help with P0420 , plots inside

Discussion in 'Generation 1 Prius Discussion' started by amitt, Apr 29, 2018.

  1. amitt

    amitt Junior Member

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    I have this p0420 code and check engine light, on a 2002 with 203,000 miles, ( took the HV 2 times out of the car to replace cells, it has been through some tough times with me).

    Now I need to pass emission test, but get this code, I ran techstream and see that the sensor 2 read is pretty stable at around 0.84 volt, while sensor 1 fluctuate, and I understand that this is how it should work, so what is the issue?

    I do to monitor, and see that it failed the spec for CATALYST B1 test, the max limit is 0.499, and I got 0.518 , does this mean I get too much oxygen pass the catalytic converter?

    I read that oxygen that comes pass the cat con is considered bad, but I also read that a stable sensor 2 read at high voltage is actually good, so what is my problem here if the plot looks so flat at 0.8v? I push the gas pedal all the way down in P and can't get that 0.8v go down much, it only spikes down when the gas engine shuts off and turns on again( it's a hybrid, it does that you know).

    What should I do now? the car does burn some oil maybe 2qt for 5k miles, and I bought 20w50 to reduce that, but I don't want to put it in until I understand what is this CATALYST B1 test, and why am I getting 0.518 when the max is 0.499 .

    Can you please help explain this test and what can cause this high value?


    The strange thing is that when I reset the code, the max spec suddenly becomes 0.994v instead of 0.499, is this a bug in the ECU?
    Thanks!
    Amitt
     

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    #1 amitt, Apr 29, 2018
    Last edited: Apr 29, 2018
  2. elendilmir

    elendilmir Member

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    Amitt: I'm also trying to track down the elusive P0420 code. Are those displays (the techstream) from your emisission control agency?
     
  3. Erik Owens

    Erik Owens Member

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    Oxygen storage is not efficient enough to catalyze. Your A/F sensors look good and your O2 sensor in the rear should not be switching that much. It should be almost a flat line since if the catalytic converter is doing its job and cleaning up most the HC & CO and converting in to O2 and inert gas to expel. Change that Cat man.
     
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  4. amitt

    amitt Junior Member

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    Thanks!
    I drove this morning on the highway, I attached the plots, please look at the section I marked as "highway" this fluctuation is not normal right?

    Tomorrow I will try to drive with 20w50 oil instead of the 5w30 that I have there now, do you think it may help?

    My assumption is that this problem is due to the oil burning, but maybe when the gases will be less saturated with oil, the efficiency of the cat con will improve.


    Thanks!
     

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  5. Erik Owens

    Erik Owens Member

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    No. It will not help. Jeez. The cat will improve if you replace it.
     
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  6. amitt

    amitt Junior Member

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    The problem is that even a brand new cat will be filled with oil, and pop this error after a while, it's a known problem, I have to fix the source of the problem first, not the parts that were affected.

    Also, because in CA we can't install after market emission parts, this cat will cost more than the car, in this case I will have to sell it for scrap because I can't renew the registration, is nuking the car a better option than trying to improve this cat efficiency and oil burn?

    The problem is marginal as the error pops only occasionally, I think I can be a little more creative than filling up a new converter with oil.

    A new cat is not an option, sorry I didn't make it clear before.
    Thx
     
  7. Brian in Tucson

    Brian in Tucson Active Member

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    :(:(:( If you play by the rules, you are S.O.L. You could drive it out of state and have an inexpensive cat (Rock auto) and some 02 sensors installed. S. Cal, go to Yuma, LA go to Vegas, N. Cal to to Reno, really northern Cal go to Medford. A cheap cat will run you $150, a couple sensors $110, and installation at Midas, etc. $100 to $125. Unless the poor thing is blowing white smoke out the tail, the new cat will burn it enough that the ecm doesn't set a code. No visible smoke and no codes will get you past the smog check.

    If it is blowing white smoke, it's time to give the poor thing a decent burial or sell it off as a parts car.:cry:
     
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  8. amitt

    amitt Junior Member

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    Hi Erik I have to say it sounded kinda condescending, but I know you were trying to help, so thanks for that.
    Anyway I used castrol GTX 20W50, and guess what? the code is gone, the signal from the 02 sensor after the cat is much more stable on the highway drive than with the 5w30, on the exact same highway, in the exact same route I take every day, same temp, same speed, it just looks much better.
    Don't mind the drops you see there that indicates an engine break or city drive, just focus on what the highway plot looks like because this is what the ECU is processing.

    All monitors now show "complete" and I can go to get it smoged and pass.

