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Old 10-27-2012, 10:04 PM   #2
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Originally Posted by Ford Foci View Post
I have previously had the power control module replaced (april this year) to correct an overheating problem.

This part worries me.
I don't see any reason that the ECU/PCM should be replaced to fix an overheating situation.
It is true that the ECU controls the cooling fans, but not directly. The ECU actually sends a signal to a relay based on engine temp received from a coolant temp sensor.
I have never heard of a ECU not sending or receiving signals from good sensors.
So it just sounds fishy to me. But I haven't seen every possible scenario.

But the troubling part is how the ECU also controls the gauge cluster.
Signals the cluster display are first sent to the ECU from corresponding sensors/senders (coolant temp, crank position, vehicle speed, fuel level). In our US cars all these are sent down the same wires, but for your EU Focus they are sent down separate wires.
So we know the signals are all separate. Odds are 2 signal wires aren't going to fail at the same time. That leaves grounds and the question of do any share a ground. The answer is Yes.

I'm going off a wire diagram for a Mercury Cougar, which has the same wiring to the gauge cluster as your car. According to it, the fuel gauge and coolant temp gauge share a ground. This isn't at the connector behind the gauge cluster though; and I can't nail down exactly where the connector is. All I can find is the number of wires in it and that it may be green, should be 14 wires (or spots for wires).

I'm thinking this will be under the steering column somewhere.
I know it's in the vehicle cabin and not under the hood.

Find that connector and check the pins. Odds are one will be loose or disconnected.
If all's well then you have to follow the wires further.
There are no other connectors, which is what the electrical connector is called. But there are splices, 1 before and 1 after the connector. A splice is a group of wires soldered together.
You'll have to trace for these by hand and look again for loose wires.

If that doesn't solve the problem, the last part is the ground (or earth I believe you call them) at the battery.
There should be no other portion of a ground that would cause issue.

One thing to note is that a false ground might be able to feed backwards up the wire and cause a false reading to the ECU. So it could be the ECU was wrongly replaced, or replaced before a full diagnosis was done.

Best of luck and if you need any more help don't hesitate to ask.
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