My 03 envoy .when i switch to awd it will works for awail then goes back to 4x2

Hello, if the 4 wheel drive indicator stays on suggesting you are in four wheel drive, but you know it has disengaged, I'd be thinking more about an issue with the hubs not staying locked possibly? I don't believe that you would have a command given to disengage four wheel drive. As always, this kind of thing requires hands on inspection to find out what's going on, and analysis of the controls of the system.