I was adding some LED lighting to my 2023 F-150 XL Rattler 3.5L Ecoboost. I disconnected the battery negative cable and made the LED lighting battery positive connection (at the B+ clamp stud that has 2 connectrions on it and none of the LEDs are actually connected at this time). After reconnecting the battery negative, I am now getting a message on the instrumnent cluster screen saying the engine is in overtemp (the truck hasn't been run in over 2 weeks and shows before the ruck is even strted; it is cold) as soon as the key is put in accessory and there ia a P1299 DTC. If I start it, the truck runs very roughly (I think that is some kind of protection because the truck thinks it is overheating). Obviously I did something wrong. Can this be cleared w/o a dealer visit? BTW, where is this sensor located on the 3.5L Ecoboost?

 

Did you upset some cooling system wiring like to the front shutters when wiring the lights?
The 1299 cannot set until after the ignition is operated on because there is no power to the PCM until it's relay operates.
Revisit the places you did work at.
Good luck.

 

I did disconnect the left 2 of the 3 the large firewall header connectors (3"x4" connectors that have like 50 connections each) to remove the cover that is to the right of the engine bay fuse box. This covers the 3 or 4 B+ connections to the fuse box. I took it in to the dealer, luckily it is still covered, and they said that there was some corrosion on the pin for the temp. sensor that goes through one of those large header connectors. They cleanded the pins up and whala, all is good. I must have disturbed that corrosion when I removed the connector and then that corrosion was causing an issue after I plugged them back in.

 

Good to hear is worked out for you.

 

Depending on sensor design, a high resistance on the sensor signal will be seen as a high temperature so the high reported temperature would not be surprising with corrosion present like that.