My check engine light just came on driving down the highway. Gauges aren't showing anything out of the ordinary. I noticed the past week or so, when i started my car up in the morning. It as soon as i gave it gas to drive away, it felt like it was getting ready to die. Anyone have any ideas? O2 sensors? btw. 2001 S4. tip.

 

Just had it scanned. P0421 was the code. It says cat efficiency low-bank 1. Is that the driver side? I'm hoping its just the o2.

 

you need a cat for that bank and i would suggest a new post cat oxygen sensor. and this code would not cause your car to die or almost die.. it is purely a monitor for the catalyst.. unless the cat has broken apart and clogged the exhaust.. but im sure you would be able to hear loose cat guts rattling around..

 

Na. No unusual noise. Funny thing though, I drove to the dealership to see how much they wanted for an o2 sensor for ***** and giggles. Well, as soon as I started the car up to leave the dealership, the CEL went off. There's somethin in the air around the dealership. So, I went and replaced the spark plugs today, and it runs as strong as ever. go figure.

 

P0421 is your passenger side pre-cat. It just means your downstream O2 sees "some" problem, wether is a bad O2, bad cat, whatever...

I would ignore it and not waste your money. I have no cats on my car at all, both of my downstream O2s get pissed occasionally, I just clear my codes every now and then if the CEL comes on. Unfortunately, this happens even with the vast CEL eliminators.

If it turns out your pre-cat is bad, I would suggest removing the downpipes and gutting the pre-cats all together, it makes a big difference.

 

Thanks for the input meatbiscuit. Thats gona be my next project. Exhaust work. I'm thinkin of just puttin in a straight pipe for the resonator. (that is the first muffler type thing right??) any opinions on the sound?

 

I like having a resonator, it eliminates some of the drone that you'll hear in the cab. Then again, I like the sleeper aspect of the S4 so I'm not a big fan of loud exhausts.

 

I like the exhaust note of the stock exhaust, but I just want it a little bit louder. But I don't have the money for an entire exhaust.