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Discussion Starter · #1 · (Edited)
Evening. My 2015 Focus ST Diesel has got the engine management light on. I’ve read the code and it comes up with P2455 dpf differential pressure sensor high. I’ve changed the sensor which is fixed to the side of the battery holder and I’ve tested the electrical connector to make sure there is power going to the sensor. I deleted the codes and it was fine for a few journeys but now it’s come back on. Is there another sensor on the exhaust the other side of the dpf? What else could it be?
Any help gratefully received
Many thanks
Martin
 

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Have a look at this:
 

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2015 (65) ST-2 TDCi 185ps Estate in Deep Impact Blue
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Have a look at this:
Two months on after this repair, I can report that everything is still 100%, no more instances of EML / P2455 errors since. Definitely worth checking on your car.
 

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Discussion Starter · #4 ·
Two months on after this repair, I can report that everything is still 100%, no more instances of EML / P2455 errors since. Definitely worth checking on your car.
Thank you for the update. Even though I’ve checked that there is power to the plug, could there still be a broken wire?
 

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2015 (65) ST-2 TDCi 185ps Estate in Deep Impact Blue
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Thank you for the update. Even though I’ve checked that there is power to the plug, could there still be a broken wire?
Possibly, as you can see there's 3 wires to the DPF Sensor, I believe one is live, one is earth / negative, and the 3rd is the signal wire back to the PCM module, so it may be the signal wire that's broken.

Do you have a basic OBD Reader that just reads the OBD codes, or OBD cable and Forscan ?
In Forscan you can monitor the DP_DPF reading, if it's constantly high, say around 85 kpa then it's possible the signal wire is damaged so the PCM always see's a high reading, then puts the EML on. When running properly the DP_DPF reading should be fairly low, I think around 1-2 kpa at idle and rising as the revs build up.

The other possibilities are a blockage in the pipe from the DPF sensor, down to the DPF, some sections are metal, other bits are rubber, or probably worse case scenario the DPF itself is really clogged up.

Anyone have access to wiring diagrams to confirm which colour wire does what ?
 

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2015 (65) ST-2 TDCi 185ps Estate in Deep Impact Blue
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Just for reference, here's the original post that gave me the idea of checking the wiring loom on my car.

 

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Discussion Starter · #7 ·
Possibly, as you can see there's 3 wires to the DPF Sensor, I believe one is live, one is earth / negative, and the 3rd is the signal wire back to the PCM module, so it may be the signal wire that's broken.

Do you have a basic OBD Reader that just reads the OBD codes, or OBD cable and Forscan ?
In Forscan you can monitor the DP_DPF reading, if it's constantly high, say around 85 kpa then it's possible the signal wire is damaged so the PCM always see's a high reading, then puts the EML on. When running properly the DP_DPF reading should be fairly low, I think around 1-2 kpa at idle and rising as the revs build up.

The other possibilities are a blockage in the pipe from the DPF sensor, down to the DPF, some sections are metal, other bits are rubber, or probably worse case scenario the DPF itself is really clogged up.

Anyone have access to wiring diagrams to confirm which colour wire does what ?
That’s interesting.🤔. It’s just a basic obd reader. Maybe I need to invest in FORScan and use my daughters laptop to find out what it’s doing. Thank you very much for your help and knowledge. It’s starting to annoy me now but didn’t know where to look next.
 

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Discussion Starter · #8 ·
That’s interesting.🤔. It’s just a basic obd reader. Maybe I need to invest in FORScan and use my daughters laptop to find out what it’s doing. Thank you very much for your help and knowledge. It’s starting to annoy me now but didn’t know where to look next.
Was it an easy job removing the battery holder and air box to gain better access to the wiring?
 

