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Home >> Hummer >> 2008 >> H3 L5-3.7L >> Repair and Diagnosis >> Lighting and Horns >> Testing and Inspection >> Symptom Related Diagnostic Procedures >> Headlamps Malfunction

Headlamps Malfunction



Headlamps Malfunction

Diagnostic Instructions

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



Diagnostic Fault Information






Circuit/System Description

The ambient light sensor is a light sensitive transistor that varies its voltage signal to the body control module (BCM) in response to changes to the outside (ambient) light level. When the BCM receives this signal, it will either turn ON the daytime running lamps (DRL) or the headlamps for auto headlamp operation. Any function or condition that turns ON the headlights will cancel the DRL operation. With the headlight switch in the AUTO position, the headlights will either be turned ON or OFF, after an approximate 8 second delay depending on whether daylight or low light conditions are sensed. When the ambient light sensor signals the BCM for DRL operation in daylight conditions, the BCM illuminates the low beam headlamps at a reduced intensity utilizing the DRL relay. The DRL will operate when the ignition switch is in the RUN position, the headlamp and panel dimmer switch is in the AUTO position, the gear selector is not in the PARK position, and the parking brake is released. When these conditions have been met and the ambient light sensor indicates daytime conditions, the DRL will illuminate.


Reference Information
Schematic Reference

Headlights/Daytime Running Lights (DRL) Schematics (Headlights/Daytime Running Lights (DRL) Schematics)
Connector End View Reference

Component Connector End Views (Component Connector End 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) for scan tool information


Circuit/System Verification

1. Ignition ON, observe the scan tool Headlamp Off Switch parameter while cycling the headlamp switch between the Auto and Off positions. The parameter should cycle between Active while in the Off position and Inactive when released.

• If the parameter does not cycle between the specified values, refer to Headlamp Switch Circuit Test.

2. Observe the scan tool Headlamp On Switch parameter while cycling the headlamp switch between the Auto and Head position. The parameter should cycle between Active and Inactive.

• If the parameter does not cycle between the specified values, refer to Headlamp Switch Circuit Test.

3. 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 parameter should cycle between Active and Inactive.

• If the parameter does not cycle between the specified values, refer to Turn Signal/Multifunction Switch Circuit Test.

4. Command the Headlamps ON and OFF with a scan tool. Verify the low beam headlamps turn ON and OFF.

• If the low beam headlamps do not cycle between the commanded states, refer to Low Beam Headlamp Circuit Test.

5. Command the High Beams ON and OFF with a scan tool. Verify the high beam headlamps turn ON and OFF.

• If the high beam headlamps do not cycle between the commanded states, refer to High Beam Headlamp Circuit Test.

6. Command the FLASH TO PASS On and Off at the Turn Signal/Multifunction Switch. Verify that the High Beam Headlamps turn On and Off between the commanded states.

• If the high beam headlamps do not cycle between the commanded states, refer to the Headlamp Flash to Pass Inoperative Circuit Test.

7. Ignition ON, turn the headlamp dimmer switch to the high beam position and observe the headlamps and the IPC high beam indicator. The high beam headlamps and the high beam indicator should illuminate.



Circuit/System Testing


Headlamp Switch Circuit Test
1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Verify that a test lamp illuminates between the ground circuit terminal 3 and B+.

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

3. Ignition ON, verify the scan tool Headlamp On 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.

4. Verify the scan tool Headlamp Off Switch parameter is Inactive.

• If not the specified value, test the signal circuit terminal 5 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 4 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 and open/high resistance. If the circuit tests normal, replace the BCM.

6. Install a 3A fused jumper wire between the signal circuit terminal 5 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 and open/high resistance. If the circuit tests normal, replace the BCM.

7. If all circuits test normal, test or replace the headlamp switch.



Turn Signal/Multifunction Switch Circuit Test
1. Ignition OFF, disconnect the X201 harness connector at the turn signal/multifunction switch.
2. Verify that a test lamp illuminates between the ground circuit terminal B10 and B+.

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

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

• If not the specified value, test the signal circuit terminal A11 for a short to ground. If the circuit tests normal, replace the BCM.

4. Install a 3A fused jumper wire between the signal circuit terminal A11 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.

