P0420 code after replacing catalytic converter, slightly overfilled oil

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by tangerino, Apr 14, 2021.

  1. tangerino

    tangerino Junior Member

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    Like many Gen 2 owners I had my cat stolen recently. I replaced it with a well-reviewed but cheap $144 aftermarket unit on Amazon (look up "Autosaver88" for the exact model) but after maybe 50 miles of driving I got a P0420 code while on the highway today.

    Around the same time I had the cat replaced I also had Meineke change my oil. They slightly overfilled it (looks like about 1/4qt assuming the distance between high/low on the dipstick is 1qt). I assumed that wouldn't be enough to harm anything, but is it possible it's damaged my catalytic converter?

    Or is it more likely it was just a bad quality unit to begin with? The Amazon seller claims it's EPA-certified but who knows. Still, it did seem to do fine for the week or two I've been using it across several trips.

    Any advice? Am I reading the dipstick correctly and is just ~1 cm above the fill line nothing to worry about?
     
    #1 tangerino, Apr 14, 2021
    Last edited: Apr 14, 2021
  2. TMR-JWAP

    TMR-JWAP Senior Member

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    That appears to be the same cat I've installed on several cars. I've had no problems so far. What O2 sensor did you have installed to replace the OEM? So far I've used only OEM as replacements.
     
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  3. tangerino

    tangerino Junior Member

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    I bought a $24 O2 sensor off Amazon as well (not OEM but also well-rated). I can't post the link yet (just hit 4 posts), but it's Amazon's choice for "Automotive Replacement Oxygen Sensors by SFY".

    FWIW I checked the voltage via the OBD2 and it looked to be working fine (IIRC, 0.8V steady) after I installed it. Maybe I could have torqued it better (just snug, not to spec). Didn't get a P0137 code so I figured it's a good one.

    By the way, I just saw on page 286 of the manual that the min/max interval is about 1.5qt:

    So a quarter of that distance above would have been about 1.5*0.25=0.375qt extra. Still probably not enough to cause damage, would it? I saw elsewhere on Priuschat that Gen1s are very sensitive to oil levels. What about Gen2?
     
  4. tangerino

    tangerino Junior Member

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    I just re-checked the oil and it's actually about a third of the way up the dipstick, so about 1.5L (1.6qt)/3=0.53qt extra. Out of a 3.9qt capacity that sounds like it could be bad :(

    I should mention too that the O2 voltages looked fine when I tested ~50 miles ago. It's possible driving the ~50 miles since then with the extra oil that something has changed... Hopefully the sensor hasn't gotten fouled up and ruined already.

    I guess I'll have Meineke drain the oil first thing (and see how much responsibility they'll take), then maybe try some Cataclean on it, clear the P0420 code, then drive some more and see if the code comes back? Hopefully the cat can still be saved.

    Here's the O2 sensor I bought now that I can post links:
     
  5. tangerino

    tangerino Junior Member

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  6. rm04

    rm04 Junior Member

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    I personally wouldn't go lower quality/ price than the Walker 16337 cat but apparently others have had success with the autosavers

    Id switch to an OEM Denso O2 sensor to see if that helps
     
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  7. tangerino

    tangerino Junior Member

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    So do you think it's unrelated to the oil overfill? I was considering opening up the intake and checking for any excess oil to be sure, like shown here:


    Would be great to know if it's just the cat/O2 sensor vs potential engine damage.

    The oil level hasn't actually changed and it's only been driven 50 miles. Presumably if it were burning oil in the catalytic converter and clogging it up, I'd see a drop in the dipstick level?
     
    #7 tangerino, Apr 14, 2021
    Last edited: Apr 14, 2021
  8. edthefox5

    edthefox5 Senior Member

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    This is a very common story on this site.

    I know that Jiffy Lube's database says the G2 takes 5 quarts.They showed me that database it looked generic not actually there's so there may be a shared database that many oil joints use. The G2 takes a little bit less than 4 quarts.

    I never ever tell them to just change the oil and walk away. I give them a container of 4 quarts of high quality oil and the oem filter.
    They always say hey it takes 5 quarts I always say that's nice were using 4 today.....at jiffy that's $21 labor.

    I watch them. Never any hilarity.
     
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  9. tangerino

    tangerino Junior Member

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    Somehow the level at the shop was reading at 1/4-1/8inch above max instead of 1/2inch. They removed about 1/8qt and now it looks like it's just below max.

    Don't know what happened to the oil I saw before. I was pretty sure I read it correctly - read twice on flat ground, wiped stick clean before, engine cold in the morning or 1hr after driving.

