Two problems related to automatic transmission control module have been reported for the 2003 GMC Envoy. The most recently reported issues are listed below.
While driving at 35-40 mph vehicle suddenly lost power and the steering was not operating . There was no response to the vehicle at all. This occurred in the middle of traffic of a major highway. Vehicle had to be towed to a dealership. A diagnostic test was done and the result showed the need to do an update of software for the transmission control module ( ecm) and the power train, in general. They performed the repairs. The vehicle was serviced the week before this occurred.
Vehicle was traveling a 65mph with no visible signs of trouble. The vehicle's pcm failed and the vehicle coasted to a stop and would not start. The pcm was replaced by the dealer and reprogrammed.