For more detailed information concerning headlamp operation refer to Exterior Lighting Systems Description and Operation .

Schematic Reference

Headlights/Daytime Running Lights (DRL) Schematics

Connector End View Reference

Lighting Systems Connector End Views

Electrical Information Reference

Scan Tool Reference

1. Ignition ON, observe the scan tool headlamp off switch parameter while turning the headlamp switch ON and OFF. The reading should toggle between INACTIVE and ACTIVE.

⇒	If the reading does not change between the commanded states, refer to Headlamp Switch Malfunction.

2. Observe the scan tool flash to pass switch parameter while applying and releasing the flash to pass switch. The reading should toggle between ACTIVE and INACTIVE.

⇒	If the reading does not change between the commanded states, refer to Headlamp Switch Malfunction.

3. Observe the scan tool high beam select switch parameter while applying and releasing the high beam select switch. The reading should toggle between ACTIVE and INACTIVE.

⇒	If the reading does not change between the commanded states, refer to Headlamp Switch Malfunction.

4. Observe the scan tool headlamp on switch parameter while turning the headlamp switch ON and OFF. The reading should toggle between ACTIVE and INACTIVE.

⇒	If the reading does not change between the commanded states, refer to Headlamp Switch Malfunction.

Headlamp Switch Malfunction

1. Ignition OFF, disconnect the C1 and C2 harness connectors at the turn signal/multifunction switch.
2. Test for less than 1.0 ohm of resistance between the ground circuit terminal 1 and ground.

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

3. Test for less than 1.0 ohm of resistance between the ground circuit terminal B and ground.

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

4. Ignition ON, verify the scan tool headlamp off switch parameter is INACTIVE.

⇒	If not the specified value, test the signal circuit terminal 4 for a short to ground. If the circuit tests normal, replace the BCM.

5. Verify the scan tool flash to pass 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.

6. Verify the scan tool high beam select switch parameter is INACTIVE.

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

7. Verify the scan tool headlamp on 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.

8. Install a 3A fused jumper wire between the signal circuit terminal 4 and ground. Verify the scan tool headlamp off 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.

9. Install a 3A fused jumper wire between the signal circuit terminal C 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 an open/high resistance. If the circuit tests normal, replace the BCM.

10. Install a 3A fused jumper wire between the signal circuit terminal D 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 an open/high resistance. If the circuit tests normal, replace the BCM.

11. Install a 3A fused jumper wire between the signal circuit terminal 2 and ground. Verify the scan tool headlamp on 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.

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

Headlamps Malfunction - Low Beam

1. Ignition OFF, disconnect the low beam relay.
2. Ignition ON, verify that a test lamp does not illuminate between the relay switch controlled output circuit and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to voltage.

3. Verify that a test lamp illuminates between the relay switch B+ circuit and ground.

⇒

If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the relay switch controlled output circuit for a short to ground. If the circuit tests normal, test or replace the low beam relay.

4. Verify that a test lamp illuminates between the relay coil B+ circuit and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.

5. Disconnect the harness connector at the inoperative low beam headlamp.
6. Test for less than 1.0 ohm of resistance between the inoperative low beam headlamp ground circuit terminal 2 and ground.

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

7. Connect the harness connector at the inoperative low beam headlamp.
8. Connect a 20A fused jumper wire between the relay switch B+ circuit and the relay switch controlled output circuit. Verify the low beam headlamps are activated.

⇒	If the low beam headlamps do not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the inoperative low beam headlamp.

9. Connect a test lamp between the relay coil B+ circuit and the relay coil control circuit.
10. Command the low beam headlamps ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing 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.

11. If all circuits test normal, test or replace the low beam relay.

Headlamps Malfunction - High Beam

1. Ignition OFF, disconnect the high beam relay.
2. Ignition ON, verify that a test lamp does not illuminate between the relay switch controlled output circuit and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to voltage.

3. Verify that a test lamp illuminates between the relay switch B+ circuit and ground.

⇒

If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the relay switch controlled output circuit for a short to ground. If the circuit tests normal, test or replace the high beam relay.

4. Verify that a test lamp illuminates between the relay coil B+ circuit and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.

5. Disconnect the harness connector at the inoperative high beam headlamp.
6. Test for less than 1.0 ohm of resistance between the inoperative high beam headlamp ground circuit terminal 2 and ground.

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

7. Connect the harness connector at the inoperative high beam headlamp.
8. Connect a 20A fused jumper wire between the relay switch B+ circuit and the relay switch controlled output circuit. Verify the high beam headlamps are activated.

⇒	If the high beam headlamps do not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the inoperative high beam headlamp.

9. Connect a test lamp between the relay coil B+ circuit and the relay coil control circuit.
10. Command the high beam headlamps ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing 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.

11. If all circuits test normal, test or replace the high beam relay.

High Beam Indicator Malfunction

Ignition ON, with a scan tool perform the display test for the instrument panel cluster (IPC) and observe the high beam indicator.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.