Hi
we bought an A180 CDI for my wife despite the fact the engine management light was on, It was because she wanted a small car and because she is small she wanted an elevated driving position, parking sensors and heated seats were also a must. This car was fully loaded and was the only used car we found that fitted the bill, so we took a chance. I took it to the local Mercedes dealer as the vendor said his garage couldn't find any faults on the car. They said the DPF not regenerating was the problem. They found a leaking air pipe which they said was the cause but the DPF would still not regenerate because it was high mileage and too clogged up they said. Due to the age of the car they recommended DPF cleaning at a local company but the cleaning company said it was unlikely to be successful with 200k miles and suggested a buying a low mileage used DPF and having it cleaned. I decided against this as there were no guarantees of any value and the cost was £100 more than fitting the premium quality after market DPF from BM Catalysts which had a three year guarantee. With the new after market DPF fitted the engine light was finally off. Unfortunately it returned 8 miles later and the garage told me it was now showing throttle body. As no used or after market parts were available nationally we went for one of the five new throttle bodies still in stock with Mercedes Benz. The garage also put a deep clean product in the diesel tank as we suspect the problems have been around for a while and the previous owner kept clearing codes to get it through its MOT tests.
Once again the engine management light was extinguished for about 45 miles and then returned. At this point I have bought a code reader and the car now shows 14A600 positive control deviation of exhaust gas recirculation control is too high. If I clear the code it returns in a day or two. The EGR valve (part number A6401402060) appears to be only operated by vacuum so I don't know if any sensors are involved. Its only done about 100 miles since the cleaner was added to the fuel so I don't know if this could be the problem or whether it even does any good.
Replacing the EGR valve doesn't look difficult and its not too pricey £153 for the genuine part and £50 for after market. Can anyone offer any advice, should i go ahead and change the EGR valve or wait to see if the cleaning product does any good? The car runs perfectly no loss of power no smoke and a steady tickover. No starting problems either.

 

to give you an update I decided to take the car to a mechanic I trusted in Spain. he kept the car three days and found that (a) the EGR valve did not seat properly and he replaced it and (b) that an illegal EGR blanking plate had been fitted which would cause the 14A600 DTC every time the engine started. Mercedes work sheet says this is caused by an air leak, faulty EGR valve or carbonisation in the EGR circuit. Given that cleaning the MAF clears the problem it seems the issue is that it has more air than it expects because the MAF gives the wrong information. The previous owner did say that the problem started after a Mercedes recall, so I suspect that maybe he had the car chipped and the blanking plate was fitted then and coded out on the ECU.
Anyway it is no longer coded out.
The car was still throwing the code and he had it back for a day and afterwards said everything is working as it should and the long drive home may clear out some carbonisation.
It did improve things a little but then he rang from Spain and recommended cleaning the MAF sensor. After cleaning it the immediate difference was the acceleration, it would rev over 4000 rpm under load instead of 2200. it also didn't throw a DTC for a whole week then everything returned as before. I cleaned the MAfF sensor again and the DTCs disappeared and power returned, two days later faulty again so I have fitted a new MAF sensor..
Everything has been fine for 5 days but today the new MAF sensor has started behaving like the old one and the DTC faults have returned
I cleaned the air filter housing and fitted a new air cleaner before the new MAF sensor and I have checked for any evidence of oil mist in there but can find none.
Can anyone point me to what is causing the new MAF sensor to not function correctly after only 5 days?