Hey guys I have a 2003 A4 quattro 3.0 6 speed manual etc etc. I have to pass emmissions and i have a bad cat producing error code p0421.

I get the p0421 immediately when monitor finishes. Not only that but a little later on I get p0431 which is the other cat. I may be lucky and get away with replacing one.

I think in connecticut you can get away with 1 monitor blinking while the others are set.

On reset I have the cat blinking and secondary Air System blinking on obd2. I dont' think anythings wrong with my SAS but I can't get the monitor to set at all(No DTC for it... yet). If anyone can help me with a procedure to get that set before the cat that would be amazing. I hear about drive cycles and what not for every other car. But for some reason any audi procedures seem to be illuding me. I'm praying someone here has some experience. Other wise I'm out 2 grand.

Time is a factor also, I'm already late for emissions. And i found out in my old car you can get ticketed for not getting them done so I'm trying to avoid! Help help!

 

as a temp way to pass only, if you have access to the O2 sensors after the cats, take them out the cat and zip tie it somewhere and plug the hole in the cat. this will fool the ecu thinking the cat is fine. or you can get 2 18mm spark plug defouler and drill one all the way through so the O2 sensor can be screwed into that, and then take the other defouler and screw it on top of the drilled defouler and then put this back into the cat.

this removes the O2 sensor from the exhaust stream thus reading differently than the primary O2 sensor, so the ecu thinks the cat is working fine.

 

I guess I can try it. I haven't a whole lot of experience with getting to that region but I can try! Do I do both Precat and Post cat sensors or just one of them?

Also I was reading up on Vag which I don't have but I've been considering buying(while expensive it sure as hell beat 1-2 grand. Was reading that vag has a procedure for forcing readiness. I emailed Ross Tech to see if it was possible to accomplish this on my car but I haven't received a response yet.(It was only 6 hours ago but every minute feels like a life time when you inch closer to having to replace your caty XD)

 

on a 3.0 would he not need two spark plug foulers? I had purchased on eof those off a sit and it didnt get rid of my p0420. But ive never tried the autozone ones yet. I might have to try it.

 

maybe the sensor was bad then? did you clear the code and it came back?
you need 2 for each cat, so 4 total.

and Lee Clark, only do post cat. doing the O2 sensore before the cat will make your car run rich.

O2 Sensor modification using spark plug non-foulers

 

Howdy. I have a 1.8t but was having similar issues. Try the post cat spacers and if you have to heat them up be gentle unless you are replacing them. As for the im monitors I was a bit confused, after a bunch of drive cycles and almost 70 miles my sec air and evap were still not ready. This is what earned my fellow grease monkey a bottle of good scotch and myself a nys sticker ...fill the tank with gas, clear the codes and disco the battery for a while. Start and let the car idle a bit, do a few miles of city driving until things are warm and then bring it up to around 65, slowing down to 40 a few times downshifting . Park the car, let it cool off and repeat. It might sound silly but after 3 times and about 26 miles all monitors were ready...Good luck !

 

Hey guys thanks for all the posts. I guess I'm going to try the spacers. Although I'm not exactly sure how I'm going to do it as I don't own a drill XD but we shall see. I just put down 250 for a vag hopefully that helps too. I'm hoping that purchase wasn't a waste of money. Seems like beyond what I'm trying to do it is an essential tool.

 

Because I've never done it before is getting to the 02 sensors pretty simple of I have the rear of the car on jack stands? I've never tried it before, usually I pay someone to do those, have I been wasting my money all these years?

(I already found out I wasted $140 paying for clutch sensors to be changed, which they did wrong and I had to do myself and it literally only took me ten minutes constantly looking back and forth between haynes manual and the work. Never going back to those scum bags)

 

its a brand new sensor. im thinking it was cuz it was from ebay. lol. Ill have to try to other route but im leaning towards a hfc in the very near future!

 

Does anyone know a DIY with pics for replacing downstream 02 sensors? I'm sorry if this is a ridiculous request for experts, but this is my first audi and the only work I've done so far is brake caliper replacement