2003 gmc envoy_slt_xl
I have had this vehicle for half a year. Winter is just ending and now we get a few muddy/slippery spots when parking or pulling out. When stuck I engage the 4WD - Hi and the light goes on and it seems to drive normally. However when stuck the rear wheels spin and the front ones don't move. Is it possible that the 4WD is not working even though it doesn't seem to give any error codes or warning signals?