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.

Circuit/System Description

The headlamps may be turned ON 2 different ways. First, when the headlamp switch is placed in the headlamps position, for normal operation. Second, with the headlamp switch placed in the AUTO position, for automatic lamp control (ALC). During ALC, the headlamps will be in daytime running lamp (DRL) operation in daylight conditions, or headlamp operation in low light conditions. For headlamp operation, battery positive voltage is applied at all times to the coil and switch sides of the low or high beam relay in the underhood fuse block depending on the position of the headlamp dimmer switch. Ground to the headlamp switch is from G200. When the headlamp switch is placed in the HEAD position, ground is applied to the headlamp switch headlamps ON signal circuit of the body control module (BCM). When either the headlamp switch is placed in the headlamps position or ALC is enabled, the BCM applies a ground to the headlamp low or high beam relay control circuit. This energizes the relay and applies battery positive voltage to the left and right low or high beam fuses in the underhood fuse block, then through the headlamp supply voltage circuits to the headlamps. Ground is applied at all times to the left headlamp from G101 and to the right headlamp from G100. For high beam operation, the dimmer switch supplies a ground signal to the BCM. Ground to the headlamp dimmer switch is from G200. For flash-to-pass (FTP) operation, when the headlamp dimmer switch is placed in the FTP position, ground is applied from G200 through the headlamp dimmer switch to the FTP switch signal circuit to the BCM. The BCM then turns the high beam headlamps ON as long as the headlamp dimmer switch is held in the FTP position. If the headlight switch is left in the headlamps position, the inadvertent power control feature will turn OFF the headlights 10 minutes after the ignition switch is turned to the OFF position. If the driver places the headlight switch in the headlamps position after the ignition switch has been turned OFF, or if the ignition switch is in the ACCY position, the headlights will remain ON until turned OFF or the battery runs dead.

The normal headlamp switch operating position is AUTO, which enables the automatic lamp control (ALC). For ALC operation, the body control module (BCM) receives a signal from the ambient light sensor indicating a low or high ambient (outside) light level. The ambient light sensor is a light sensitive transistor that varies its voltage signal to the BCM in response to changes to the ambient light level. The BCM uses multiple inputs to determine daytime running lamp (DRL) or headlamp low/high beam operation. When the ignition key is turned to the RUN position the BCM determines the light/dark ambient light condition and activates the headlamps or DRL mode immediately. When a transition to the light/dark ambient light condition occurs after the ignition is in the RUN position there is an approximate 30-second delay in the headlamp/DRL transition. The ALC System also has a defeat feature and a wiper activated headlamps feature. To operate the ALC defeat, turn the headlamp switch counter clockwise one position past the AUTO position after starting the vehicle. This is a momentary switch position, and will return to the AUTO position. This action sends a temporary ground signal to the BCM requesting a change of states for the ALC. If the ALC is currently ON it will switch to OFF, and if the ALC is currently OFF it will reset the ALC to ON. The wiper activated headlamps feature is enabled anytime the ALC is enabled. When the front windshield wipers have been activated for approximately 30 seconds, and the ALC is in the DRL mode, the BCM will switch to headlamps ON.

The ambient light sensor is a light sensitive transistor that varies its signal to the body control module (BCM) in response to changes in the outside ambient light level. Any function or condition that turns ON the headlamps will cancel daytime running lamp (DRL) operation. With the headlamp switch in the OFF position, activating automatic lamp control (ALC), the front turn signal lamps will be turned ON after a 30-second delay under daylight conditions, which is determined by the ambient light sensor signal to the BCM. The DRL operates when the ignition switch is in the RUN position, the front wipers are not activated, and the transmission is not in PARK. When these conditions have been met and the ambient light sensor indicates daylight conditions, the BCM will illuminate the front turn signal lamps ON steady.

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 (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, expose the ambient light sensor to a bright incandescent lamp.
2. Wait 20 seconds.
3. Verify the DRL illuminate.

• If the DRL do not illuminate, Refer to DRL Inoperative.

4. Place the headlamp switch in the AUTO position.
5. Cover the ambient light sensor.
6. Wait 20 seconds.
7. Verify the headlamps illuminate.

• If the headlamps do not illuminate, Refer to ALC Inoperative.

8. Command the low beam headlamps ON and OFF with a scan tool. The low beam headlamps should turn ON and OFF when changing between the commanded states.

• If both low beam headlamps are inoperative, Refer to Low Beam Headlamps Inoperative.

