P0420 on 99% stock 2004 WRX
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This is a discussion on P0420 on 99% stock 2004 WRX within the Maintenance, service, and repair forums, part of the Tutorials & DIY category; Ok.. before anyone starts.. i have spent hours going through as many posts as i can find on this subject ...

  1. #1
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    P0420 on 99% stock 2004 WRX

    Ok.. before anyone starts.. i have spent hours going through as many posts as i can find on this subject on this and other sites..and i cannot find an answer to satisfy my needs...

    First.. having drivin with the CEL for over a year i now have to go to inspection.. so i put out $100 for the acutron scanner and determined a bad upstream o2 sensor... $238 and a few bloody fingers later the car is driving much better and significantly more power and gas mileage... CEL cleared i go to inspection and fail due to drive cycle not complete..

    so ok.. now i got the red PULL ME OVER AND TICKET ME label on my windshield and in NJ they ticket first and ask questions later banking on the fact that you will not fight a ticket.. so i got until the end of May (alledgedly) to pass...

    Now drive cycle completd and posting
    P0420 1 of 2
    Mod $E1
    Catalyst System Effecniency Below threshold bank 1

    P0420 pd 2 of 2
    Mod $E1
    Catalyst System Effecniency Below threshold bank 1


    no other codes.. and all sensors showing complete or n/a..

    Now.. from posts i have read there really is not a fix for this in the traditional sense.. i have seen work arounds and hacks and i have seen where some people have replaced the front rear o2s and the cat conv and still posting this after drive cycle completed...

    the ONLY mod on my car that is not stock is a cold air intake which i installed within a week after buying the car band spanking new in Oct 03 (during that lunar ecplise.. how cool) with 11 miles on it.. (ya.. o4 model)..
    Blew the #1 connecting rod about 6 years ago after sucking water in.. complete rebuild by Subaru (although i should have taken it to the blind down syndrom guy up the block for a better job) at 63K miles... had to shell out another 3K out of pocket to take it to a real mechanic to fix the Subaru Dealerships screwups back then..

    but still not CELs until the year i need the inspection again...

    So i'm reaching out.. i don't want to spend all that $$ that i don't have on replacing parts unless it will fix the problem for good and i want to avoid any mods that attempt to fake out the computer... can anyone help me get to the real issue? i have access to ociloscopes, and i'm not afraid to dig into the guts .

    chad

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  3. #2
    Registered User UEDan's Avatar
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    That CAI.....

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    Pro Manscaper Mikie13's Avatar
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    Sounds like a catalytic converter is failing or something of that nature. If I'm not mistaken, that's a similar code to what come up when you swap downpipes to go stage 2 and it's catless.
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    Registered User Obeisance's Avatar
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    I've read before that the exhaust gas temperature sensor in the uppipe is used to monitor the health of the catalytic converter there.... one common mod on the 2.0L engines was removing that catalytic converter and its accompanying temperature sensor (which would no longer be needed after the cat is gone). In order to keep the car from getting a CEL a 2.2 kOhm resistor is placed into the plug (bottom plug right in front of the passenger side strut tower) that the temp sensor wires went into.

    I am guessing that if that temperature sensor is not reading the correct temperature that you may be getting an error code about catalytic converter health. I would suggest a troubleshooting fix of unplugging that sensor, placing the resistor in its place, clearing the CEL code and driving for a bit to see if it comes back.

    I am not too experienced with these cars (but I have done the uppipe mod), but I hope that my suggestion is helpful.

    ***nevermind my comments, I just realized that your code is for the rear O2 sensor, right?***
    Last edited by Obeisance; 05-09-2012 at 09:57 AM.

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    Registered User etnpnys's Avatar
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    I had this problem in my 2005 Toyota Matrix XR. Long story short: replace the cats.

    Longer version of the story: I tried every single cheaper alternative prior to replacing the catalytic converters, and the problem never went away. I replaced both O2 sensors, the rear catalytic converter (my car had two, and the front one was the expensive replacement), cleaned the MAF (which I recommend anyway), cleaned the air filter (K&N drop-in). Obeisance also mentioned a resistor to bypass the cat, which I even tried after knowing that my car passed on the actual emissions measurement.

