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 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 body control module (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 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.
Reference Information
Schematic Reference
Headlights/Daytime Running Lights (DRL) Schematics (Headlights/Daytime Running Lights (DRL) Schematic)
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 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 and the low reference circuit.
3. Verify the scan tool Day/Night Status parameter is Day.
• 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 Day/Night Status parameter is Night.
• 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, replace the underhood fuse block.
4. 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 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 (Verification Tests) after completing the diagnostic procedure.
* Ambient Light Sensor Replacement (Service and Repair)
* Instrument Cluster Replacement (Instrument Cluster Replacement)
* 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)
* Underhood Electrical Center or Junction Block Replacement (LAT) ()Underhood Electrical Center or Junction Block Replacement (LY7, LZ4) ()
* Control Module References (Programming and Relearning) for BCM replacement, setup, and programming