nicholec7785

Ok, so I am new to the forum and don't know too much about cars but I'm eager to learn! I think Audis are solid cars but the parts/labor are expensive so I want to make sure I know what I'm doing. Last year my check engine light has been going on (P0430-catalyst efficiency below threshold (bank 2)). The car has always been a little touchy (jerking forward with little pressure on the gas) and when I took it to my old mechanic (great place) I got new spark plugs and everything was fine for a while. Recently, the light has been going on again and it seemed to be after I got gas so I started putting 89 in it (I know...I should have been doing this before). This seemed to help until this past month when the light went on twice after getting gas. By the way, I make sure it clicks so I don't think it is from a loose cap.

I've been researching this quite a bit and it seems like it could be a couple of things:
1. The O2 sensor is sensitive and I could do a reflash (if it applies to my make/model), have it tested, or have it replaced
2. The catalytic converter does need to be replaced, which I've heard is difficult with aftermarket parts because of tolerance?
3. An exhaust leak. Again I don't know much about cars and how to check this but I am definitely a do-it-yourself person.
4. Something I am unaware of

I do notice that the car now has trouble with power and has trouble getting going; sometimes I feel like I'm slamming on the gas to move (I previously drove a 1996 A6, that is still going strong, and it is starting to feel like that car but less steering control). There is also a weird oil-type smell (not gas) under the passenger seat but usually after it rains...I've also been told by my mechanic to try decarbonization which would be more beneficial than a fuel injection service.

Sorry this is so long. I just want to make sure I take good care of the car because I think it will last me a long time like the last one but I don't want to jump to any conclusions and go broke. So has anyone else had this/these problems? Should I be concerned and what should I check first? Also, if there are any good/honest mechanics in the Northern VA area that anyone would suggest I would really appreciate it!

Thanks!

rpmk42

I wish I could be of some help with those problems, but unfortunately, I have no answers for you. However, as a fellow do-it-yourselfer, I applaud your effort. I have a '99 A6, and although in my opinion it's been a great car, it's still needed some occasional non-routine maintenance. For things such as that, I often go to the following site:

www.audipages.com

It's for an A8, but you'd be surprised what's applicable to the A6 C5 platform. It's been very helpful to me while I've owned this car. Also the technical articles under the Resources heading above (on this website) have been very helpful as well. Other than that, just keep searching here and hoping for a response from someone who knows.

Anyway, good luck with these issues. Sorry I couldn't be more help

rs4-380

actually sounds alot like exactly what the OBDII code indicates, a plugged catalytic converter. This would cause reduced power and hesitation. The fuel smell could be a result of the problem, or actually a cause of the problem. If the engine is dumping raw fuel into the exhaust you would need to figure out why it is doing it before taking care of the cat

jschick

this could be many things. and hard to diagnose without seeing the car.
But first the basics. the Audi is sensitive to vac leaks, do a search on the vac pump, it looks like a little black plastic Y about 4 inches long, just to the right of the throttle body under the plastic cover. this gets clogged and needs to be cleaned with normal maintenance, as for running badly after filling with gas, this could be a vac leak or a purge valve sticking. you can search on this also, but in the emissions system their is a valve that directs fuel vapors into the charcoal canister, if this valve sticks open it will put vapors in the engine causing hard starting after fill up.
as for the converter, best way I know to test his is to run the car hard for a few minutes after dark, and then look under the car at the cats. if one is glowing red then it is Bad.
the vac leaks will cause check engine lights to come on and bad idle oil leaks etc, but really shouldn't cause major drive ability issues.
you could also have a bad or dirty throttle body or a bad O2 sensor.
best bet is to find some one with Vag-com to scan the car and get better codes then generic OBDII. you would be much better buying a cheap ebay interface and downloading the free version of Vag-Com then getting generic codes. but if you really want to start some DIY on your Audi Buying the vag-Com will be the best money you spend! it's about $250 then you can do about everything the dealer can do with help from this forum

nicholec7785

Wow I really appreciate all of the advice!

rpmk42: Thanks for the website. It looks like the technical articles have some great instructions on maintenance. I'm not sure if I trust myself with doing any of it just yet but at least I can get an idea of what's going on.

rs4-380: It does sound like it could just be a bad catalytic converter but this exactly why I wanted to post on the forum:
"If the engine is dumping raw fuel into the exhaust you would need to figure out why it is doing it before taking care of the cat."
I feel like a lot of mechanics will just read the code and replace the part and I want to make sure there isn't something that caused it to go bad in the first place. Thanks for the advice! At least I can ask the mechanic the right questions!

jschick: I will definitely have to do some research about the vac pump and the purge valve. I haven't done too much yet but in a quick search found this article:
http://www.motor.com/magazine/pdfs/102007_04.pdf
It sounds like I have a lot of research to do but now I know where to start! Great advice about running the car at night and looking at the cats! This is probably something that most car people know but I had no idea! I'm going to try that tonight. It could very well be the O2 sensor because it was just replaced on the other Audi and I've heard this is a common problem. The Vag-Com probably would be worth the money. I'll have to look into it.

Thanks again for the replies! I'll keep you updated.

Airbag

Sounds like lots going on here ...
Are you sure you keep getting the same code coming back ? check engine light after fill up sounds like evap system check failure as mentioned , get the codes dumped again ASAP . could be the purge soolenoid or an evap leak .. although evap leak will not cause drivability issues.

The catalytic efficiency check is telling you there is not enough difference in reading in the front and rear o2 sensor on one bank. Sounds like the rear o2 sensor is doing it's job. The rear sensor o2 failure again wiould not cause you drivability issues, just trip the light . Given you have drivability issues if youhad a bad o2 sensor I would think it would be an up front sensor. if it is not leaning out the fuel mixture it will run rich on that bank and cook your cat by dumping fuel in. If Vag com allows real time monitoring you could monitor both front O2 sensors and compare .
if youdo go the cat route make sure you replace the o2 sensors at the same time.. especially the front .. rears may be more expensive.

Zaphodb17

"Recently, the light has been going on again and it seemed to be after I got gas so I started putting 89 in it (I know...I should have been doing this before). This seemed to help until this past month when the light went on twice after getting gas."
Just a quick question...what octane have you been running in your A-6? I only run 91 or 93 and I thought that's what Audi recommended. I think there's a knock sensor on this engine, so you can run lower octane, but I'm pretty sure you'll get best performance with the highest octane you can find. Also the "weird oil (not gas) smell" you're getting is most likely the common Audi valve cover seal/tensioner/cam plug leaks that all of these cars exhibit, eventually.

Airbag

i ahve been foloeing this thread with some interest .. went to check my cam plugs and i have a leaking one 9 passenger side ) looks like a bit of a pig with some egr type valve in the way.
Also i went to inspect the vac pump ( or pcv I would call it ) > holly crap i had to take a plate off with vac lines and sensors and it was under that . it looks like it is crimped on . original ? also one end looks like it is under the intake and I would never be able to reatach even if I got it off . If this the right piece I am looking at ? it is a Y with tubes coming from the valve cover area and possibley going into the intake and T.B . Any suggestions ?
thanks

Just Me

typically, an failing 02 sensor will throw a code.

An inefficient cat will too, but a blocked one might not - it could still be *efficient*, just high back pressure. That should be easy enough for a mechanic to check....

I doubt its gas. However, i use 91+.

G