The trans temp gauge in my 2002 Denali bounces up and down from 100 to normal. When I say bounce, I don’t mean changes in temperature, but fast enough to mean erratic connection. Should I start the sending unit or gauge?
Dont forget the connection behind the instrument cluster also. They sometimes get oxidized and cause a bad connection. A pencil eraser usually does the trick. Could be a bad solder joint on the cluster too.
Great point. The live data will rule out one side or the other. If the live data is bouncing around like the gauge is then indeed the sensor or its wiring harness to the PCM is the problem child. If the live data is steady as a rock then all of that part of it is fine and the problem is strictly in the Instrument cluster all the way back to the output of the PCM that feeds the tranny temp signal including that wiring harness part of it. Sounds like a blast!