Report: Transfer case control module
GMC Envoy Problem
Model Year Affected: 2002
Drive Train Affected: 4WD
Battery went dead in the Envoy one day. After replacing the battery the 4 wheel drive indicator light would not change with the selector and the 4 wheel drive light came on. After researching online I found that the engineers at GM forgot to set up the transfer control module with anything to save the memory, so basicly, it didn't know what to do. It also said you could take it to a dealer and they could reflash it for $100 and hope you never have battery problems again or locate a used one (2003 or newer because GM corrected their screw up after 2002 models). Make sure you research and get one that matches your 2002. Mine came from Ebay for $35 and was from a 2003 Trailblazer and it works great and I don't have to worry about the memory being gone if the battery goes.