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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 (Connector Views)
Description and Operation

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

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

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 turning the headlamp switch between the OFF, AUTO and PARK positions. The parameter should cycle between Active and Inactive.

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

2. Observe the scan tool Headlamp ON Switch parameter while turning the headlamp switch between the OFF, AUTO and PARK positions. The parameter should cycle between Active and Inactive.

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

3. With the headlamps ON, observe the scan tool High Beam Select Switch parameter while switching the turn signal/multifunction switch between the low and high beam positions. The parameter should toggle between Active and Inactive.

• If the reading does not change between the selected states, refer to Turn Signal/Multifunction Switch Malfunction.

4. Observe the scan tool High Beam Select Switch parameter while switching the flash to pass switch between the ON and OFF positions. The parameter should toggle between Active and Inactive.

• If the reading does not change between the selected states, refer to Turn Signal/Multifunction Switch Malfunction.

5. Command the Headlamps 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 when commanded, refer to Headlamps Malfunction - Low Beam.

6. Command 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 when commanded, refer to Headlamps Malfunction - High Beam.

7. Command the Lamp Test ON and OFF with a scan tool. The high beam indicator should turn ON and OFF when changing between the commanded states.

• If the high beam indicator illuminates during the test, replace the BCM.
• If the high beam indicator does not illuminate during the test or remains illuminated at all times, replace the instrument cluster.

Circuit/System Testing

Headlamp Switch Malfunction
1. Ignition OFF, disconnect the harness connector at the headlamp and panel dimmer switch.
2. Verify that a test lamp illuminates between the low reference 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 3 A 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 3 A 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 and panel dimmer switch.

Turn Signal/Multifunction Switch Malfunction
1. Ignition OFF, disconnect the harness connector at the turn signal/multifunction switch.
2. Test for less than 5 ohm between the ground circuit terminal and ground.

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

3. Ignition ON, headlamps ON, verify the scan tool Headlamp ON switch parameter is Active.

• If not the specified value, test the signal circuit terminal 3 for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

4. 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.

5. Install a 3 A fused jumper wire between the signal circuit terminal A10 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.

6. Install a 3 A 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 an 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 HDLP relay.
2. Verify that a test lamp does not illuminate between the control circuit terminal 30 and ground.

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

3. Verify that a test lamp illuminates at the B+ circuit terminal 86 and ground.

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

4. Verify that a test lamp illuminates at the B+ circuit terminal 87 and ground.

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

5. Install a 10 A fused jumper wire between the B+ circuit terminal 87 and the control circuit terminal 30. The low beam headlamps should illuminate.

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

6. Connect a test lamp between the relay control circuit terminal 85 and the B+ circuit terminal 86. Command the Headlamps 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 relay control circuit for a short to ground. If the circuit tests normal, replace the BCM.
• If the test lamp is always OFF, test the relay control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

7. Ignition OFF, disconnect the harness connector at the appropriate headlamp.
8. Test for less than 5.0 ohm between the ground circuit terminal B and ground.

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

9. Connect a test lamp between the control circuit terminal A and ground.
10. Ignition ON, command the Headlamps ON and OFF with a scan tool. The test should turn ON and OFF.

• If the test lamp is always ON, test the control circuit for a short to voltage.
• If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance.

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

Headlamp Malfunction - High Beam
1. Ignition OFF, disconnect the BEAM SEL relay.
2. Ignition ON, verify that a test lamp illuminates between the control circuit terminal 87 and ground.

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

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

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

4. Verify a test lamp illuminates between the ground circuit terminal 85 and B+.

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

5. Connect a test lamp between the relay control circuit terminal 86 and ground. Command the High Beams 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 relay control circuit for a short to ground. If the circuit tests normal, replace the BCM.
• If the test lamp is always OFF, test the relay control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

6. Ignition OFF, disconnect the harness connector at the appropriate high beam headlamp.
7. Connect a test lamp between the ground circuit terminal B and B+.
8. Ignition ON, high beams ON, the test lamp should illuminate.

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

9. Ignition OFF, connect a test lamp between the control circuit terminal A and ground.
10. Ignition ON, command the Headlamps ON and OFF with a scan tool. The test should turn ON and OFF.

• If the test lamp is always ON, test the control circuit for a short to voltage.
• If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance.

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

Repair Instructions

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

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

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