Exhaust question

Q&A: Technical Support
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by Zapp_Brannigan » Wed Jul 22, 2009 10:32 pm
Well here goes..my long and arduous history with this POS.. replaced my rear o2 sensor cuz it died. Then my cat plugged up..replaced it with a magnaflow unit, 2.5" I believe. Ever since I've had a p0420 "catalyst efficiency below threshold" basically not performing up to par...Replaced front o2 with known working unit.. code still remains...I'm just wondering WTF is going on..I WANT THIS CODE GONE, just tired of it being there. Took off manifold, new manifold gasket/downpipe gasket...Can't hear any exhaust leaks...so what the hell?? Do I have to use an OEM cat for an S-series? I see many many people have used aftermarket cat's and have not had the same problem as I do.
Any input anyone??


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Joined: Sun Oct 15, 2006 10:44 am
Location: B-town, ON
by Viperoni » Thu Jul 23, 2009 6:53 am
Either the magnaflow cat isn't cleaning properly or the rear o2 isn't reading properly and causing that code to get thrown. I'd probably point a finger at the cat though.

Here's an idea, drive the car hard for 20-30 minutes to get the cat real hot. The SES light should be on for that code. Then reset the computer, and see if the light comes on. That way your light is not staying on from when the car was cold and the cat wasn't filtering as well.
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