Road Test
WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
If a visual/physical inspection does not locate the cause of the problem, drive the vehicle with a DMM connected to a suspected circuit or use a scan tool. An abnormal voltage or scan reading, when the problem occurs, indicates the problem may be in that circuit.