    Code always came back, and those are the same exact codes that I was getting with the car. I ended up reverting the car back to stock (even taking the headers off and putting the stock manifold back on). The problem was that the cat truly just needed to be replaced. Find somebody who will weld in a direct replacement - I'm not sure what NJ laws are, but there were specific parts that could be used in my car, even though it was still technically illegal to replace just the catalytic converter.
    "Ah, it is the fault of our science that it wants to explain all; and if it explain not, then it says there is nothing to explain."
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    hey thanks for the quick responses.. illegal to replace the cats? that's insane.. i'll have to look into that.. but it looks like that is the way i need to go.. i'd be happy to just pass inspection at this point.. so maybe i'll try the resistor 'fix' as an interm solution.. If i do find a resolution to this i'll post as detailed as i can. thanks again guys!

    chad

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    Registered User etnpnys's Avatar
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    Quote Originally Posted by ChadU View Post
    hey thanks for the quick responses.. illegal to replace the cats? that's insane.. i'll have to look into that.. but it looks like that is the way i need to go.. i'd be happy to just pass inspection at this point.. so maybe i'll try the resistor 'fix' as an interm solution.. If i do find a resolution to this i'll post as detailed as i can. thanks again guys!

    chad
    Yeah, in CA it's technically illegal to modify the emissions equipment *AT ALL*. So welding in a new cat is illegal. However, if you happen to drive 4 hours to Nevada, you can get it done anywhere, and so when you get your car smogged and the inspection reveals that there is something different, the parts that are installed have to be on an approved list on the CARB website.

    Also, the discouragement to taking the cheaper route is because it's technically illegal. But I like to play by the rules though, right? So I call up Toyota to ask them how much for a cat and they quote me $1500. SERIOUSLY. Why? Because they know they have a monopoly on that and thus refuse to sell anything except for the entire exhaust system from the manifold to the exhaust tips. Highway robbery, if you ask me, to charge somebody that much money on a simple part that is eventually going to go out. So I had a few cats welded in and it passed because they were approved parts.
    "Ah, it is the fault of our science that it wants to explain all; and if it explain not, then it says there is nothing to explain."
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    the o2 sensor was the original code that i fixed.. .. it's the new inefficiency that is the problem..

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    Registered User UEDan's Avatar
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    Its only illegal to take of a WORKING cat in California.

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    Registered User etnpnys's Avatar
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    Quote Originally Posted by UEDan View Post
    Its only illegal to take of a WORKING cat in California.
    That's what I thought, too, but nobody even wanted to talk to me over the phone about this process; they wanted to keep it on the 'down-low' and only discuss in person. And then they wanted to keep it off the books. And these aren't shady places, they're just fellow gearheads that understand the robbery that's going on.
    "Ah, it is the fault of our science that it wants to explain all; and if it explain not, then it says there is nothing to explain."
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    thepartsbin.com has a EvanFischer Parts Bin - Auto Parts and Accessories Catalog - Catalytic Converter

    not expensive at all.. any thoughts on this? i'd rather do things 'legally' or at least whatever is still 'legal' today... i'll have to research this all a bit more.. thanks again for all your input.. i greatly appreciate it.

  13. #12
    Registered User etnpnys's Avatar
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    That part looks good to me, but don't buy it based off of my recommendation. There's gotta be a smog tech somewhere here that is familiar with NJ smog laws...

    For me, like I said, I had to cross reference part numbers and executive orders against the official CARB website to make sure I had the right thing. Not sure what you need to do out there...
    "Ah, it is the fault of our science that it wants to explain all; and if it explain not, then it says there is nothing to explain."
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    ok.. went to Autozone to do a sanity check on the part.. so confirmed that it is the right part so i ordered it at that $188 price.. i'm not looking to shave time off the 1/4 mile .... just past the gov regulations.. so will post pics, etc and results as detailed as i can.. i'll say though that i expected to pay much more for the part.. and not just that.. i replaced the front pass axil last summer and it was super cheap too!.. and did all my rotors with cross drilled after market ones for less than i ever paid on my past cars.. camaro, firebird...

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    Pro Manscaper Mikie13's Avatar
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    I would have just thrown on a Catted DP and went stage 2.
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  16. #15
    Registered User etnpnys's Avatar
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    Quote Originally Posted by Mikie13 View Post
    I would have just thrown on a Catted DP and went stage 2.
    Hey, you're in NJ also!! Would that work out for him? Out here I don't think that would fly. The DP would still have to be a CARB approved part...

    But if he doesn't already have an AP he's looking at a lot more cost to go that route also, right?
    "Ah, it is the fault of our science that it wants to explain all; and if it explain not, then it says there is nothing to explain."
    -Van Helsing, from Bram Stoker's ​Dracula

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