Circuit Description
WARNING: This page is about a different car, the 2005 Saturn L300. However, it is still accessible from the selected car via links, so may be relevant.
The daytime running lamps (DRL) relay is controlled by the body control module (BCM). Battery positive voltage is applied to the DRL relay coil. The BCM grounds the DRL relay control circuit in order to turn on the DRL relay. When the DRL relay control circuit becomes shorted to battery positive voltage, DTC B2603 is set.