Listen, let me tell you my DPF experience. I have a Vito van with the 3.0 turbo diesel engine and it goes great, I use it for transporting my bikes and ONLY for long trips. When I drove over to the UK recently the van started to go into limp mode in France, very frustrating cos it would take about 5 mins to get up to 135kph on the motorway whereas it usually accelerates fairly fast for a van, and on any uphill stretches the speed would then fall right off to a 100kph crawl.
In the UK I asked some mates what they thought and they all said a clogged DPF. Just at that moment 2 friendly AA guys came into the motorbike shop for a coffee, they offered to help and they went thro the standard procedure to resolve the DPF problem, running her at 3000rpm for 2 mins etc etc, all was good but I found it very strange that I had just covered 2000km at 3000 revs!!!!
Long story short, when I got back to my friendly INDI guy in Roma he put the van up onto his ramp and we inspected the DPF which was almost as clean as a whistle!!!!! So he ordered one new sensor and indeed after two trial runs we discovered that one of the two DPF sensors was defective and was telling the ECU that there was a fault, which then sends the engine into limp mode. These sensors measure gas flow and if there is a large difference between the before and the after sensor then this signals a blocked filter.
The van has now covered another 15k kms without any reproduction of this error. Of course these sensors and connectors are underneath the van so exposed to muck, heat, vibration, water and all the rest so I guess that after 9 years (the van is a 2009 model) this kind of error is not a big suprise. The sensor cost 30 Euro ish thro Mercedes. Needless to say while I had the opportunity I sprayed the underside of the van with WD40, just to try and help her resist rust and ageing and stuff.
Thanks for the advice and sorry it's about an a1 and not a5 ?. I took it out tonight whilst watching the info and it was quite interesting watching the dpf temperature in relation to revs and load. The dpf regenerated whilst driving as you can see in the screenshots. I still have the negative reading but as its regenerating I guess it's ok.