Hi - new to the forum and relatively new to MB (12 months) . I just wanted to share my experience of dealing with a P0470 and P0471 fault on my 2017 B Class W246 which has the 1.5 DCI engine (I believe its a Renault engine) incase it helps anyone solve their own issue.

About 3 months ago my engine light came on - it was slightly overdue a service anyway so thought it might be that, booked it in at a local garage, they did the service and said the fault was showing as a back pressure sensor, they said they call me with a quote but never heard from them again despite chasing. Anyway thought i might be able to fix it if its just a sensor, so did some research (including on here) and very things came up for P0470 which led to me changing the DPF Sensor. I bought a OBD2 reader, reset the fault and was very please with myself.

However as soon as i drove it came back on same error - stumped i decided to take it to an MB independent garage and (using Xentry) they said I'd changed the wrong sensor, the back pressure sensor was something different - so £95 for diagnostics and £290 to buy and change the sensor I drove out the garage annoyed I changed the wrong sensor but happy it was fixed. Then 2 miles down the road the engine light came back on, same P4070 error! I turned around and drove back - they said leave it a couple of days as it needs to bed in, sceptical i left - obviously it didn't and I went back and this time they said it was probably the MAF and we should change that.

The MAF looked fine on the OBD2 scanner, in idle it read 20 which was lower than the recommended range (30-300) but quickly went into the range on driving and looking about that seemed normal, so again I was sceptical. I spent hours looking into the the exhaust system and watching youtube videos on fixes, then i came across a similar video where someone had had a similar issue and had replaced all the sensors etc also. They then took it to a DPF specialist who took off the back pressure sensor and using a drill with bicycle brake wire attached to it, fed it down the pipe the sensor had come off which led to the exhaust to clear it out - and it fixed the issue.

So I set about doing the same - i first squirted a few drops of DPF cleaner down the pipe with a syringe and set about with my drill and cable, I was going at it for about 20 mins and it wasn't going in any further so was about to give up. Then I started the engine as i thought if it did link to the exhaust to monitor pressure then surely fumes would come out of it - but they didn't, so i kept going with the drill for about 15 more minutes and all of a sudden the cable went in further and fumes started to come out. I did it a bit long to make sure it was clear and put it all back together, reset the error and it hasn't come back since.

So if you have similar errors that come up, before going to the expense of replacing sensors just make sure the pipes that lead from them are clear. I was quite pleased with myself for fixing it but slightly annoyed at the Merc independent garage for not thinking or checking the pipes when they changed the sensor. I think this is the issue with alot of garages these days, they plug it into diagnostics and just change the parts it says on the computer without really thinking about it.

Hope this helps someone.