Q: Reduced engine power on GMC Envoy 2003

The issue you are writing in about is common enough that a specific diagnostic, namely a Reduced Engine Power Warning Light Diagnostic is performed by technicians dispatched by YourMechanic. If you request that diagnostic, the responding certified mechanic will get this issue resolved for you. In your circumstance, the vehicle’s powertrain control module (PCM) has undoubtedly stored one or more diagnostic trouble codes that will identify the "general area" in which the fault lies in the engine management controls. Although the throttle control system is a common trouble area when the Reduced Engine Power Warning Light illuminates, there are quite a few other components and systems that could come into play and, of course, there is always the possibility of multiple, or "coincident", faults. Here are some of the possibilities that YourMechanic diaspatched technicians would consider:

Defective throttle position (TP) sensor
Defective oxygen sensor
Defective accelerator pedal position (APP) sensor
Loose or damaged wiring
Defective throttle body
Defective powertrain control module (PCM) (not typical; ONLY if a long, long list of other possibilities is ruled out)
Any fault/error that will affect drivability function
Any fault/error that will affect vehicle performance
A fault/error in the emissions system
A fault/error in the throttle control system
A fault/error in the transmission control system

The Reduced Engine Power Warning Light is considered serious because of the immediate and severe drivability problems that will be present until the engine or transmission fault is repaired. If you request the recommended diagnostic the mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.