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For me though surely before thinking it is an electrical issue or broken wire etc I would be looking at the dpf itself? If the fault code is saying there is too high a differential pressure could that be the issue before thinking it is an error in the signal? I would have the dpf out & check it & the various pipes to see if you have a blockage or mechanical issue meaning that the electronics are reporting the issue correctly which is what they are there for? Unless a sensor has failed - which can happen I suppose - a wire is unlikely to just 'break'. However a dpf can get clogged or blocked by the soot going through it? Especially if the car is driven on lots of short journeys and/or the dpf has not had a chance to get up to proper temps & do it's regen flushes fully?
 

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2015 (65) ST-2 TDCi 185ps Estate in Deep Impact Blue
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I had the fault last year took it in and it was a broken wire. still going good nearly a year on
Exactly the same issue with mine. It was your original post on this subject that lead me to checking the wiring on my car. The point at which mine broke was right on the joint where the DPF sensor wires join into the larger part of the loom. The wiring to the DPF sensor is pretty tight, so the regular movement and vibrations of the engine may be what caused the wire to break at this point.
 

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2015 (65) ST-2 TDCi 185ps Estate in Deep Impact Blue
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I’m thinking that’s what mine could be. How much did they charge you to fix it? Was it a main dealer?
Should your car turn out to have the same wiring issue as mine and @DavLinz2011 , it's not a difficult repair and easily achieved with basic toolkit of screwdriver, spanners and Socket Set.

It's possible to get at the DPF Sensor wiring without removing anything, but it's pretty tight to see and access with the battery tray and air feed pipe in the way, that's why I removed the AirBox, Feed Pipe, Battery and Battery Tray during my repair, just made it easier to get at the wiring loom.

Basic steps are as follows:

1. AirBox & Feed Pipe Removal - Disconnect the sensor near the AirBox, lift up the rubber flap where the AirBox Lid meets the Slam Panel, loosen the clamp at the top end of the feed pipe and pull that end free. The entire AirBox can then be removed as one whole unit, it just pulls upwards to release from it's rubber mountings underneath the AirBox.

2. Remove the plastic battery covers, Disconnect the battery terminals (Easier the remove connection to the rear negative terminal by removing the end that bolts onto the top of the suspension turret). Remove the metal battery clamp, lift the front of the battery tray upwards, it should release and fold down to allow the battery to be slid forwards and out of the battery tray.

3. Remove the DPF Sensor off the side of the battery tray.

4. Remove the battery tray, If I recall correctly there's 2 or 3 bolts in the bottom of the battery tray, once these are removed the whole battery tray can be lifted out, which then gives you much more room to access the wiring loom to check for breaks.

There's likely some videos on YouTube that also demonstrate how the remove these items, often the videos are are easier to follow than written instructions.

I'm certainly no car mechanic, I'm an IT Engineer by trade, but I found it to be a relatively easy repair.

If you're anywhere near the Northamptonshire area, I'll gladly help you check your car for the same potential wiring issue.

For me, this was a much easier option than removing the DPF and associated pipe work to check for soot build up and blockages, that would have been very much the last resort, or even a garage visit for my abilities.

Keep us posted on your progress, fingers crossed for a speedy and inexpensive resolution.
 

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2015 (65) ST-2 TDCi 185ps Estate in Deep Impact Blue
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For me though surely before thinking it is an electrical issue or broken wire etc I would be looking at the dpf itself? If the fault code is saying there is too high a differential pressure could that be the issue before thinking it is an error in the signal? I would have the dpf out & check it & the various pipes to see if you have a blockage or mechanical issue meaning that the electronics are reporting the issue correctly which is what they are there for? Unless a sensor has failed - which can happen I suppose - a wire is unlikely to just 'break'. However a dpf can get clogged or blocked by the soot going through it? Especially if the car is driven on lots of short journeys and/or the dpf has not had a chance to get up to proper temps & do it's regen flushes fully?
What led me to checking and finding the wiring break on mine was that I started with what I thought was easier fault finding for my abilities. Initially I was getting intermittent high DP_DPF readings in Forscan, so thought maybe the DPF Pressure Sensor was playing up. Brought a new one and replaced, issue then got worse to the point where my DP_DPF were permanently high and never budged. It was at the point my internet searches for suggestions led me to @DavLinz2011 post about the same issue with his car being a broken wire. For me that was something I was comfortable to have a go at myself, more so than getting under the car to start checking things in and around the DPF itself.
Totally agree, it could very well be a clogged up DPF or associated pipework, as you say it's probably more likely than the electrical sensor or wiring breaking, I guess it's a case of what @Martin82 is comfortable to have a go at himself.

