Ok I don't expect anyone to diagnose my car first off. But I am looking for opinions. 01 Turbo Quattro threw a check engine light at me after a fuel fillup. I assumed I was stupid and left the gas cap loose so I went to a friend at a valvoline oil change joint to clear the code and it ended up being a o2 sensor bank one sensor two code. I believe it was running rich, I didn't get a chance to see the code before he deleted it so quickly. It came back on today so I will find out again what it was. I dont always say hey bad o2 sensor because its not always that. The MPG thingy on the heads up display (sorry im a first person shooter video game nerd) is going haywire now too. one second Im getting 100mpg the next second Im getting 7. and I literally mean within a second it changes. and to every number in between. I have a feeling thats playing a role in it. Can anyone tell me if they have seen this before and can give me some insight. I'd appriciate it.

 

ok I went to advanced auto again and re-ran the codes. if anyone could give me some insight on this craziness.

P0136- Post catalytic o2 sensor circuit malfunction
P0442 - Evap system small leak.

has a gas leak I've noticed now too on the left side rear. so Im thinking the second one may be a leak at the evap can. or the LDP. but yeah I don't think those take in the much gas and this seems like a bigger leak then just a "small" as the odbII implies. plus the o2 sensor and the evap can really don't have anything to do with one another. But audi's seem to be such a weird beast that I could never be really sure.

 

the rear o2 sensor should have not affect fuel consumption at all. it is only used to monitor how well the catalytic converter is functioning.

given that it says circuit malfunction, you should check the wiring and test the sensor before you bother replacing it. but like i said, dont expect a new one to change your gas mileage.

 

I already assumed that. I knew the post catalytic one doesn't send any message to the ecm about fuel consumption. and a circuit malfunction doens't mean a bad converter. so wiring makes sense. just a circuit tester then is your advice?

pretty sure the fuel consumption has to do with the fuel leak that I have that keeps appearing and disappearing. not sure how one minute I have a fuel leak and the next I don't but now its throwing a evap code and its confusing me. if you have a idea about that i'd appreciate it.