Super76

Hello all, my 2009 A8L W12 had a CEL this week. I don't have VCDS, so checked the code with OBDII and had P0175 (Rich). The car is running completely normal with no idling issues, loss of performance, hesitation, etc...just the CEL. Gas consumption seems to be normal (about 12 mpg city driving with A/C on). I reset the code, and about 100 miles later got P0172 (Lean). I've started with just a fuel system cleaner and tank of gas to see if that helps, and may also try cleaning the MAF. Without any issues in performance, is there a place anyone recommends I start looking, as I try to diagnose? I've tried to search the forums (I'm new to this), but everything I found for these codes was accompanied with some type of performance issue, which I'm not experiencing. Thanks in advance.

Giovanni Giovino 6.0+6.0TT

Hello Super76,
Welcome aboard, my 05 W12 recently had similar issues with lean/rich codes, after much checking of many items it came to be the fuel injector's O-rings, so instead of trying to pinpoint which cylinder was the cause I just swapped all the injectors and O-rings from a Bentley W12TT I tore down, yes the twin turbo injectors are a bit larger, but all is good, and I fell more power in the seat of my pants.

MP4.2+6.0

Welcome. Hard to know without more specifics. For codes like those, I would also expect them to be side of motor (head) specific, since all the relevant monitoring parts leading to codes like those are divided up by side--O2 sensors, throttles, MAF's, intake air feeds, etc. You likely need a better quality scan, like VCDS.

Yes could be injectors/seals. Could be a basic vacuum leak. Could be MAF. Could be a failing O2 sensor. Could be... need more diagnostic info. Net, hard to pin in down from the arm chair.

P.S.: W12's have two engine computers, not just one. Your typical throw away OBDII code reader can only reach the main one, at most finding a code to check the other one. VCDS or other pro/dealer equipment will reach both. You want to check and reset codes in both of them.

TSHong

+1, it's hard to diagnose with a basic obdII reader. Also you probably have multiple issues if you have had both rich and lean codes.

Super76

Thanks all! I've ordered a VCDS. Will follow up once I can get some better diagnostic info. Very much appreciate your help!