I guess one of the keys to fault finding this is to check the DP_DPF readings whilst out on a drive, see what the readings are and decide from there what's the most likely cause.
 

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Discussion Starter · #15 ·
Should your car turn out to have the same wiring issue as mine and @DavLinz2011 , it's not a difficult repair and easily achieved with basic toolkit of screwdriver, spanners and Socket Set.

It's possible to get at the DPF Sensor wiring without removing anything, but it's pretty tight to see and access with the battery tray and air feed pipe in the way, that's why I removed the AirBox, Feed Pipe, Battery and Battery Tray during my repair, just made it easier to get at the wiring loom.

Basic steps are as follows:

1. AirBox & Feed Pipe Removal - Disconnect the sensor near the AirBox, lift up the rubber flap where the AirBox Lid meets the Slam Panel, loosen the clamp at the top end of the feed pipe and pull that end free. The entire AirBox can then be removed as one whole unit, it just pulls upwards to release from it's rubber mountings underneath the AirBox.

2. Remove the plastic battery covers, Disconnect the battery terminals (Easier the remove connection to the rear negative terminal by removing the end that bolts onto the top of the suspension turret). Remove the metal battery clamp, lift the front of the battery tray upwards, it should release and fold down to allow the battery to be slid forwards and out of the battery tray.

3. Remove the DPF Sensor off the side of the battery tray.

4. Remove the battery tray, If I recall correctly there's 2 or 3 bolts in the bottom of the battery tray, once these are removed the whole battery tray can be lifted out, which then gives you much more room to access the wiring loom to check for breaks.

There's likely some videos on YouTube that also demonstrate how the remove these items, often the videos are are easier to follow than written instructions.

I'm certainly no car mechanic, I'm an IT Engineer by trade, but I found it to be a relatively easy repair.

If you're anywhere near the Northamptonshire area, I'll gladly help you check your car for the same potential wiring issue.

For me, this was a much easier option than removing the DPF and associated pipe work to check for soot build up and blockages, that would have been very much the last resort, or even a garage visit for my abilities.

Keep us posted on your progress, fingers crossed for a speedy and inexpensive resolution.
Thank you for all that info that certainly helps and will have a look at doing this ASAP. Unfortunately I’m down in Kent but thank you for the offer of help. Your instructions are perfect and I’ll give it a go and see what I can find and let you know how it goes. Hopefully it is just a broken wire and nothing too expensive🤞. Thanks again for the info.👍
 

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What led me to checking and finding the wiring break on mine was that I started with what I thought was easier fault finding for my abilities. Initially I was getting intermittent high DP_DPF readings in Forscan, so thought maybe the DPF Pressure Sensor was playing up. Brought a new one and replaced, issue then got worse to the point where my DP_DPF were permanently high and never budged. It was at the point my internet searches for suggestions led me to @DavLinz2011 post about the same issue with his car being a broken wire. .........................................
I stand corrected then. If it appears that the design or installation leads to strain on the wire & it breaking then it could well be this. Which is why forums like this can be so good sometimes!! Some clever person at Ford probably thought it looked good & fitted well putting it all there & some penny pincher though they could save a few pence by making the wires that little bit shorter without probably asking the question of an actual engineer as to whether it would cause any issues! The end user is then left to pick up the pieces - literally!!
 

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2015 (65) ST-2 TDCi 185ps Estate in Deep Impact Blue
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After repairing the wire on mine, I stripped back more of the insulation so the wires for the DPF Sensor now separate from the main loom much further back, making the wire run to the sensor a lot more slack, still needs a bit of tidying up, but feel confident that it’s not going to break again.
 
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