Circuit/System Testing
WARNING: This page is about a different car, the 2008 GMC Sierra, 2008 GMC Cab & Chassis Sierra, 2008 Chevrolet Silverado, and 2008 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
- Ignition OFF, disconnect the harness connector X4 at the BCM.
- 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.
- 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 a short to voltage or an open/high resistance. If the circuit tests normal replace the underhood fuse block.
- If all circuits test normal, replace the BCM.