i have a 1998 audi a4 quattro with the 2.8 30 valve v6. i just got a 2.5 inch catback done and it came with an intake. also i used slick50 fuel system cleaner last week at the gas tanks i put 15-20 bucks in. the car seems to act fine, exhaust looks ok kinda white if i rev it hard, but it was cold. i dont notice any problems.

 

okay it's nice and all that this thread has been taken over for someone else's problem, but i'm still here hoping that someone can answer my question.

a diagnostic has been done when the light was on and no codes apparently were displayed - the auto place said it may have something to do with the fuel system (nice and vague, huh?!) and of course suggested we bring it back if happens again. It actually came on the other day again and without doing anything to the gas cap, it turned off the next day (it's probably gone on/off 20 times in the last few months).

 

do you have an intake? what was the weather like when it came on? im not trying to thread jack you, just figured why open a new one when theres already one about throwing codes.

 

P1198 and 1199 have to do with an electrical malfunction of both post cat oxygen sensors.. could be the heaters or the sensing element themselves..

 

post cat sensors? i had them fab me a 2.5in catback at lou's custom exhaust and there was no sensors after the cats nor bungs. but i was waiting for my friend to come check my CEL and it went off while i was waiting, i still had him scan it and only 2 codes showed up instead of 11, the two just being p1198 and p1199

 

was there sensors in the cats? my post cat o2's are actually like in the middle of my convertors.. and being a 98 i guarandamntee theres catalysts and monitors for them..

 

im so confoozled, he didnt touch the cats, only right before after the cats he made a short ypipe about 3 inches after the cats.

 

no intake - car is bone stock. the first time it came on, it was nighttime - probably 50 degrees and clear. now it will come on whenever - sometimes there may be a few weeks in between it coming on again (after we get it to turn off), other times it will pop on a few days later. sometimes opening the gas cap while the car is running, then turning car off, then on again will turn it off. other times that doesn't work, but what does it opening/closing gas cap before starting car after it has sat for a while (like first thing in the morning).

it's obviously frustrating as one hates driving a car with a warning light that you think is a fluke and then BAM! your car is dead!!!!

 

i agree completely, you cannot remove the gas cap at all oon the audis while the car is running and even if you do and you shut your car off, when you turn it back on its too late the code is already stored and even if you clear it, it may take a few cycles to work its way out fully. thats just what i was taught hoping im correct. what codes are you getting? btw dont pay 80 bucks to get your codes read.

 

no it is correct.. there is a fuel tank pressure sensor in most modern cars.. if the vehicle is running and there is a fluctuation in fuel tank pressure due to say.. a gas cap being removed.. then the sensor notices it and the ecu makes a log.. so do not run the car and fill up with fuel... but that doesnt necessarily mean that was the reason for the cel on .. you need to get codes pulled and relay them to us so we can try and help.. ;-)