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#1 2019-09-24 16:23:21

Paul C.
Registered: 2019-07-25
User Number: 46533
Posts: 29

Trouble Code - How to fix

       The Check Engine light on my 2005 92x illuminated. I used the code reader from the local Auto-Zone store and got code PO 420 which going by the Haynes Impreza manual is "Catalyst system efficiency below threshold (Bank1)". Does anyone know what this actually means and/or what I should be looking for or doing to "fix" the problem? I am going to try adding something called Cat Clean which is available at Advanced Auto as I'm told that cleans injectors and the Catalytic Converter. Appreciate any help and/or advice.



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#2 2019-09-24 16:34:56

Sooper Genius
From: SF Bay Area, CA.
Registered: 2005-06-04
User Number: 158
Posts: 4536

Re: Trouble Code - How to fix

I'm going back a ways but if memory serves that could be the cat itself, but could also be one of the two oxygen sensors.  There is a sensor at each end of the cat and the readings are compared to see that the cat is actually catting, as it were.  If both sensors read close enough to the same it assumes that the cat is no longer functioning efficiently.

A Real Saab and a LeMONS Saab - 1978 99 Turbo and 1979 900 Turbo
A non-SAAB - MV F4 312R - Once, the most mental bike ever made
Jaguar F-Type V6s w/6MT - commuter | 1991 Miata w/Hard top - toy
2005 9-2X Linear --> sold | Volvo C30 R-Design 6MT --> sold



#3 2019-10-18 16:33:12

accept no substitutes
Registered: 2014-11-30
User Number: 25881
Posts: 504

Re: Trouble Code - How to fix

it could be a few things but no way to know without considering all the related things:
- rear O2 sensor is actually what's feeding the ECU with that data. Replace that sensor with a new correct OEM one.
- the engine's running performance, if not correct, could be fouling the catalytic converter. doing a tuneup could help if done correctly.
- it *may* be possible to clean/wash the catalytic converter, I've seen people do this. definitely labor intensive though. you could also try a seafoam treatment of the engine
- replace the catalytic converter. a used OEM one would be your best bet, they are just hard to find. try craigslist, local facebook groups, etc. A junkyard will not sell a used catalytic converter



#4 2019-10-29 16:01:06

From: Ann Arbor
Registered: 2005-11-16
User Number: 897
Posts: 2382

Re: Trouble Code - How to fix

Did you fix it?

I just replaced my O2 sensor and did the cat w/ something aftermarket from Bosal.

I'd claim it was quick and easy, but that would be a tiny lie. 

Of course, now I have an exhaust leak further downstream probably due to me beating the living snot out of the flange between the downpipe and mid-pipe.  eek



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