In an 04 envoy do you need the transfer control module or will it cause problems

I would have to say yes. I'm not a mechanic but my 2002 Envoy lost the memory (smart GM engineers) after the battery went dead. My 4 wheel drive quit working and in the winter it was a trip. Do some research and get the GM # for your module (your 2004 doesn't have that problem with memory) and go on Ebay and buy a used one. I found one on Ebay from a 2003 Trailblazer for $35 that worked in mine. Its hard to get to. Mine was on the driver side dash nearest the door. It has and access panel on the end of the dash.Good luck.