hey guys,

I keep getting this CEL code, "P0420 Catalyst system efficiency below threshold." The only thing I have done to my car is a custom local shop cat-back 2.25 exhaust with a dynomaster muffler. BTW, this is on a 96 Impreza L.
Thanks for any help.

Cody

http://www.pagetraffic.com/images/faq7.jpg

It's only really an FAQ in the context of a catless exhaust, which is not the case here if all he has is a catback.

On a 96, it's possible that the cat(s) is/are really starting to go out - or that the rear O2 sensor is on the fritz... OTOH if it started happening immediately after the catback install, then it's possible the shop screwed something up - either damaging the sensor or whacking on the cat with a BFH...

Ok Ok, your right, but I what I meant I suppose was that its probably THE most documented CEL. There are threads upon threads about this CEL, over and above catless exhaust... so much so as it could even be a loose gas cap.

Randy

Sorry Randy...I didn't even think to do a search on this code. This just started happening recently but I had the exhaust done last summer so I don't think the shop screwd up anything. So can I just gut the cat, remove it and throw in a straight pipe or what???

Sorry Randy...I didn't even think to do a search on this code. This just started happening recently but I had the exhaust done last summer so I don't think the shop screwd up anything. So can I just gut the cat, remove it and throw in a straight pipe or what???

Maybe the O2 sensor behind the cat converter got borked when the exhaust work was done. If not, search on the spark plug adaptor mechanical fix for that code usually used on staged wrxs.

So can I just gut the cat, remove it and throw in a straight pipe or what???

Only if you want to keep that code. Otherwise I would get a high flow cat. I've heard that there are someout there that wont throw the code. Honestly I'd just sit on it for a while. Mine went away after about a week. I figure it was a tank of crappy gas.

Randy

Hmm, well how much are we talking for a high flow cat? I've had this code about 5 times and it comes on for about 3 days and then disappears but this time it was on for like a week so I cleared it yesterday and it hasn't come back yet.

Put a mechanical or electric CEL fix in your rear O2 sensor, and you shouldn't get the light again.


Brian

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