Ground Circuits
WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
Check ECM/FICM connectors for corroded or loose connections. Repair as necessary. Disconnect ECM/FICM connectors. Using a DVOM, measure resistance between negative battery terminal and ground terminals at ECM/FICM harness connector. If resistance is more than 5 ohms, repair open in affected ground circuit. If resistance is 5 ohms or less, ground circuits are okay.