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Just wondering does anybody know what the electrical connectors on top of the fuel filter for a Mondeo Mk4 1.6 TDCI are for?

I can see there are 2 electrical sockets on the fuel filter.

The wiring loom on my Mondeo only seems to have a plug for one of these sockets.

When I had a look yesterday trying to diagnose an injector pressure issue, I noticed that this plug was not plugged into the fuel filter (see photo).

So, just wondering what it's for because the car was driving for at least 2 years this way.






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One will be for the Water in Diesel sensor, the other will be for an in filter Diesel Heater that cars in our climate do not come equipped with even though the filters come with the electrical socket 

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Ah OK. So it must be the Water in Diesel sensor that was disconnected. Thanks for the info.

Does anyone know if having that disconnected could cause a problem?

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I wouldn't have thought so unless the diesel did have water in it. If it did then it would show when you plugged it back in. 

If the filter has been there for two years then it would be a good idea to change it if you are having fuelling problems.

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I think that one is actually the fuel heater.  The central one is a drain plug that goes right through the middle, it twists and lifts up to drain water from the bottom if necessary.  I never have been sure why it's plug shaped - it may incorporate a water sensor if there are pins in there.

The water in fuel sensor has to be low down.  Water conducts electricity but diesel doesn't, and it's specific gravity means that the water will settle at the bottom of the filter.  When it reaches the level of the sensor, it will complete the electrical circuit and illuminate the dash warning.

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Here's a photo of the new fuel filter:



You can see there are two electrical connectors, but only one is connected to the wiring harness.

This one is connected:



And this one is not:



So, do you think the one connected is the fuel heater?





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Yes the connected one is the fuel heater.  It's there to reduce emissions rather than being a necessity in our climate.

As there's a single pin on the central plug, it looks like that does incorporate the WIF sensor - but I've not seen one connected on either the Focus or Mondeo.  Maybe there's no dash warning on the later cars.  

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