mcglups Posted January 17, 2012 Share Posted January 17, 2012 In November my 2005 Subaru Legacy GT Limited with 129K had a CEL/blinking-cruise of P420, so we replaced an O2 sensor and the CEL came back 60 miles later. We then replaced 2 additional O2 sensors and for the past 2 months it has been fine. Today with 132K the CEL/blinking-cruise came back with a P420. So we replaced the secondary valve and 100 miles later things are fine. Car is well maintained, intake air-cleaner and throttle body was last cleaned at 120K and all maintenance is done on-time, car runs great. So, if the P420 comes back, should I invest the 2000 dollars to get the entire catalytic converter and exhaust system replaced, or should I just dismiss it and keep driving it for 20 more months until I have to pass my next emissions test, and then buy a new car in the fall of 2013? Besides a P420 code, what are tangible signs that the CAT is failing such that it would adversely impact the car? The car runs really good, so I'm just not sure what to do... Link to comment Share on other sites More sharing options...
SBT Posted January 17, 2012 Share Posted January 17, 2012 Good read here - Pro amore Dei et patriam et populum - Link to comment Share on other sites More sharing options...
frank_ster Posted January 17, 2012 Share Posted January 17, 2012 well .... you can get after market cat for like 100$ and gut the existing ones. depending on the condition of the cats maybe jsut a simple beating is in order .. also you can try the sea foam stuff.. i personally just run about half a gallon of wind shield washer fluid through the engine via the brake booster hose with a restricted orifice so it rund for about 5-10 min to suck the container through then give the car a good beating. if that fails replace the 3rd cat with aftermarket . or but a catted down pipe. used or what ever . Now that's thinking out of the boxer! fyi all 05 + legacy's have built in code reader Link to comment Share on other sites More sharing options...
Moderators BarManBean Posted January 17, 2012 Moderators Share Posted January 17, 2012 Are you serious about running wind shield washer fluid through the engine a la the sea foam method or is that a joke? "Bullet-proof" your OEM TMIC! <<Buy your kit here>> Not currently in stock Link to comment Share on other sites More sharing options...
Max Capacity Posted January 17, 2012 Share Posted January 17, 2012 Did you replace the front O2 sensor or the rear O2 sensor ? The code is for the front sensor 305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD). CHECK your oil, these cars use it. Engine Build - Click Here Link to comment Share on other sites More sharing options...
mcglups Posted January 17, 2012 Author Share Posted January 17, 2012 Did you replace the front O2 sensor or the rear O2 sensor ? The code is for the front sensor When the first P420 came up we replaced a single O2 sensor, I'm not sure which one it was. The next day when the P420 came back, we replaced 2 additional O2 sensors. So in total, I replaced 3 different O2 sensors within that unit of work in November. To the best of my knowledge that are only 3 O2 sensors in total, is that correct? ...Thanks for the input, and that article is great. The idea of perhaps running the car at high RPM at low speeds for a period of time in order to burn some of the carbon off the cerium metal sounds like something I can do pretty easily. Link to comment Share on other sites More sharing options...
Max Capacity Posted January 17, 2012 Share Posted January 17, 2012 3, I thought there is one in the end of the header behind the right front tire and one in the DP before the mid pipe. 305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD). CHECK your oil, these cars use it. Engine Build - Click Here Link to comment Share on other sites More sharing options...
frank_ster Posted January 17, 2012 Share Posted January 17, 2012 there are only 2 sensors on the subies. there is also a egt sensor in the exhaust but that doesn't really do much. and yes i'm serious about running windshildwasher fluid through your car its methanol injection practice they mostly use the simple -40 washer fluid with out teflon when you run a rich mixture of this it washes the chambers and valves and everything. and it heats the crap out of the cats to clean them out. Now that's thinking out of the boxer! fyi all 05 + legacy's have built in code reader Link to comment Share on other sites More sharing options...
Adoniram Posted January 17, 2012 Share Posted January 17, 2012 $3000 for an exhaust system??? I would just get an aftermarket UP without cat, and aftermarket DP. Get a stage 2 tune from Infamous Performance, and for roughly $650 you can have your problem solved PLUS an additional 40 or so HP (my guess, could be more or less) Link to comment Share on other sites More sharing options...
mcglups Posted May 16, 2012 Author Share Posted May 16, 2012 Update: Just about to hit 139K and the CEL comes on for a week or so and then it goes off for a week or so, sometimes I pull the code and it is always the same (P420 Up/Down) and the car runs fine. Mechanic is reasonably confident that in 16 months when I need an new inspection that it will likely pass an emissions test. So long story short, although I prefer not to ignore a CEL, I just pull the code and each time it is the same. /// Hoping the 6th-gen is a good car, otherwise I'm taking this 4th-gen as far as it will go! Link to comment Share on other sites More sharing options...
Adoniram Posted May 16, 2012 Share Posted May 16, 2012 Just make sure you're aware of RI inspection requirements. When I lived in California, a CEL would be an instant failure (at least in LA county). Link to comment Share on other sites More sharing options...
mcglups Posted May 16, 2012 Author Share Posted May 16, 2012 Just make sure you're aware of RI inspection requirements. When I lived in California, a CEL would be an instant failure (at least in LA county). Definately. So far, when I reset the CEL it takes atleast 5-10 days for it to come back on so when I go for the inspection I'll have very high confidence that it doesn't come on when they do the inspection. I might drive around at 5K RPM in 3rd gear for a while before just to burn out the CAT as much as possible. Time will tell! Link to comment Share on other sites More sharing options...
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