Hi guys, I was hijacking someone else's thread and the replies I was getting weren't making sense so I thought I might as well start a thread and ask once in for all. I recently purchased a stock A3 with absolutely No mods at all and everything is absolutely fine with the car. I took it to one of these free health checks. They said everything is fine but the OBD came up with error Code P0171. The guys there said it best to change this sensor, which I now believe is the O2 Lambda sensor. The car runs absolutely fine, there is nothing unusual. Although I wastold that the mpg might be affected because of this. I managed 225 miles in half tank around London, which I think is pretty good. My question is if there is no engine management light and the OBD came up with that error, how would I know it is an error for sure? I wouldn't have known about the error if the guy had ran the OBD and would have been driving normally. I think the light does come on when I switch on ignition and then goes off, like other lights do when you switch on ignition, so in other words its not been disconnected or anything. Moving on, if it is an error indeed and I wanted to get it changed, is this what I will need? I was told it is an O2 Lambda sensor and this is what I can match. Also, how would I know about this error in the future? I mean I don't have an OBD and I can't just pop into garages every now and then just for fun to get my car OBD'd!! Where can I locate the MAF to clean that thing? I can't find any videos for A3 Thanks for all the help.