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



Low Beam Headlamp Circuit Test
1. Ignition OFF, disconnect the HDLP relay.
2. Ignition ON, verify that a test lamp does not illuminate between the relay control circuit terminal 86 and B+.

• If the test lamp illuminates, test the relay control circuit for a short to ground. If the circuit tests normal, replace the BCM.

3. Verify that the test lamp illuminates when the scan tool Headlamps On Switch parameter is Active.

• If the test lamp does not illuminate, test the relay control circuit for an open/high resistance. If the circuit tests normal, replace the BCM.

4. Disconnect the HI/LO BEAM relay.
5. Verify that a test lamp illuminates between the relay ground circuit terminal 30 and B+.

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

6. Ignition ON, verify that a test lamp does not illuminate between the relay control circuit terminal 86 and ground.

• If the test lamp illuminates, test the relay control circuit for a short to voltage. If the circuit tests normal, replace the BCM.

7. Install the HDLP and HI/LO BEAM relays.
8. Disconnect the appropriate headlamp bulb.
9. Ignition ON, verify that a test lamp illuminates between the low beam control circuit terminal A and B+.

• If the test lamp does not illuminate, test the control circuit for an open/high resistance. If the circuit tests normal, replace the HI/LO BEAM relay.

10. Connect a test lamp between the affected headlamp control circuit terminal B and ground.
11. Verify that the test lamp illuminates when the scan tool Headlamps control is commanded ON.

• If the test lamp does not illuminate, test the control circuit for a short to ground or open/high resistance. If the circuit tests normal replace the HDLP relay.

12. If all the circuits test normal, replace the headlamp bulb.



High Beam Headlamp Circuit Test
1. Ignition OFF, disconnect the HI/LO BEAM relay.
2. Ignition ON, verify that a test lamp illuminates between the HI/LO BEAM relay control circuit terminal 86 and ground when the scan tool High Beams control is commanded ON.

• If the test lamp does not illuminate, test the control circuit for a short to ground or open/high resistance. If the circuit tests normal, replace the BCM.

3. Install the HI/LO BEAM relay.
4. Disconnect the appropriate headlamp bulb.
5. Connect a test lamp between the high beam control circuit terminal C and B+.
6. Ignition ON, verify that the test lamp illuminates when the scan tool High Beam Select Switch control is commanded Active.

• If the test lamp does not illuminate, test the control circuit for an open/high resistance. If the circuit tests normal, replace the HI/LO BEAM relay.

7. If all the circuits test normal, replace the appropriate headlamp bulb.



Headlamp Flash to Pass Inoperative
1. Ignition OFF, disconnect the HI/LO BEAM relay.
2. Ignition ON, verify that a test lamp illuminates between the HI/LO BEAM relay control circuit terminal 86 and ground when the scan tool High Beams control is commanded ON.

• If the test lamp does not illuminate, test the control circuit for a short to ground or open/high resistance. If the circuit tests normal, replace the BCM.

3. Install the HI/LO BEAM relay.
4. Ignition OFF, disconnect the X201 harness connector at the Turn SIgnal/Multifunction Switch.
5. Ignition ON, headlamps ON, FLASH TO PASS switch active, connect a test lamp between the control circuit terminal A10 and B+.
6. Verify that a test lamp illuminates when the FLASH TO PASS switch is active.

• If the test lamp does not illuminate, test the control circuit for an open/high resistance. If the circuit tests normal, replace the Turn SIgnal/Multifunction Switch.

7. Ignition OFF, reconnect the X201 harness connector at the Turn SIgnal/Multifunction Switch.
8. Disconnect the appropriate headlamp bulb.
9. Connect a test lamp between the high beam control circuit terminal C and B+.
10. Ignition ON, verify that the test lamp illuminates when the Turn Signal/Multifunctional Switch FLASH TO PASS operation is commanded ON.

• If the test lamp does not illuminate, test the control circuit for an open/high resistance. If the circuit tests normal, replace the HI/LO BEAM relay.

11. If all the circuits test normal, replace the appropriate headlamp bulb.



Headlamp Indicator Malfunction

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 BCM.



Repair Instructions

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

* Ambient Light Sensor Replacement (Service and Repair)
* Headlamp Switch Replacement (Service and Repair)
* Turn Signal Multifunction Switch Replacement (Turn Signal Multifunction Switch Replacement)
* Headlamp Bulb Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for BCM replacement, programming, and setup


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