Cylinder Head temperature sensor issue

[OCJR]

Hey good people I’ve got 350k on my 2008 Expedition . I was riding along came to a stop and it started idling rough and shut down with a P1288 CHT(Cylinder Head Temperature) sensor out of Read
Codes range. I changed the sensor repaired some wiring and it wouldn’t start but the code changed to P1289 CHT(Cylinder Head Temperature) sensor high input. And the p1288 code is gone. I’ve checked the voltage from the PCm to the sensor and back to the PCM and it’s correct. Also checked the sensor’s resistance with a change in temperature and it’s also correct. The truck still won’t start and the code wont clear. Any suggestions on where to check next? I would greatly appreciate it. Thanks in advance.

 

[AWAR]

I have found small rodent evidence on many 4.6 and 5.4 Fords. Seems they like the insulation on the wiring. I would check the wiring all the way to the sensor. It is easy to access after you remove the alternator.

 

[OCJR]

I’ve done the wire repair from the sensor to the connector behind the intake manifold. But I’ll check further down the harness to see if there’s any other wiring issues. Thanks!

 

[Dustin Gebhardt]

Where are you testing the voltages?

With everything connected, I'd backprobe the wires at the PCM and check the voltage as close to the PCM as possible.

On my '07, the previous owner has sandwiched the wiring for the CHT sensor between the intake manifold and the head. 150k miles later, the insulation on the wiring gave out and caused all sorts of temperature related issues. Of course, this was during a cross-country family vacation. So, in the parking lot of Circus Circus in Las Vegas in late July, I pulled the intake manifold and installed a new CHT sensor and then the short wiring adapter from the sensor to the main harness.

 

[OCJR]

I checked the voltages at the PCM coming out and going in. And I also checked at the sensor going in and out also and the reading showed correct. Just not sure where to go from there.