Hi, any help would be great my duramax temp gauge works like it should when started for the first time in the day but when I try to leave work for lunch after about 5 hours of it sitting the gauge will peg at 300 or stay at zero no mater how much I drive but if I let it run for awhile when it’s at 300 it will drop to zero and stay there. I’ve used i temp gun to see what the tranny pan was at while the gauge says 300 and its cold I’ve replaced the internal wiring harness and the transmission temp sensor, new fluid and filters. But during the winter time the gauge reads perfect. My guess would be a stepper motor or wiring problem but it doesn’t add up why it would work fine in the cold. I can tell the TCM was replaced from whoever had it before me. I will get codes everyonce in awhile but they go aways after driving for alittle while. The codes I get are P0700 transmission control system (MIL request) p0711Transmission Fluid Temperature
Sensor ACircuit Range/Pertormance and P0712 Transmission FluidTemperature Sensor A Circuit Low Input. Thank you in advance for your help