I purchase a Mk4 2.0l Diesel from a friend at the end of August last, he had the car from new and serviced it regularly at a main dealer; as I have done so.

The first day I drove to work in it the Engine Management light came on, I got the RAC out and he said the PDF was blocked.  Not knowing the sort of journey the had on a daily basis before I had it I thought my drive to work and back (40 Miles one way all Motorway) would clear it; it did not.  I took it to the main dealer who said it was the sensor which they were going to charge me an arm and a leg to change.  Once I found out where it was I got a genuine part and done it myself. 

After I finished not only wad the Engine Management light was one the Engine Malfunction light was on too; that was because the pipes from the sensor to the PDF had crumbled and need to be replaced too; the main dealer done that but all the light were still on.  The next thing to be changed by them was the PDF Filter; the light were still on, the dealer is now telling me the Power Train Management Unit (PTMU) is at fault and is corroded and which is two arms and two legs to replace. 

After thinking about it I thought the problems really started when I put the new sensor on and as I still have it I will put that back on; that when I discovered the fitter had not put the plug in the sensor so I went back to the dealer who plugged it in and the lights went out apart from the engine management light.  I was happy with that and I know the car would pull again when accelerating; which it did at first but again the Engine Malfunction Light come back on... AHHHGGGGGG!

Anyone have an idea?

I have written to the CEO of Ford saying what a great place the designers put the PTMU, in the wheel arch behind the fog lamp in the driest place possible where water and damp cannot get to it... NOT!    

1 hour ago, Agusta said:

After thinking about it I thought the problems really started when I put the new sensor on and as I still have it I will put that back on; that when I discovered the fitter had not put the plug in the sensor so I went back to the dealer who plugged it in and the lights went out apart from the engine management light.  I was happy with that and I know the car would pull again when accelerating; which it did at first but again the Engine Malfunction Light come back on... AHHHGGGGGG!

Just to get the simple thing out of the way first, there is no chance that you have swapped the two pipes to the sensor (at either end) is there?
 

Thank you for your reply, no, the pipes are different sizes and the technician at the dealer put the pipes on so I would hope he go that right. 

They put the pipes on at the main dealer and didn't notice the plug hanging loose!?

The Focus PCM is also in the same place but it's so well sealed there's no chance of water getting in there.  Have you got any specific fault codes or anything to go by?  If it was the PCM corroded you'd usually get several engine sensor faults at once.

I done a test and there are two DTC codes, 160782 & C40168. 

They're from the cluster test I think?  They're not 'normal' codes so I don't know what they are I'm afraid.  The C probably relates to chassis though, and neither start with P which would be for the PCM.

If you can get some proper DTCs from a code reader that could be more helpful.

In full tradition like the car my code reader has decided to pack up.... I hate cars.  I will try and get the codes some how.