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.

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 and the DRL 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

Ignition ON, observe the scan tool Ambient Light Sensor parameter voltage while carefully supplying sufficient light to simulate daylight conditions to the ambient light sensor. The voltage reading should be approximately 2-3.5 volts.

Circuit/System Testing

1. Ignition OFF, disconnect the X2 harness connector at the underhood fuse block.
2. Ignition ON, headlamps OFF, verify that a test lamp does not illuminate between the control circuit terminal E5 and ground.

^ If the test lamp illuminates, test the control circuit for a short to voltage.

3. Connect a test lamp between the control circuit terminal E5 and B+.
4. Observe the test lamp while commanding the daytime running lamps (DRL) on and off with a scan tool. The test lamp should turn on and off.

^ If the test lamp is always on, test the control circuit for a short to ground. If the circuit test normal, replace the BCM.

^ If the test lamp is always off, test the control circuit for a open/high resistance. If the circuit test normal, replace the BCM.

5. Ignition OFF, reconnect the X2 harness connector.
6. Remove the DRL fuse from the underhood fuse block.
7. Connect a test lamp between the relay controlled output circuit of the DRL relay and ground.
8. Observe the test lamp while commanding the daytime running lamps (DRL) on and off with a scan tool. The test lamp should turn on and off.

^ If the test lamp is always on or always off, test or replace the underhood fuse block.

9. 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

* Underhood Electrical Center or Junction Block Bracket Replacement.
* Ambient Light Sensor Replacement.