2004 envoy 4 wd quit working - 2004 GMC Envoy

I had TONS of issues with my 2001 Jimmy 4wd. A few things to check; the 4wd actuator switch, the vacuum switch, hub assembly, and the electronic 4wd dash switch.

Could be a bad dash switch but Envoy's and Chevy Trailblazers are notorious for bad 4wd actuators, which are located on the right side of the front differential. There is an electrical box that moves the shaft back and forth to engage the 4wd when you push the button inside. Look for a black box on the front axle with a wire going into it. Check that the plug is clean, apply a light coat of dielectric grease(available at most auto parts stores at the counter in a little packet) and plug it back in. If that doesn't work I would see a mechanic and get a professional dianoses.