Roger Stokes Posted November 5, 2010 Share Posted November 5, 2010 I have a 2001 forester and the check engine light was on went to auto zone and had it scaned and needed the 02 sensor front one so I replace it. Then 2 months later check engine came on again, had it checked and it ran a coed P0420 with 3 different causes,1 Rich A/F ratio, 2 Ignition system malifuction, 3 Faulty catalytic converter. Any advice on which on and what to do? Thanks, Roger Quote Link to comment Share on other sites More sharing options...
Blacky Posted November 6, 2010 Share Posted November 6, 2010 (edited) PO420 is "THE" most common code. There's a multitude of things which will trigger it. I just clear it with my code reader and it usually does not come on again for many, many months. Definately do not get sucked into replacing your cats. It will not stop the code from coming up and it will cost you a small fortune. Edited November 6, 2010 by Blacky Quote Link to comment Share on other sites More sharing options...
Fairtax4me Posted November 6, 2010 Share Posted November 6, 2010 Do you still have the old O2 sensor? What brand was the new one? Quote Link to comment Share on other sites More sharing options...
OB99W Posted November 6, 2010 Share Posted November 6, 2010 [...]needed the 02 sensor front one so I replace it. Then 2 months later check engine came on again, had it checked and it ran a coed P0420 with 3 different causes[...] As Fairtax4me is (I think) hinting at, if the front sensor wasn't a Subaru OEM one, that might be possible cause number 4 . Quote Link to comment Share on other sites More sharing options...
Fairtax4me Posted November 6, 2010 Share Posted November 6, 2010 As Fairtax4me is (I think) hinting at, if the front sensor wasn't a Subaru OEM one, that might be possible cause number 4 . Bingo! More than likely, the P0420 code is the result of readings from the new sensor. Search P0420 and you'll find a thousand threads about it, and plenty of info about what to do to remedy the cause. Quote Link to comment Share on other sites More sharing options...
idosubaru Posted November 6, 2010 Share Posted November 6, 2010 Is it the same code that you had the first time or do you not remember? Exhaust leaks, even small ones, can also cause this code. Quote Link to comment Share on other sites More sharing options...
zacyork Posted November 6, 2010 Share Posted November 6, 2010 aftermarket o2 sensors can give you problems. i would recommend finding an oem sensor. also some are heated o2 sensors and some arent. try putting in your old one and see if the new codes go away Quote Link to comment Share on other sites More sharing options...
Roger Stokes Posted November 9, 2010 Author Share Posted November 9, 2010 Yes it was a Subaru brand Quote Link to comment Share on other sites More sharing options...
idosubaru Posted November 9, 2010 Share Posted November 9, 2010 folks may ask if it was bought from Subaru or just a "Subaru brand" from an aftermarket store. no exhaust leak? Quote Link to comment Share on other sites More sharing options...
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