• If only one low beam headlamp is inoperative, Refer to Headlamp Inoperative - One.

9. Command the high beam headlamps ON and OFF with a scan tool. The high beam headlamps should turn ON and OFF when changing between the commanded states.

• If both high beam headlamps are inoperative, Refer to Low Beam Headlamps Inoperative.

• If only one high beam headlamp is inoperative, Refer to Headlamp Inoperative - One.

10. Place the headlamp switch in the HEAD position.
11. Place the headlamp dimmer switch in the HI position. The high beam indicator should illuminate.

• If the high beam indicator does not illuminate, Refer to High Beam Indicator Inoperative.

12. Refer to Headlamp Switch Malfunction

Circuit/System Testing

DRL Inoperative
1. Disconnect the harness connector at the ambient light sensor.
2. Install a 3A fused jumper wire between the signal circuit terminal A and the low reference circuit terminal B.
3. Verify the scan tool Ambient Light Sensor parameter is 4-5 volts.

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

4. If all circuits test normal, replace the ambient light sensor.

ALC Inoperative
1. Disconnect the harness connector at the ambient light sensor.
2. Verify the scan tool Ambient Light Sensor parameter is less than 1 volt.

• If not 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. If all circuits test normal, replace the ambient light sensor.

Low Beam Headlamps Inoperative
1. Ignition OFF, disconnect the LO BEAM relay.
2. Ignition ON, verify that a test lamp illuminates between the relay switch B+ circuit and ground.

• If the test lamp does not illuminate, replace the underhood fuse block.

3. Connect a 10A fused jumper wire between the relay switch B+ circuit and the relay controlled output circuit. Verify the low beam headlamps are activated.

• If the low beam headlamps do not activate, test the low beam voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the underhood fuse block.

4. Ignition ON, verify that a test lamp illuminates between the relay coil B+ circuit and ground.

• If the test lamp does not illuminate, replace the underhood fuse block.

5. Connect a test lamp between the relay coil B+ circuit and the relay coil control circuit.
6. Command the low beam headlamps ON and OFF with a scan tool. The test lamp should illuminate when commanded ON.

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

• It the test lamp is always illuminated, test the relay coil control circuit for a short to ground. If the circuit tests normal, replace the BCM.

7. Replace the LO BEAM relay.

High Beam Headlamps Inoperative
1. Ignition OFF, disconnect the HI BEAM relay.
2. Ignition ON, verify that a test lamp illuminates between the relay switch B+ circuit and ground.

• If the test lamp does not illuminate, replace the underhood fuse block.

3. Connect a 10A fused jumper wire between the relay switch B+ circuit and the relay controlled output circuit. Verify the high beam headlamps are activated.

• If the high beam headlamps do not activate, replace the underhood fuse block.

4. Replace the HI BEAM relay.

Headlamp Switch Malfunction
1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Verify that a test lamp illuminates between the ground circuit terminal 4 and B+.

• If the test lamp does not illuminate, test the ground circuit terminal 4 for a short to voltage or an open/high resistance.

3. Ignition ON, install a 3A fused jumper wire between the signal circuit terminal 12 and ground. Verify the scan tool Headlamp On Switch parameter is Active.

• If not the specified value, test the signal circuit terminal 12 for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

4. Install a 3A fused jumper wire between the signal circuit terminal 10 and ground. Verify the scan tool Headlamp Off Switch parameter is Active.

• If not the specified value, test the signal circuit terminal 10 for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

5. Ignition OFF, disconnect the X2 harness connector at the turn signal/multifunction switch.
6. Verify that a test lamp illuminates between the ground circuit terminal D and B+.

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

7. Ignition ON, 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 terminal A for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

8. 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 terminal E for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

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

Headlamp Inoperative - One
1. Place the headlamp switch in the ON position of the inoperative lamp.
2. Disconnect the harness connector of the inoperative lamp.
3. Verify that a test lamp illuminates between the ground circuit terminal B and B+.

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

4. Test the voltage supply circuit terminal A for a short to ground or an open/high resistance.

High Beam Indicator Inoperative
1. Command the instrument panel Display Test ON with a scan tool. The high beam indicator should illuminate.

• If the high beam indicator does not illuminate, replace the instrument panel cluster.

2. If all circuits test normal, replace the BCM.

Repair Instructions

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

* Control Module References (Programming and Relearning)
* 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)
* Instrument Cluster Replacement (Service and Repair)
* Headlamp Switch Replacement (Service and Repair)