I've had the same issue and have spent thousands trying to figure out this is what it boils down to try this in the following order to save bunch of money ...
1) Pop your hood and disconnect the battery terminals let the car reset itself
2) Buy some di-electric contact cleaner, unplug your pcm wires and that big harness behind the fuse box, apply the di-electric cleaner and let it dry.
3) If that doesn't work, check the wiring harness that enters your transmission right next to the bell housing, those wires tend to melt and get exposed try splicing them and re taping them here's what mine looked like
- Now if that doesn't work then your going to have to replace your temp sensor that located in the valve body ... here is what it looks like
I have on extra just in case if you need it. It's $250 at the stealer and I'll give it to you 50% off.
Anyways moving, that's all the advise I can give you for now.
One other thing you might want to check is your water pump, what's your cars mileage?
Have you changed the serpentine belt, water pump ???
Let us know how it goes