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 daytime running lamps (DRL) are controlled by the body control module (BCM). The BCM grounds the DRL relay control circuit in order to energize the DRL relay coil. The DRL relay then sends voltage to the low beam headlamps.

Circuit/System Verification

1. 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, then covering to simulate darkness. The voltage reading should change from approximately 0.69 to 4.52 volts.

^ If the reading does not change between light and dark, refer to the Ambient Light Sensor Circuit Test.

2. Connect a test lamp between the relay side of the DRL fuse and ground.
3. Verify that the test lamp turns on and off while commanding the daytime running lamps ON and OFF with a scan tool.

^ If the test lamp does not turn on and off while changing between the commanded states, refer to the DRL Relay Control Circuit Test.

4. If 1 or both of the daytime running lamps do not turn on and off, refer to the Daytime Running Lamps Circuit Test.

Circuit/System Testing

Ambient Light Sensor Circuit Test

1. Ignition OFF, disconnect the harness connector at the ambient light sensor.
2. Ignition OFF, test for less than 1 ohm of resistance between the listed ground circuit terminal and ground.

* Ambient light sensor terminal B
* Ambient light/sunload sensor terminal C

^ 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 4.5 volts.

^ If less than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the BCM.

4. Install a 3A fused jumper wire between the listed signal circuit terminal and the low reference circuit terminal. Verify the scan tool light sensor parameter is less than 1.0 volt.

* Ambient light sensor terminal A to B
* Ambient light/sunload sensor terminal D to C

^ 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.

DRL Relay Control Circuit Test

1. Ignition OFF, disconnect the harness connector X4 at the BCM.
2. Ignition ON, verify the daytime running lamps are not on.

^ If the daytime running lamps are on, test the DRL relay control circuit for a short to ground. If the circuit tests normal replace the underhood fuse block.

3. Install a 10A fused jumper wire between the relay control circuit terminal 23 and ground. Verify the daytime running lamps are on. are on.

^ If the daytime running lamps are not on, test the DRL relay control circuit for an open/high resistance. If the circuit tests normal replace the underhood fuse block.

4. If all circuits test normal, replace the BCM.

Daytime Running Lamps Circuit Test

1. Ignition OFF, disconnect the harness connector at the affected headlamp.
2. Test for less than 1 ohm of resistance between the ground circuit terminal B and ground.

^ If greater than the specified range, test the ground circuit for an open/high resistance.

3. Connect a test lamp between the control circuit terminal A and the ground circuit terminal B.
4. Command the daytime running lamps on and off with a scan tool. The test lamp should turn on and off when changing between the commanded states.

^ If the test lamp is always on, test the control circuit 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 for a short to ground or an open/high resistance. If the circuit tests normal, replace the underhood fuse block.

5. If all circuits test normal, test or replace the affected headlamp.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

* Ambient Light Sensor Replacement
* Headlamp Bulb Replacement (GMC) Headlamp Bulb Replacement (Chevrolet)
* Underhood Electrical Center or Junction Block Replacement