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Headlamps Malfunction



Headlamps Malfunction

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.



Diagnostic Fault Information






Circuit/System Description

With the headlamp switch in the ON position, the headlamp switch headlamp ON signal circuit is grounded through the turn signal/multifunction switch at G200. In response to this input, the instrument panel module (IPM) provides ground to either the headlamp low beam relay control circuit or the headlamp high beam relay control circuit. The position of the headlamp dimmer switch determines which relay coil has ground. The IPM supplies ground to the relay coil circuits, if the headlamps are necessary. The underhood fuse block supplies battery positive voltage to both relay switch circuits. When the low beam relay coil is energized, current flows through the LT LOW BEAM and the RT LOW BEAM fuses to the low beam headlamps. The low beam headlamps are grounded at G104. When the headlamp high beam relay coil is energized, current flows through the LT HI BEAM and the RT HI BEAM fuses to the high beam headlamps. The high beam headlamps are also grounded at G104. With the headlamp dimmer switch in the high beam position the IPM sends a message via GMLAN serial data to the instrument panel cluster (IPC) requesting the IPC to illuminate the high beam indicator.


Reference Information
Schematic Reference

* Headlights/Daytime Running Lights (DRL) Schematics (Headlights/Daytime Running Lights (DRL) Schematics)
* Inside Rearview Mirror Schematics (Inside Rearview Mirror Schematics)

Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Exterior Lighting Systems Description and Operation (Exterior Lighting Systems Description and Operation)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning)


Circuit/System Verification

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

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

2. Observe the scan tool headlamp/park lamp off switch parameter while turning the headlamp switch from the PARK and HEAD positions to the OFF position. The reading should toggle between ON and OFF.

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

3. 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.

4. 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.




Circuit/System Testing


Headlamp Switch Malfunction
1. Ignition OFF, disconnect the X3 and X4 harness connectors at the turn signal/multifunction switch.
2. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit terminal K.

• If the test lamp does not illuminate, test the ground circuit for an open/high resistance.

3. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit terminal B.

• If the test lamp does not illuminate, test the ground circuit for an open/high resistance.

4. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit terminal D.

• If the test lamp does not illuminate, test the ground circuit for an open/high resistance.

5. Ignition ON, verify the scan tool headlamp switch parameter is OFF.

• If not the specified value, test the signal circuits at terminal N and terminal L for shorts to ground. If the circuits test normal, replace the IPM.

6. Verify the scan tool flash to pass switch parameter is INACTIVE.

• If not the specified value, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the IPM.

7. Verify the scan tool high beam select 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 IPM.

8. Install a 3A fused jumper wire between the signal circuit terminal N and ground. Verify the scan tool headlamp switch parameter is ON.

• 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 IPM.

9. Install a 3A fused jumper wire between the signal circuit terminal L and ground. Verify the scan tool headlamp switch parameter is ON.

• 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 IPM.

10. Install a 3A fused jumper wire between the signal circuit terminal A 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 IPM.

11. Install a 3A fused jumper wire between the signal circuit terminal E 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 IPM.

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 control circuit terminal R25 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 B+ circuit terminal R24 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 control circuit terminal R25 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 B+ circuit terminal R26 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. Ignition OFF, scan tool OFF, exterior lamps OFF, test for less than 5.0 ohms between the inoperative low 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 low beam headlamp.
8. Connect a 40A fused jumper wire between the B+ circuit terminal R24 and the control circuit terminal R25. 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 B+ circuit terminal R26 and the control circuit terminal R23.
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 IPM.


• 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 IPM.

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



Headlamps Malfunction - High Beam (Standard)
1. Ignition OFF, disconnect the high beam relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal R29 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 B+ circuit terminal R28 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 control circuit terminal R29 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 B+ circuit terminal R30 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. Ignition OFF, scan tool OFF, exterior lamps OFF, test for less than 5.0 ohms 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 B+ circuit terminal R28 and the control circuit terminal R29. 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 B+ circuit terminal R30 and the control circuit terminal R27.
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 IPM.


• 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 IPM.

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



Headlamps Malfunction - High Beam (Intellibeam)
1. Ignition ON, activate the intellibeam feature and observe the intellibeam indicator located on the inside rearview mirror (ISRVM). The indicator should flash 1 time to indicate the system has been activated.

• If the indicator flashes more than 3 times, replace the ISRVM.

2. Ignition OFF, disconnect the harness connector at the inside rearview mirror (ISRVM).
3. Connect a test lamp between B+ and the relay control circuit terminal 3.
4. 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 IPM.


• 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 IPM.

5. Connect a test lamp between B+ and the high beam DIM enable circuit terminal 4.
6. Ignition ON, verify the test lamp illuminates with the sunload sensor covered and the headlamp switch in the AUTO position.

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


• 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 IPM.

7. Ignition OFF, disconnect the harness connector at the automatic headlamp dimming relay.
8. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.

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

9. Ignition OFF, scan tool OFF, exterior lamps OFF, test for less than 5.0 ohms between the automatic headlamp dimming relay ground circuit terminal 85 and ground.

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

10. Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

11. Disconnect the harness connector at the inoperative high beam headlamp.
12. Ignition OFF, scan tool OFF, exterior lamps OFF, test for less than 5.0 ohms 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.

13. Connect the harness connector at the inoperative high beam headlamp.
14. Connect a 10A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the high beam headlamps are activated.

• If the high beam headlamps do not illuminate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the inoperative high beam headlamp.


• If the high beam headlamps illuminate, test the automatic high beam PWM signal circuit terminal 86 for a short to voltage, short to ground or an open/high resistance. If the circuit tests normal, replace the ISRVM.

15. If all circuits test normal, test or replace the automatic headlamp dimming relay.


High Beam Indicator Malfunction (Standard)

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

If the high beam indicator does not illuminate during the test or remains illuminated at all times, replace the IPC.


If the high beam indicator illuminates during the test, replace the IPM.



High Beam Indicator Malfunction (Intellibeam)
1. Ignition ON, with a scan tool perform the display test for the instrument panel cluster (IPC) and observe the high beam indicator. The high beam indicator should illuminate during the test and then turn OFF.

• If the high beam indicator does not illuminate or remains illuminated at all times, replace the IPC.

2. Ignition ON, place the headlamp dimmer switch in the high beam position and observe the high beam indicator. The indicator should illuminate.

• If the high beam indicator does not illuminate , replace the IPM.

3. Ignition OFF, disconnect the harness connector at the inside rearview mirror (ISRVM).
4. Test the automatic high beam DIM status circuit for a short to voltage, short to ground, or an open/high resistance. If the circuit tests normal, replace the ISRVM.



Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Headlamp Bulb Replacement (Hi Beam) (Service and Repair)Headlamp Bulb Replacement (Lo Beam) (Service and Repair)
* Underhood Electrical Center or Junction Block Replacement (Service and Repair)
* Relay Replacement (Attached to Wire Harness) (Relay Replacement (Attached to Wire Harness))Relay Replacement (Within an Electrical Center) (Relay Replacement (Within an Electrical Center))
* Turn Signal Multifunction Switch Replacement (Turn Signal Multifunction Switch Replacement)
* Control Module References (Programming and Relearning) for IPM, IPC, or ISRVM replacement, setup, and programming


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