Transmission gauge dead, temp at 8,000 degrees

A couple of days ago I had my gauge go crazy on me and the dash started to light up and said to check transmission temperature and tow haul flashed. I left it alone, after I drove around a bit, the temperature according to Torque was in the 70's (obviously wrong) but the trans was functioning OK. Then the next day, all was well, no lights, not trouble, transmission gauge seem to register.



Yesterday when the Gage again went screwy, the truck started jumping in and out of gear and shifting incredibly hard. There was 10 second Period Where the truck completely disengaged even in drive. After the temperature went up on the gauge to about 70°, the truck started shifting normally again.


So after some research I figured it was the TFT sensor. I went ahead and replaced that sensor today. However now that I have everything back together I decided to do a quick check from the gauges to see if the sensor was registering properly now before I bolted the pan back up. My OBD scanner indicates that the sensor is still reading 8123.6° it does not seem to be changing. The dash gauge at key on shows the trans gauge being 'cold'. When you start the truck, the gauge goes completely dead, tow haul comes on, and truck complains about temperature of the trans. Torque app indicates temperature is steady at 8,000+ degrees.


EDIT TO ADD: Truck was not started without fluid. Only after I added fluid did I start the truck. Before I bolted the pan and filled, I tested the sensor with Engine Off/Key On to verify function, it did not read properly, so I bolted up and filled.




I visually inspected the connector in the transmission and the wires on it briefly and saw no issues. I filled up the transmission in hopes that it would work. Anyway it doesnt, so I suspect I'm going to be draining my brand new fluid. Before calling it a day, I checked wires under the dash, I traced the harness from the transmission to a box on the drivers side, All of that visually looks fine. No damage to the conduit. I wiggles all the wires I could reach around the transmission and where it terminates on teh firewall while I was hooked up to Torque, and the reading never changes.


Im at a complete loss and pretty bummed. This is my work truck, and I'm not sure how I'm going to get this fixed.

I attempted to test my old sensor with my multimeter. At about 68 degrees, the sensor reads about 30 kOhms. That number changes if I warm up the sensor. I now suspect that the old sensor was perfectly fine.


I need help desperately for troubleshooting this. I have never had any issues with this gauge for 166,000 miles. One day it was fine, the next it wasn't, and upon replacing the sensor with a new one, its even worse. At least before it would read SOMETHING that was in the 50-70F range.










Help please.....