    So would a new cat help in this case? maybe since it would be more efficient and resilient to the oil, but this cat con is still good, it is just the engine that is throwing so much oil at it.

    I'm an engineer and I have some feel for machines, I just thought it might help since this was obviousely what screwed up the cat con, the error code and plots show that this assumption was correct.

    So, gen1 prius owners out there, what do you have to lose, if you have a p0420, just use 20w50 and see what happens, it may allow you the keep the car for extra 2 years if you are in CA.

    BTW, never use mobile1 synthetic ( I used the one for cars with "over 75k miles") oil in these cars if you never used synthetic before, it caused the oil consumption to double, and cause this p0420 error.

    Take care,
    Amitt

    55555
     

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  9. dabard051

    dabard051 Tinkerer-in-Charge

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    I am surprised that a change in oil weight would fix a P0420 fault. Perhaps the previous oil change quantity overfilled the oil sump, and that oil blow-by was getting into the exhaust stream, setting off the P0420. Gen I Priuses are finicky about no more than 3.8 qt of oil, even with a filter change. You may want to do a compression check to get an idea if your rings are worn. If I remember correctly, the NW11 engine is a low compression design, so be sure to look up the spec if you decide to do that check, and compare the right numbers. But congrats on fixing the issue! I hope it doesn't return anytime soon.
     
  10. amitt

    amitt Junior Member

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    Thanks, it will probably not last for long because the engine is worn, it just improved it a bit so I may pass the smog test and renew the registration.

    The other components in the car may not last as much as I wish, so if I can squeeze some more life out of this cat by reducing oil burn, I prefer this over filling a new cat with this oil and spending more than what the car is worth on a part that is obviously not the main issue.


    Thanks and good luck !
     
    #10 amitt, May 2, 2018
    Last edited: May 2, 2018
  11. Brian in Tucson

    Brian in Tucson Active Member

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    Good luck to you! If your readiness monitors are all clear and you have no codes, I would drive it
    directly to the smog check station. I wonder if an old school additive like CD2 or Marvel Mystery Oil would
    help free up the rings. A road trip to get it good and hot might help, too.

    It's kinda amazing that the engine is in such bad shape. I have an 02 with about the same mileage and it has no
    trouble with the local Smog Nazis. All my cars have synthetic, tho not necessarily Mobil 1, and except for the 96 Dakota
    V8 which drips some, none use a bit of oil.

    If you can get it past smog, you're right--drive the wheels off and worry about emissions next time you need to up your registration
    again.
     
  12. amitt

    amitt Junior Member

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    Yes that's what I hope for I believe I can get pass the test, even if I try a few times, the sad thing is that this car never burned a lot of oil, I used the conventional oil from the dealership since the car had 0 miles( bought new in our family), many of the times I just let the dealer do their $30-$50 oil change and call it done, once I decided to treat it nice with Mobil1 synthetic for "engines with over 75k miles", then the oil burn go so much worse.

    I read that this is a common thing when you switch to synthetic in an old car that always used conventional.

    Some of the carbon around the seals break or some sort of thing like that.

    I just want to get my carbon back into the engine, I don't care about synthetic bxxxshxxx

    The car is very comfortable. more than my gen2, it is more quite on the highway too, the HV battery is no longer reliable and I had to open it twice to change cells, so this may be the last thing I attempt with it, although as of today( fingers crossed), everything is working as it should, AC, windows, no leaks, superb car.

    My wife pushes me to sell or donate the car right now after she heard about the error going away, I just love it so much.

    I know she is probably right, I may end up with a brick if I keep pushing my luck further.

    It is ugly too as the clear coat is completely toasted on the roof and hood....

    Thanks !
    Amitt

    55555
     
  13. dabard051

    dabard051 Tinkerer-in-Charge

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    Well, of course I would NEVER suggest doing anything illegal... but if you happen to be on vacation in a less-restrictive state than NY or CA, you might be motivated by the natural beauty of your surroundings to take care of the environment, and order a replacement cat converter delivered to your vacation address... and do the cat replacement. It may buy you a couple years more of reliable Prius driving. What you want to achieve is a reliable set of passing emissions monitor reports from the on-board computers. If you choose this route, go for a direct fit cat. Your time and multiple bruised knuckles from adapting a universal into the tiny Prius space is NOT worth the few dollars difference in price. Depending on oil viscosity for a clean smog check seems a bit dicey... but best of luck, whatever path you choose.
     
    #13 dabard051, May 8, 2018
    Last edited: May 8, 2018
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