2012 Navigator Cylinder Head Temperature Sensor

[Chackett]

All-

I feel like this is a long-shot, but going to give it a go anyway.

I have a 2012 Lincoln Navigator with the Ford 5.4l 3v engine. I had let a friend borrow it for a while, and now that I have it back there are some issues. Dead battery, AC Compressor Clutch not working, temp gague in instrument cluster not working, the temperature icon is illuminated on the dash. There were various codes, but most interesting was P1289 - Cylinder Head Temperature Sensor "A" Circuit High.

As usual, I just threw some parts at it and replaced the battery, the thermostat, and the cylinder head temp sensor. Problem persists

When I clear the code via ForScan, the temp gauge will briefly spring to life and appears to accurately show a normal / expected temperature, but within 3-5 seconds, it will throw the code again, the temp gauge dies, and the auxaillary fans kick on (as if it believes the engine is hotter than it is).

Any ideas? I'm doubtful that my new cylinder head temp sensor is bad. The fact that when I clear the code, the gauge briefly comes to life, makes me feel like the actual gauge is functioning properly. Am I hunting down a short now? Ugg..

I really don't want to have to pull the intake to get at that cylinder head temp sensor. I was able to use a 19mm flex head gear wrench to swap the sensor without removing the intake. Thoughts?

Chris

 

[joegr]

I would expect that a "high" code would mean an open instead of a short, but I suppose it could be inverted. I'd trace the wiring from the sensor to the PCM and verify that it has continuity all the way and that it is not shorted to ground. What is the voltage on that signal with the sensor connected and with it not connected?

Note that head temperature sensors are usually one time use, so don't remove the new one unless you are going to replace it again.

 

[Chackett]

Thanks. I'm going to start tracing wires and looking around for evidence of a rodent or other funny business. Seems too coincidental that the cylinder head temp sensor AND the AC clutch start misbehaving at exactly the same time. Generally speaking, I don't believe in coincidences.

Very interesting about the sensor being a one-time use thing. It seems like any other kind of sensor that threads into its receptacle. Does it have to do with the heat / expansions / contraction that happens in that location?

Thanks!
Chris

 

[joegr]

Your sensor may be different, but on the ones I have seen, the end of them crushes into the head to make very good contact. If you remove it after that, then the tip is distorted and may not make good enough thermal contact when you re-install it.

Also note that a faulty head temperature signal is likely to cause the PCM to disable the AC because it thinks the engine may be overheating and the last thing it needs is more heat caused by the AC system.

 

[Chackett]

Well .. I definitely found a wire that needs some attention. This connector comes from under the driver side of intake. It really couldn't be much harder to get at, and while it is definitely A problem, I don't know if it's THE problem. I'll guess I'll start trying to figure out how to repair this and we'll go from there..

 

[Chackett]

OK. I decided to quit screwing around and I removed the intake manifold. Sure enough there is definite rodent damage. 2 questions.

1. Can anyone tell me what this is? Can I repair it by wrapping / sealing it up or does it need to be replaced? I don't even know what it is. There are 2 pics....one to show the general location of it, and the other a close up:

2. I have never had to make repairs to a wiring harness like this. How can I locate some diagrams that might help me figure out what this is and make sure I re-connect / wire it correctly. One of these is chewed so close to the actual connector, I would think maybe I need to replace the whole connector? What a frickin hassle.

And here is a close up:

Here are a few photos of the wiring harness that was chewed. It's tough to see, but there are at least 3 places where it's chewed and I'm really looking for some help making sure I get it re-wired correctly:

 

[04_Sport_LS]

Best option would be to go to a "pick and pull" (diy) junkyard... and get as much of the needed harness as you can.

Then solder up the wires, and use heat shrink tubing... If needed.