Engine temp gauge not working

[bedrck46]

again still would be nice if you post the year etc of your expy

 

[joeuser123]

2005 ford expedition 5.4 Eddie Bauer

Sorry I didn't see you other post.

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[bedrck46]

its not a matter of seeing my post the more information you post the better answers you will get No need for everyone to be guessing

Temperature Gauge

The PCM receives the engine coolant temperature status through hardwired circuitry to the engine coolant temperature (ECT) sensor. The instrument cluster receives the engine coolant temperature data from the PCM through the communication network. The instrument cluster monitors the engine coolant temperature data received from the PCM and commands the temperature gauge indication with a corresponding movement of the pointer.


very complex circuit with many connectors and components

 

[joeuser123]

What can I test next, or is it just so deep in the electronics that I would have to take it to the stealership


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[bedrck46]

where in PA are you??

if you have the old CHT I would put the probe part in some water and take a resistance reading and then heat the water while you monitor the resistance There is a chart in the service manual that gives the different resistance reading at different temps. You could also get a variable resistor and connect it to the connector for the CHT and see if the gauge responds.

You need to start at Point A (CHT) and work towards Point Z (inst. Cluster) and check everything in-between. There is a good write up in the Ford service manual on the different things to check Its very lengthily.

Or take it to the dealership. But based on what you said about your mechanic I don't think I would go back to him

Right now it appears that you have been changing parts with the hope of curing the problem Getting a PCM off of e-bay is something I would question since you weren't 100 % sure your original PCM was bad

 

[joeuser123]

Thanks for the info. I will be purchasing a service manual. Is there page/section number you know of for the troubleshooting procedure? I only bought the PCM because I thought I had to take a road trip for work and with no ac it would suck. If the PCM was actually the problem(which is definitely not the issue) I would still have bought it used because I have 1200+ in this thing and I don't want to pay ford 1500 dollars for a computer that has less power than my iPhone. I live around the greens burg area


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[joeuser123]

UPDATE: My neighbor and me "fixed" the problem. We pulled the cover off of the back of the PCM connector to expose the wires. We jammed a 5k resistor in the cht sensor pins on the PCM connector. The gauge is now in the middle and the ac works. The expy runs great and now it has all of its power back. No check engine light at all.


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[bedrck46]

seems like you may have just put a band aid on it At least its working for the time being but with the 5K resistor you have a fixed input The CHT is more like a variable resistor That is part of why I suggested checking the CHT in water and heating it to see if the resistance changes.

Let me know when you get the DVD workshop manual and I'll get you the section numbers and page numbers to help you out Just send me a PM when your ready

 

[bedrck46]

If the CHT is good and the resistor helped you it would seem as if you have a open occurring in the circuit from the CHT to the PCM

 

[joeuser123]

Ok. PayPal has decided to stop working when I was about to order it. Thanks for all of the help. I will pm when I get the DVD manual. Glad I got it working temporarily, it's supposed to be 87 tomorrow


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