Theory Of Operation

The Daytime Running Lamps (DRLs) illuminate when the Engine is running, the Park Brake is released and the Headlamp Switch is in the OFF or AUTO position. When the Body Control Module (BCM) receives a CAN message from the PCM, indicating the engine is running, a hard-wired input from the Headlamp Switch, indicating the Headlamp Switch is Off or in the AUTO position, and a hard-wired input from the Park Brake Switch, indicating that the Park Brake is released, the BCM provides a voltage output to the DRLs through the Right and Left DRL Lamp Driver circuits.