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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 Instructionsprovides 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. In response to this input, the body control module (BCM) 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 is supplied with ground. The BCM supplies ground to the relay coil circuits, if the headlamps are necessary. The underhood fuse block supplies battery positive voltage to the relay coil and switch circuits. The low beam headlamps operate when the BCM grounds the relay coil control circuit to the relay coil of the low beam headlamp relay. This energizes the low beam relay causing the switch contacts to close. With the switch contacts closed, battery voltage is applied to the LT LO and RT LO beam fuses through to the left and right light emitting diode (LED) control modules. When the headlamp high beam relay coil is energized, current flows through the LT HI BEAM and the RT HI BEAM fuses to the left and right LED control modules. With the headlamp dimmer switch in the high beam position the BCM sends a serial data message to the instrument panel cluster (IPC) requesting the IPC to illuminate the high beam indicator.

Diagnostic Aids

The headlamp outage detection circuits are low current B+ circuits supplied by the BCM. For purposes of testing, a test lamp connected between the outage detection circuit and ground will not illuminate due to low current.

Reference Information
Schematic Reference

* Headlights/Daytime Running Lights (DRL) Schematics
* Exterior Lights Schematics Exterior Lights Schematics

Connector End View Reference

Component Connector End Views Connector End Views By Name
Description and Operation

Exterior Lighting Systems Description and Operation Exterior Lighting Systems
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 Relearningfor scan tool information

Circuit/System Verification

1. Ignition ON, observe the scan tool Headlamp Switch parameter while turning the headlamp switch ON and OFF. The reading should change between Active and Inactive.

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

2. Observe the scan tool Auto Hdlp. Disable Sw. 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 specified values, refer to Headlamp Switch Malfunction.

3. Observe the scan tool Flash to Pass Switch parameter while applying and releasing the turn signal/multifunction switch. The reading should toggle between Active and Inactive.

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

5. Command the Low Beams ON and OFF with a scan tool. The low beam headlamps should turn ON and OFF when commanded.

• 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 commanded.

• If the high beam headlamps do not turn ON and OFF when commanded, refer to Headlamps Malfunction - High Beam.

7. Observe the low beam, high beam, park and marker lamp LEDs at each headlamp assembly. All LEDs should illuminate when commanded ON

• If all LEDs illuminate when commanded and the Service Headlamp Assembly indicator is ON, refer to Headlamp Outage Detection Malfunction.

8. Command the Lamp Test ON and OFF with a scan tool. The lights on indicator, high beam indicator and service headlamp assembly indicator should turn ON and OFF when changing between the commanded states.

• If the lights on indicator, high beam indicator and service headlamp assembly indicator illuminate during the test, replace the BCM.
• If the lights on indicator, high beam indicator and service headlamp assembly indicator do not illuminate during the test or remain 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. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit terminal 8.

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

3. Ignition ON, verify the scan tool Headlamp 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.

4. 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.

5. Install a 3 A fused jumper wire 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 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 3 and ground. Verify the scan tool Auto Hdlp. Disable Sw. 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 X2 harness connector at the turn signal/multifunction switch.
2. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit terminal D.

• 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 A for a short to ground. 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 E 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 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 BCM.

6. Install a 3 A 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 BCM.

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

Headlamps Malfunction - Low Beam
1. Ignition OFF, disconnect the HDLP LO/HID relay.
2. 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.

3. Verify that a test lamp illuminates between the B+ circuit terminal 85 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 between the B+ circuit terminal 30 and ground.

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

5. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
6. Command the Low 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 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.

7. Ignition OFF, connect the HDLP LO/HID relay.
8. Disconnect the harness connector at the appropriate headlamp.
9. Ignition OFF, scan tool OFF, exterior lamps OFF, test for less than 5.0 ohm between each ground circuit terminal listed below and ground.

* Ground circuit terminal F
* Ground circuit terminal M

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

10. Connect a test lamp between the control circuit terminal A and ground.
11. Command the Low 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 control circuit for a short to voltage. If the circuit tests normal, replace the HDLP LO/HID relay.
• 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 HDLP LO/HID relay.

12. Ignition OFF, connect the harness connector at the headlamp.
13. Command the Low Beams ON and OFF with a scan tool. The low beam headlamp should turn ON and OFF when changing between the commanded states.

Note: Swap the control module from the other headlamp to test.

• If any low beam LEDs do not illuminate, replace the headlamp control module.
• If some of the low beam LEDs still do not illuminate, replace the headlamp assembly.

Headlamps Malfunction - High Beam
1. Ignition OFF, disconnect the X4 connector at the underhood fuse block.
2. Connect a test lamp between the control circuit terminal C3 and B+.
3. Ignition ON, 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 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, disconnect the harness connector at the appropriate headlamp.
5. Ignition OFF, scan tool OFF, exterior lamps OFF, test for less than 5.0 ohm between each ground circuit terminal listed below and ground.

* Ground circuit terminal F
* Ground circuit terminal M

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

6. Connect a test lamp between the control circuit terminal L and ground.
7. 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 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.

8. Ignition OFF, connect the harness connector at the headlamp.
9. Command the High Beams ON and OFF with a scan tool. The high beam headlamp should turn ON and OFF when changing between the commanded states.

Note: Swap the control module from the other headlamp to test.

• If any high beam LEDs do not illuminate, replace the headlamp control module.
• If some of the high beam LEDs still do not illuminate, replace the headlamp assembly.

Headlamp Outage Detection Malfunction
1. Ignition OFF, disconnect the harness connector at the appropriate headlamp assembly.
2. Ignition ON, test for B+ between the signal circuit terminal C and ground.

• If less than the specified value, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

3. Ignition ON, verify that a test lamp does not illuminate between the signal circuit terminal C and ground.

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

4. If all circuits test normal, test or replace the headlamp control module.

Repair Instructions

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

* Headlamp Replacement
* Headlamp Control Module Replacement Headlamp Control Module Replacement
* Headlamp Ballast Replacement Headlamp Ballast Replacement
* Headlamp Switch Replacement
* Relay Replacement
* Turn Signal Multifunction Switch Replacement Turn Signal Multifunction Switch Replacement
* Underhood Electrical Center or Junction Block Replacement Underhood Electrical Center or Junction Block Replacement
* Control Module References Programming and Relearningfor BCM, instrument panel or headlamp control module replacement, setup, and programming

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