So for anybody who didn't see my last thread, I have a 02 A4 1.8T, 96k miles, new timing belt, new water pump. Then after buying it, the cat went, followed a day later by the turbo. All was fixed and all was looking good until today. I brought the car to get it inspected and it was rejected for having a hole in the exhaust. I'm hoping I can get the dealer to fix it considering all the problems I've had with the car since I bought it. About an hour after getting the inspection, the check engine light came on. I brought it to Advanced Auto for a scan and they gave me code P0420, and something along the lines of catalyst system efficiency below threshold bank 2 (not 100% sure on bank number but thought they told me 2). Is my cat bad again, or is it a bad o2 sensor, or is it worse than that? Also, if it is the cat, what would be the downside to replacing it with a test pipe and o2 spacers?

 

update: the cel went away in its own, not sure if that's a good thing or not, and I patched the hole in the exhaust (after the cel went away). Things are looking good for the moment.

 

so u patched ur hole and then the code went away or the code went away and then u patched? Im just curious for others sake of what went first to get rid of the code.

 

Well I figured I would patch the hole before really jumping to conclusions about the cel, but on my way to fix the hole, the light went away. Also. for those who want to know, the hole was on the middle of the exhaust where one pipe goes over the other and is held together by two clamps.