Trans Temp reading ZERO, guage laying flat

Sounds like a broken wire.

 

Wiring , sensor
Yr tranny fluid flat out cold like your ex heart

 

After you've run the truck reach under and touch the main box. Should be warm (180°f). Most likely pavrom is right.

 

I’m curious if your trans temp gauge is on your display screen or as a separate gauge?

I have a 2014 t680 with a manual gearbox and my gauge never moves and is on my display screen..

 

Oh no, your transmission is freezing up,,,sending unit fried. It's not the most important gauge. In all my years, I never had a transmission "overheat".

 

I usually contact Caitlin Jenner and Chelsea Manning with all my tranny issues.

 

Several years ago I bought a truck with a 10 spd auto shift. I picked it up in Indiana and bobtailed it to New Mexoico. I had only gone about 30 miles and was already kicking myself for buying the thing, when I noticed the trans gauge was almost pegged. I stopped and felt of it, it wasn't hot, but it bothered me looking at that gauge enough, that I stopped and bought a point and shoot thermometer. lol

A few years later we were on a job in Neveda, and my driver told me on the radio that I had better come check it out, his tranny was hot, now he had been driving that truck over a year, and just noticed the gauge would be showing hot within 20 minutes every morning. lol

 

I have 2 easy tests you can do to find out what the problem might be.
Locate the TCM and identify pins for the transmission temp sensor. Using a multimeter measure resistance of those 2 pins.(ex: temp sensor resistance 900-2000 ohms at 20*c) the reason for the "at 20degrees celsuis is because resistance values go up with heat. Called dynamic resistance. Therefore at 40*c the specs might be between 2000 and 4000ohms. ***These are just examples of specs*** you need to find you transmission manufacturer specs. Do the same for the guage. By doing this you've just verified the integrity of the connections from the sensor to the TCM and the guage to the TCM and all you did was disconnect 2 connectors. If say the sensor is faulty or the wiring your measurements won't be within the specs. Go test the sensor directly on the transmission with the same resistance test. If it's within specs it's guaranteed to be the wiring.
By doing test like this you'll save yourself slot of time, money and a massive headache.