04.5 6.0 f350 check engine/tow haul
 

Yesterday I pulled my steel gn 3 horse trailer about an hour each way. with the horses it weighs right at 7000 pounds. no issues. This morning I drove to town, no issues. This evening, I got in it to run down the road and about 2 miles from the house, the check engine light came on and the tow haul light started flashing and the temp gauge is dead. drives and shifts normal, tow haul button still functions. any suggestions before I take it to a shop? Truck is stock except for an EGR delete. No tuner, FICM was rebuilt. I had it on a battery minder before I left and was thinking about pulling the batteries and letting it sit for a while to see if it clears. Scan Gauge II shows no codes.

so I let it sit all night, batteries connected and it was completely normal this morning. will see what happens when I drive it to work tomorrow

So I just took it out for a test drive, went a couple miles down the road, shifting normal for a cold start. Temp gauge is working, just as I am almost back home. 5 miles at the most, temp is coming up to normal, gauge goes dead and check gauge light comes on and tow haul starts flashing. I think it might be the sensor. any suggestions on testing?

update:
So I stopped at my local diesel guy on the way home. He suggested cleaning the battery terminals and frame grounds to start. However, when I left his shop, the truck was already hot and it wouldn't shift out of 4th. luckily I only live a couple miles away. got home, went ahead and cleaned the terminals and both grounds on the frame. truck had cooled down by then. test drive went just the same, when it got up to temp, same as before, but it was shifting normal. stopped, shut it off, restarted and wouldn't shift into 4th again.

Update
 

Ended up being the TFT sensor. replaced and serviced the trans. no issues since.