Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | 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 | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
DRL Ambient Light Sensor Signal | B2645 03 | B2645 07 | B2645 07 | -- |
DRL Ambient Light Sensor Low Reference | -- | B2645 07 | -- | -- |
Left Headlamp Low Beam Voltage Supply | 1, 3 | 1, 3 | 4 | -- |
Right Headlamp Low Beam Voltage Supply | 1, 3 | 1, 3 | 4 | -- |
DRL Relay Control | 2 | 1 | B2600 00 | -- |
Left Headlamp Low Beam Ground | -- | 3 | -- | -- |
Right Headlamp Low Beam Ground | -- | 3 | -- | -- |
| ||||
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.
Reference Information
Schematic Reference
Headlights/Daytime Running Lights (DRL) Schematics
Connector End View Reference
Lighting Systems Connector End Views
Electrical Information Reference
Scan Tool Reference
Circuit/System Verification
- Turn the headlamp switch to the headlamps ON position, the low beam headlamps should illuminate.
- Headlamps OFF, command the DRL ON with a scan tool. The DRLs should illuminate.
- 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 the low beam headlamps do not illuminate, refer to Headlamps Malfunction . |
| ⇒ | If the DRLs do not illuminate, refer to Circuit/System Testing. |
| ⇒ | 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 Circuit Test. |
| ⇒ | If the test lamp illuminates, refer to DRL Circuit Test. |
DRL Relay Circuit Test
- Ignition OFF, disconnect the C4 harness connector at the BCM.
- Ignition ON, test for B+ between the control circuit terminal 23 and ground.
- Install a 3A fused jumper wire between the control circuit terminal 23 and ground. The daytime running lamps should illuminate.
- If all circuits nest normal, replace the BCM.
| ⇒ | 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. |
| ⇒ | 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. |
DRL Circuit Test
- Turn the ignition ON and the headlamps OFF.
- 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 supply voltage 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 supply voltage 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. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for BCM replacement, setup, and programming |
