The body control module (BCM) receives a signal from the ambient light sensor indicating a low or high ambient outside light level. Under daylight conditions the BCM grounds the DRL relay control circuit energizing the DRL relay. The now closed relay supplies voltage to the DRLs. Any time the headlamps are illuminated the DRL will not illuminate.

Schematic Reference

Headlights/Daytime Running Lights (DRL) Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Exterior Lighting Systems Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

Supply sufficient light to simulate daylight conditions to the ambient light sensor. Ignition ON, engine running, and the gear selector in drive. The DRLs should illuminate.

DRL Malfunction - with RPO TSH/TVC/TVD

1. Supply sufficient light to simulate daylight conditions to the ambient light sensor.
2. Ignition ON, headlamp switch in the AUTO position.
3. Observe the headlamps. The headlamps should not be illuminated.

⇒	If the headlamps are illuminated, replace the ambient light sensor.

4. Ignition OFF, disconnect the appropriate DRL relay.
5. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.

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

6. Verify that a test lamp illuminates between the B+ circuit terminal 86 and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the DRL relay.

7. Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.

8. Connect a test lamp between the B+ circuit terminal 86 and the control circuit terminal 85.
9. Command the DRL 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 ground. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

10. Connect a 10A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87.
11. Disconnect the harness connector at one of the DRLs.
12. Verify that a test lamp illuminates between the DRL control circuit listed below and ground:

•	RPO W49/Z88 terminal 1

•	RPO WDA terminal 2

⇒	If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance.

13. Verify that a test lamp illuminates between the DRL ground circuit listed below and B+:

•	RPO WDA terminal 1

•	RPO W49/Z88 terminal 3

⇒	If the test lamp does not illuminate, test the ground circuit for a open/high resistance.

14. If all circuits test normal, test or replace the DRL relay.

DRL Malfunction - without RPO TSH/TVC/TVD

1. Supply sufficient light to simulate daylight conditions to the ambient light sensor.
2. Ignition ON, headlamp switch in the AUTO position.
3. Observe the park lamps. The park lamps should not be illuminated.

⇒	If the park lamps are illuminated, replace the ambient light sensor.

4. Ignition OFF, disconnect the DRL relay.
5. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.

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

6. Verify that a test lamp illuminates between the B+ circuit terminal 86 and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the DRL relay.

7. Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.

8. Connect a test lamp between the B+ circuit terminal 86 and the control circuit terminal 85.
9. Command the DRL 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 ground. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

10. Connect a 10A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87.
11. Disconnect the harness connector at one of the low beam headlamps.
12. Verify that a test lamp illuminates between the DRL control circuit listed below and ground:

•	RPO WDA terminal B

•	RPO Z88 terminal A

⇒	If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance.

13. Verify that a test lamp illuminates between the DRL ground circuit listed below and B+:

•	RPO WDA terminal A

•	RPO Z88 terminal B

⇒	If the test lamp does not illuminate, test the ground circuit for a open/high resistance.

14. If all circuits test normal, test or replace the DRL relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.