    Hopefully the excess oil was just a non-issue. Cleared the P0420 and going to drive it another 50 miles and see if the code comes back. Not sure if it is the cat or the non-OEM O2 sensor, but if it does keep coming back I may just try installing a spacer: Catalytic converter code(P0420)?Solution inside | PriusChat
     
  10. tangerino

    tangerino Junior Member

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    Well the P0420 code came back after <10 miles of driving, maybe a minute or two after entering the highway a second time.

    I checked the code right after I parked and saw the (downstream) O2 voltage was holding at 0.78V steady. I took it around the block at low speed and it saw it did jump around a bit to 0.72v, 0.6v, later as low as 0.41v, 0.3v. Shouldn't it be steady? I don't think I had turned the car off but it was in park briefly.

    I then also checked the cat temperature sensors and got readings around 780F and 720F for sensor 1 and 2 respectively. I read that a 30-100F difference is a good sign the cat is working. It probably cooled off quite a bit in the ~5 minutes since the code originally set on the highway. Would getting the temperature readings at that point tell me anything?

    I would normally try getting my OBD2 to record the data while plugged in on the highway to see what exactly is triggering the P0420, but I've been getting the mysterious set of "Communication lost" codes when my reader is plugged in for a bit: U0293 u0100 u0111 u0293 p0a1d | PriusChat (Maybe that's just due to my 12v being weak)
     
  11. dolj

    dolj Senior Member

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    Maybe your OBDII reader is of inferior quality.
     
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  12. tangerino

    tangerino Junior Member

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    Any recommendations for readers that would be known not to trigger these codes? I do have a mini-VCI cable I've been meaning to try once I can get Techstream installed, but I've read they can trigger similar codes.

    The reader I'm using is a cheap ELM327 clone from eBay, but I'm skeptical that's the problem, since I never actually had those U0100 etc codes using the OBD2 several times before over 3 years. After having codes read at the shop, the mechanic's reader triggered some similar codes too (unless they also used a cheap one?). I wonder if it could actually be a weak ground connection somewhere or weak 12v? or maybe a flaky connection somewhere from rats chewing wires?

    I have had some weird electrical issues where having something plugged into my passenger-side 12v caused my combination meter to go out once, but it's been fine after removing that device (think it was a 12v splitter).

    The other weird thing is the codes once appeared *after* the OBD2 is was taken out and driven a bit. I had a scare where the red triangle appeared while I was sitting at a red light. Luckily turning the car off and on brought it back into READY mode... If things get that bad again I might have to get rid of the car. Hopefully that was just a one-off.
     
  13. edthefox5

    edthefox5 Senior Member

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    Oh I missed the part where you bought a cheapo O2 sensor. That's your issue right there. Buy an OEM and you will not only have no more 420 but your butt will be sore for a few days cause the lower O2 is $142 and thats Olathe online price.

    My local Toyota bandito will charge me $189 for that just cause there so nice.
     
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  14. tangerino

    tangerino Junior Member

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    So if it is just the sensor, could I just put a $5 spacer on? (like described in this thread: Catalytic converter code(P0420)?Solution inside | PriusChat)

    Obviously not ideal but it seems like everything else would be working fine right now. I just want to get rid of the code (and not have the light on all the time so I know when something else goes wrong down the line). There isn't a way to tell the ECU to (permanently) ignore a specific code, is there?
     
  15. timespell

    timespell Member

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    Did you replace both the air fuel upstream sensor and o2 down stream sensor after replacing the cat? If you have, and the P0420 code persists, my recommendation, short of replacing the new cat, would be to cheat by installing an o2 sensor spacer. I was constantly getting the P0420 code with my original cat after replacing both up and down stream sensors and deleting the code. So I purchased an o2 sensor spacer/extender. Removed the down stream o2 sensor, screwed in the spacer/extender and screwed the o2 sensor into the spacer/extender. Never got another code a car easily passed the emission inspection. Here is the o2 spacer/extender I used. On ebay you can get two for only $6.59 with free shipping from California. But of course you also have to pay like $.50 for tax. It ships from California.

    images.jpg

    ebay item number 393147106955

    Aside from this, trying to figure out how to get ride of the P0420 code can be a royal pain in the behind! Especially when you have replaced the cat and both sensors!
     

    Attached Files:

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  16. timespell

    timespell Member

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    Also, that was with my 2004 Prius. On my 2008, I decided to go the cat aftermarket rout and bought a Canadian Cat for $99 with free shipping. They showed that it had the EPA certified. This one so far hasn't needed a spacer/extender as it has been code free so far. But I still have one new spacer/extender left just in case.
     
  17. edthefox5

    edthefox5 Senior Member

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    Emissions code is a solid always on check engine light, any other type engine code will blink. If you see a blinking check check engine light pull over.
    So unless you live in a carb state it’s no big deal.
     
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