Figuring out exactly what's wrong with it is usually a good place to start.
Ring 07885203889 I got one couple of weeks back
Try this link. I have a 2004 Envoy and mine is doing it. http://forums.trailvoy.com/showthread.php?t=48777
The under rear seat fuse box on a 2004 GMC Envoy XL is located beneath the rear passenger seat. To access it, you need to lift the seat cushion, which can usually be done by pulling up on the front edge. Once the cushion is lifted, you'll find the fuse box situated in the floor area, covered by a panel that can be removed for access to the fuses.
It is located under the second row seat
The 2004 GMC Yukon-XL has 61.3 in. of rear hip room.
The 2004 GMC Yukon-XL has 39.1 in. of rear leg room.
The 2004 GMC Yukon-XL has 65.1 in. of rear shoulder room.
The 2004 GMC Yukon-XL has 39 in. of rear head room.
The rear track of the 2004 GMC Yukon-XL is 5 ft. 6 in. (66 in.).
You can locate the transmission fluid in your 2004 GMC Envoy by using the transmission fluid dipstick. The transmission fluid will be in the transmission fluid pan.
The 2004 GMC Yukon-XL has rear wheel drive.
Its your relay switch... change it out and it should work..