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Help.. PO420 Exhaust code..

Well the ugly Check Engine Light came on again. It came on for about a week a year ago, got it checked and it was the PO420 code.. "Catalyst System Efficiency Below Threshold (Bank 1)." After a few days it shut off, so I didnt think much of it. Now it came back on a few weeks ago, same code, and isnt going off. The guy at Autozone says its my O2 Sensor. Makes sense cause ive been getting crap gas mileage.

Could it be the O2 sensor? The car has a Bassani Hi Flow pipe on it. Im alittle confused.. I dont know if my Cat is bad, the O2 sensor is bad, or if its just one of those common things. Any opinions?

Thanks,

-Franklin '96 Cobra

Reply to
WhyteStang
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Faulty CTS, high fuel pressure, cylinder misfires, retarded timing..... these are all conditions that can also set code P0420.

HTH

Reply to
Jim Warman

Sounds like that HO2S to me, bank 1...

P0420 - Catalyst System Efficiency Below threshold condition: Engine running at steady state highway conditions for 5 minutes in closed loop, then the PCM detected that the rear HO2S switch rate was too high.

G'luck

Brandon

Reply to
indi

Ok, but on a '96 Cobra, there were 4 oxygen sensors.

The Bassani probably eliminated the rear two... but now they are replaced by eliminators.

Maybe one of the eliminators isn't working correctly?

Jim, correct me if I'm wrong, but the front O2 sensor measures the before picture, the rear measures the after picture. If there's an eliminator on it, you're basically tricking your computer into thinking that the cat's doing just fine.

Hope this helps in some way...

JS

Reply to
JS

Ahh yes that's right. The second pair of O2 sensors is there to monitor the efficency of the Catalytic Converters. After re-reading that p0420 explaination it makes a lot more sense.

BUT as you noted if the Bassani eliminates the rear two O2 sensors and eliminators are installed... then I have no clue how the p0420 code is being set, maybe a short? But I am changing my previous assesment to the Catalytic Converter, if in fact there is the rear 2 O2 sensors... :) Am I allowed to do that?

Does any of this rambling make any sense? It is kind of late...

Brandon

Reply to
indi

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