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Welcome, I'm Chris (aka Moose) I'm an independent contractor here at Just Answer.
I do have the wire diagram if its needed?
Does your scan tool have the ability to see what the PCM shows for coolant temp?
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Disconnect the engine coolant temperature sender and install a jumper wire between the Red/White wire and the Pink/Orange wire on the sending unit connection. This should result in the gauge pegging past Hot. Is that the result you get? if not then wiring is for sure the next step to check.
That test indicates the wiring and gauge are fine and you have ruled out the sensor. Are you sure it is not running to cold from a stuck open thermostat?
Based on the gauge moving, that is Fords test to indicate the gauge does work. The ECT does not actually measure temp. It will register normal coolant temp for a wide range of actual coolant temp. The upper radiator hose should be near 200 degrees at operating temp.
Does the cooling fan continue to run with the climate control off?
Anyway you can borrow a scan tool to get the CHT reading from the PCM?
I have never used a tool other than the Ford tools when working on a Ford. The NGS, WDS, and IDS.
If you can monitor both that would help.
The cooling fan which is controlled by the PCM indicates the PCM is showing running hot or its not getting a reading either and in a preventative measure state.
So that means the computer is getting an accurate reading from the ECT. The PCM uses the CHT reading for fan operation. With that ECT reading it can only mean the instrument cluster is to blame for the gauge issue.
There is a resistor inside the cluster on this circuit. It appears to be bad and not allowing the gauge to settle in the normal range even though the cluster is getting a correct reading. The PCM uses the CHT reading to know how to work the fan. Your CHT reading would have to be to high to result in continual fan operation. The cluster is replaced as a whole.
With what you have told me yes, 2 different issues.
you would need a scan tool that can access the CHT reading and monitor the cooling fan signal from the PCM.
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