Conditions for Setting the DTC

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2003 GMC Yukon XL, 2003 GMC Yukon, 2003 Chevrolet Tahoe, 2003 Chevrolet Suburban, and 2003 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.

When the park lamp relay control circuit is open or shorted to ground.
When the BCM receives a park lamp ON command and the park lamp relay control circuit is shorted to voltage.
When the park lamp relay coil side is open or the battery positive voltage to the low beam relay is open.