Hi I have brought some dpf cleaner for my focus 1.5 tdci 17 plate mk3 have done now 66000 miles and service light comes on when I excelarate to over 3000 revs and sometimes comes on at low revs I only do very short journey's and about 3500 a year so I brought some dpf foam cleaner to try cos it may be full of soot and gunge I I thought try to flush it out can anyone tell me which sensor i take out on picture is it top or below so I can put it through it that's if it's the correct way to do it can you help thankyou...

I don't know this model so the specifics here may be completely wrong...
That looks like an Oxygen sensor which may be on the catalyst (catalyst usually before DPF and can be combined)?
I don't know where the DPF is but it will normally have two pipes (or one) coming from it to the pressure sensor.
Crucial that you find it and locate the pressure sensing pipe(s)
If you have the EML on, I don't understand why it goes off (unless you are simply switching it off?)

Does this model have a fifth injector (vaporiser plug - common issue, if it's not working, you'll never get a regen going)
BUT I know you state you only do short journeys and this could be a bit of a cause BUT BUT, I suggest you look at any fault codes and check the differential pressure across the DPF to see what it is and find out the reason why the filter is (or may be) clogged, how badly and why a regen isn't starting.
In my boring way I'll say DPF is usually a victim, not a cause so finding out exactly what is going on, checking there's nothing causing the pressure build up (if that's what it is) and sorting everything out THEN using your cleaner (should go in via DPF pressure sensor pipe in FRONT of the DPF)

I'll stop wittering on now and wait for someone else who knows these models better to say if anything I've said is correct by I think I would need more data to be sure?

Cheers for that yes I will also wait to see if others have mk3 diesel I'm no expert or mechanic I have just put a scanner on it because service light has come on again its saying P1102 I have just checked for air leaks but no sounds or leaks I have also cleaned maf sensors which are clean but soon ad I stop car and start up again the lights gone till next time may be days or weeks very strange to me...

Top sensor is lambda (O2) so don't touch that one.

Sensor with blue wire is pre-cat temp sensor so don't want DPF foam in there either really.

Best place is the rubber pipe which is on the right hand side, not shown on this picture.

 

On this engine, P1102 is often caused by a clogged EGR filter.

Thankyou that's very helpful to know 👍