Diagnostic Aids
WARNING: This page is about a different car, the 2001 GMC Safari and 2001 Chevrolet Astro. However, it is still accessible from the selected car via links, so may be relevant.
DTC U1000 does not normally identify a module failure. Check fuse supplying power to module with DTC. Check other modules capable of storing serial data DTCs (DTCs beginning with "U") before diagnosing serial data line. Check for DTC U1000 stored in other modules. If DTC is history, problem may be intermittent. Try to recreate fault by wiggling wiring and connectors while performing test.