1996 Chevy Tahoe V8 Four Wheel Drive Automatic 170000 miles
i recently replaced the transmission and rear end in my truck and it was running fine and one day going down the road it would'nt down shift or shift into over drive so I replaced the speed sensor and it fixed it and I put a scanner on it too see if there were any more problems and it started doing the same thing and it is showing alot of trans codes and mass air flow sensors and cam shaft sensors but the engine is running too strong for that too be the problem a local mechanic told me that it sounded like an electrical problem but if I undo my battery cables breifly an re attach them it will run fine until I shut the engine off and it starts back not shifting right and not going into overdrive I only have 2nd and 3rd gear working
This seems to be a very common problem with this SUV.I have the same year and make as you and I have replaced the ECM(Engine Control Module) as refferred by a mechanic after testing my Trans. And was told all the modules shifted correctly on his test. Problem didn't go away. Replaced the Speedo Cluster. Problems didn't go away.
After researching for a few weeks now it's seems that this is a common problem and I cannot find anyone to answer how to make the problem go away. My feelings is that it's electrical somewhere.I have printed the entire wiring diagram and tested all the wires to and from each module and sensors back to thier respective head or computer. All have continuity, and test fine. Loosened and cleaned all body & engine grounds and retightened. One thing I have noticed while it is extreamely wet outside. Everything will work correctly for a minute or so. Gauges and even shifts through all the gears nice and smooth but soon goes back to 3rd gear after getting up to speed. That's what led me to think that maybe it was a bad ground.
Someone has told me that maybe the BCM(Body Control Module) May be bad?
I cannot afford to waste any more money on things that MAY be the problem. Someone has to know the cause or fix of this problem. Please Help us. Lol! Any and All help will be greatly appreciated!