I was towing a couple of tons the other day and my car went in to the mode where it hangs on to gears longer. I plugged in my IID tool and it showed a transmission temperature of 140 degrees. When I dropped off the trailer and waited a while then drove home without anything on the back the temperature rose again up to close to 140.
This morning I drove 15 miles to work with no load on the car. At the start of the journey the temperature showed 34 degrees (ambient about 14), when I got here the IID tool showed 117 degrees, an IR temperature check on the sump showed 93 degrees.
As such it sounds like a dodgy sensor, but has anybody ever seen one fail like this? I would expect it either to work or not work. Any suggestions on the best course of action?

MC

I had the sensor fail on me. Drove 5 miles and got the "transmission overheat" message on dash. But later that day I drove
80 miles with no error message. Seemed worse if I was driving through traffic eg constant gear changes.

Anyway I had the sensor replaced (means new wiring harness for c£120 from land rover although I think you can find them for c£65) and new oil etc. all up it came to £500 but that fixed the problem.

Had a similar problems a couple of years ago on a drive back to Wiltshire from Cornwall, got 6 miles from home and got the trans overheat gearbox mode. We ended up replacing the radiator and trans oil cooler.

On the early 4.4's the bottom 6 rows of the radiator collapsed internally thus reducing the coolant flow to the trans oil cooler.

May just be a sensor but I'd get the radiator / trans oil cooler checked as well. There is a flow test that can be done on the radiator.

That was my first suspicion as well, particularly as sensors tend to either work or fail. When it reported 34 degrees when I started the car up this morning having sat on the road all night that looks like a sensor issue.

MC

I think the issue with the sensors is they rise but dont reset hence why it records a much higher reading than the actual temperature. Trick the system into thinking its actually overheating. Your IR reading would suggest sensor issues.