Diagnostic Aids
WARNING: This page is about a different car, the 2000 Pontiac Firebird, 2000 Chevrolet Corvette, and 2000 Chevrolet Camaro. However, it is still accessible from the selected car via links, so may be relevant.
Check TAC module power and ground circuits and PCM/TAC module serial data circuits for intermittent connections. An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation.