Headlamps Malfunction

Headlamps Malfunction

Diagnostic Instructions

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

Circuit/System Description

The headlamps may be turned ON 2 different ways. First, when the driver places the headlamp switch in the HEADLAMP 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 OFF in daylight conditions, or low beam operation in low light conditions. Battery positive voltage is supplied to the low beam relay and the high beam relay in the underhood fuse block. When low beam headlamps are requested, the body control module (BCM) supplies ground to the coil side of the low beam relay. This activates the relay and the relay supplies voltage to the left hand low beam headlamp through the LH LOW BEAM fuse and to the right hand low beam headlamp through the RH LOW BEAM fuse. Ground for the left hand low beam headlamp is provided at G101. Ground for the right hand low beam headlamp is provided at G102. When high beam headlamps are requested, the BCM supplies ground to the coil side of the high beam relay. This activates the relay and the relay supplies voltage to the left hand high beam headlamp through the LH HIGH BEAM fuse and to the right hand high beam headlamp through the RH HIGH BEAM fuse. Ground for the left hand high beam headlamp is provided at G101. Ground for the right hand high beam headlamp is provided at G102.

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 headlights if the headlamp switch is in the AUTO position. 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 30 second delay depending on whether daylight or low light conditions are sensed. The DRL illuminates the park/turn signal and DRL lamps. The DRL will operate when the ignition switch is in the ON 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. DRL operation in manual transmission equipped vehicles will occur when the ignition switch is in the ON position, and the parking brake is released.

Circuit/System Verification

1. Ignition ON, expose the ambient light sensor to a bright incandescent lamp.
2. Wait 20 seconds.
3. Verify the scan tool Day/Night Status parameter is Day.

^ If not the specified value, 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 scan tool Day/Night Status parameter is Night.

^ If not the specified value, 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 Day/Night Status parameter is Day.

^ If not the specified value, test the low reference circuit terminal B 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 Day/Night Status parameter is Night.

^ If not the specified value, test the signal circuit terminal A 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 X2 harness connector at the turn signal/multifunction switch.
2. Install a 3A fused jumper wire between the LOW BEAM relay control circuit terminal E and ground. Verify the low beam headlamps illuminate.

^ If the low beam headlamps do not illuminate, test the relay control circuit terminal E for a short to voltage or an open/high resistance. If the circuit tests normal, replace the underhood fuse block.

High Beam Headlamps Inoperative
1. Ignition OFF, disconnect the X1 harness connector at the BCM.
2. Install a 3A fused jumper wire between the HI BEAM relay control circuit terminal 44 and ground. Verify the high beam headlamps illuminate.

^ If the high beam headlamps do not illuminate, test the relay control circuit terminal 44 for a short to voltage or an open/high resistance. If the circuit tests normal, replace the underhood fuse block.

Headlamp Switch Malfunction
1. Ignition OFF, disconnect the X1 harness connector at the turn signal/multifunction switch.
2. Verify that a test lamp illuminates between the ground circuit terminal 1 and B+.

^ If the test lamp does not illuminate, test the ground circuit terminal 1 for a short to voltage or an open/high resistance.

3. Ignition ON, install a 3A fused jumper wire between the signal circuit terminal 2 and ground. Verify the scan tool Headlamp On Switch parameter is Active.

^ If not the specified value, test the signal circuit terminal 2 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 4 and ground. Verify the scan tool Headlamp Off Switch parameter is Active.

^ If not the specified value, test the signal circuit terminal 4 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 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.

7. Ignition ON, install a 3A fused jumper wire between the signal circuit terminal C and ground. Verify the scan tool Flash to Pass Switch parameter is Active.

^ If not the specified value, test the signal circuit terminal C 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 D and ground. Verify the scan tool High Beam Select Switch parameter is Active.

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

9. Install a 10A fused jumper wire between the signal circuit terminal F and ground. Verify the low beam headlamps are activated.

^ If the low beam headlamps do not activate, test the signal circuit terminal F for a short to voltage or an open/high resistance.

10. If all circuits test normal, replace the 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 after completing the diagnostic procedure. Verification Tests

* Underhood Electrical Center or Junction Block Bracket Replacement
* Turn Signal Multifunction Switch Replacement
* Ambient Light Sensor Replacement
* Instrument Cluster Replacement