Daytime Running Lamps Malfunction
Daytime Running Lamps 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.
Diagnostic Fault Information
Circuit/System Description
The ambient light sensor is a light sensitive transistor that varies the voltage signal to the body control module (BCM) based on outside lighting conditions. When the ambient light sensor indicates daytime conditions with engine running, the body control module (BCM) grounds the DRL relay control circuit, energizing the DRL relay. With the DRL relay energized, voltage is applied through the relay switch contacts, the DRL 1 fuse, and the DRL 2 fuse to the left and right low beam headlamps. Any function or condition that turns the headlamps ON will cancel DRL operation.
Circuit/System Verification
1. Turn the headlamp switch to the headlamps ON position, the low beam headlamps should illuminate.
^ If the low beam headlamps do not illuminate, refer to Headlamps Malfunction. Headlamps Malfunction
2. Headlamps OFF, command the DRL ON with a scan tool. The DRLs should illuminate.
^ If the DRLs do not illuminate, refer to Circuit/System Testing.
3. Ignition ON, carefully supply sufficient light to simulate daylight conditions to the ambient light sensor for more than 30 seconds. Observe the scan tool Ambient Light Status parameter. The reading should be Day.
^ If not the specified value, refer to the Ambient Light Sensor Test.
Circuit/System Testing
Ignition ON and headlamps OFF, with a test lamp connected to ground, probe each of the test points on the DRL 1 fuse while commanding the DRL ON and OFF with a scan tool. The test lamp should illuminate at one or both of the fuse test points.
If the test lamp does not illuminate at either test point, refer to DRL Relay Test.
If the test lamp illuminates, refer to DRL Circuit Test.
DRL Relay Test
1. Ignition OFF, disconnect the X4 harness connector at the BCM.
2. Ignition ON, test for B+ between the control circuit terminal 23 and ground.
^ If less than the specified value, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal replace the underhood fuse block.
3. Install a 3A fused jumper wire between the control circuit terminal 23 and ground. The daytime running lamps should illuminate.
^ If the daytime running lamps do not illuminate and/or the jumper wire fuse opened, test the control circuit for a short to voltage. If the circuit tests normal, replace the underhood fuse block.
4. If all circuits test normal, replace the BCM.
DRL Circuit Test
1. Ignition ON and the headlamps OFF.
2. With a test lamp connected to ground, probe each of the test points on the DRL 2 fuse while commanding the DRL ON and OFF with a scan tool. The test lamp should turn ON and OFF between commanded states at one or both of the fuse test points.
^ If the test lamp is always ON, test the control circuit between the DRL 1 fuse and the DRL 2 fuse 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 between the DRL 1 fuse and the DRL 2 fuse for a short to ground or an open/high resistance. If the circuit tests normal, replace the underhood fuse block.
Ambient Light Sensor Test
1. Ignition OFF, disconnect the harness connector at the ambient light sensor.
2. Ignition OFF, test for less than 5.0 ohms between the ground circuit terminal B and ground.
^ If greater than the specified range, test the ground circuit for an open/high resistance.
3. Ignition ON, verify the scan tool Ambient Light Sensor parameter is greater than 4.65 volts.
^ If less than the specified range, test the signal circuit terminal A or a short to ground. If the circuit tests normal, replace the BCM
4. Install a 3A fused jumper wire between the signal circuit terminal A and ground. Verify the scan tool Ambient Light Sensor parameter is less than 1.96 volt.
^ If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
5. If all circuits test normal, test or replace the ambient light sensor.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests
* Accessory Wiring Junction Block Replacement.