Over the past couple years I have been a quite member of this forum, but after reading no less then 500 post n the topic, spending over 10 hours trying to fix it myself, and spending over 1000 dollars at the shop I am in desperate need of help. (The truck is a 05 f250 with a 5.4l)

The problem first started out with the engine temperature gauge spiking and then resetting itself when the truck is turned off and then turned back on. If I drove the truck for any distance it would go into limp mode and the CEL would come on. The code was p1299, which is the cylinder head temperature sensor, and I replaced the sensor but no luck. Then the shop and I went through all accessories hooked up and couldn't find a short until I remembered that my prodigy break controller would occasionally read "ol" or "sh" which both readings are from shorts. I tow a enclosed trailer about 85% of the time and the past week I have been towing it with a different 250 and the same break controller without a problem so I have eliminated the trailer. But the shop just said the problem was the controller and unhooked it.

Now the next day it threw the same code with the controller unhooked and the trailer hooked up. after thinking it seemed that it was happening when i accelerated so I took apart the 7 pin and sure enough there was a little water in it, but after driving it around for a little and no code being thrown I hooked my break controller up and it still was showing ol or sh so i believe there is still a short. Also I noticed that my voltage is reading right at 13v instead of the 13.8-14v it was reading before this issue arose.

If anyone has had any experience with this I would be in your debt. I think I have narrowed it down to the 7 pin harness and/or electrical in the break components, but do not know what would loop back to the temperature sensor. Sorry this was so long but I wanted to give you guys all I know. Thanks for your time
-Ben

 

OK, let me see if I have this correct; You think that plugging in your trailer to your truck is somehow causing bad things to happen to your cylinder head temp sensor, which is causing the P1299 code?

Maybe

What is your voltage reading when your trailer is plugged in? Is it possible that the bad connection/water/corrosion at your 7-pin connector has caused your voltage to drop to a point where your cylinder head temp sensor is giving false readings?

 

As crazy as it sounds I think that the short causing the problem is the the trucks 7 pin harness. I have read a few places that people towing with a 7pin were getting this code. I dont know how it loops back to the temp sensor but I have not been able to find any other problem.

but the voltage does not change when I hook up or unhook.