My V40 diesel with 115k on the clock was running a bit rough last week and I thought it was probably the injectors needing a good clean out. I bought some Redex fuel system cleaner and put it in last weekend. I ran the car normally all week but it didn't seem to be clearing. So yesterday on my home from work on the dual carriageway I gave the engine a good hard run by revving it up to 4-4.5k revs in 2nd, 3rd and 4th before changing gear. I could see in my rear view mirror that I was leaving an enormous cloud of smoke trailing behind me and this did the trick as the engine is back to running smoothly. Ironically at this point the Engine Management System Malfunction warning light has come on. The manual says a fault has been detected in either the fuel or ignition system. This could mean that the engine does not meet exhaust regulations.

The car starts and runs ok and I cannot hear any unwanted noises from the engine bay so what could be the problem? Should I just persist with another dose of injector cleaner?

Finally, when I resolve the problem how do I stop the warning light coming back on or will it reset automatically?

not sure about the diesels, but on a gas model, you would get a code reader, read the codes, erase the codes, and get a beer :grin: the engine light might be lit because it probably did detect something off. you probably blew out all that crap with the your little rev-fest. the code is just telling you it knows what you did. just have them read and see what's up. it might amount to nothing more than a reset. keep us posted.

Thanks Greekmason - where do I get a code reader from?

Are you a biker also - looking at your avatar? I've got a BMW 1150GS.