Acid bath and P0420

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by sorka, Jun 7, 2016.

  1. sorka

    sorka Active Member

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    Was getting the cat below threshold code after each startup. I must have reset it 40+ times over the last 6 months.

    I decided to try the Oxalic and Citric acid bath this weekend (0.1M of oxalic acid + 0.1M of citric acid). Let the cat soak for 6 hours with occasional agitation. I was going to use a pump but the darn thing was broken so I just agitated the bucket every 30 minutes or so.

    Re-assembled and started car. Within 5 minutes of driving, all the emissions startup cycles went green:

    [​IMG]

    Previously it would take 20 minutes before catalyst would complete and then I'd get an engine check light. So I took this as a very good sign.

    However, this morning, after the car sat all night, I started it and the emissions showed ready immediately right at startup. So then I let it sit again today for 5 hours and start it up and still everything comes up ready immediately again. Is this normal?
     
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  2. JC91006

    JC91006 Senior Member

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    How can the Catalytic converter be taken off and soaked? Isn't it a long pipe all attached together?
     
  3. wjtracy

    wjtracy Senior Member

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    Cool...how'd you get the cat off?
     
  4. sorka

    sorka Active Member

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    The cat is at the very front of the pipe so you only need about 14" of water.
     
  5. sorka

    sorka Active Member

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    4 service ramps to elevate the car, an O2 sensor wrench(I'd just replaced the O2 sensor a few weeks ago with no luck), a 14mm socket and extension of at least 12" and preferably a 1/2" driver and a breaker bar.

    Removing the entire assembly is about a 5 minute job assuming you don't have to deal with a frozen O2 sensor. My old o2 sensor from a few weeks ago was seized and I had to let the threads soak in PB blaster for a few hours before it broke free. Didn't want to risk breaking off the O2 bung by over torquing with the breaker bar.
     
    #5 sorka, Jun 7, 2016
    Last edited: Jun 7, 2016
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  6. JC91006

    JC91006 Senior Member

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    You're right! The 2nd one doesn't need soaking as it's not the one that fails.
     
  7. S Keith

    S Keith Senior Member

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    Normal. That's the since DTC screen. It's showing status since DTC reset. Once they go green they stay green until a fault or reset. You need the current drive cycle status screen.
     
    #7 S Keith, Jun 7, 2016
    Last edited: Jun 7, 2016
  8. sorka

    sorka Active Member

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    Well that makes sense since the error hasn't returned. Note, resetting the fault doesn't clear the status then, just the the codes.
     
  9. S Keith

    S Keith Senior Member

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    Disconnect your 12v if you want to see what it does after a full reset.
     
  10. sorka

    sorka Active Member

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    Just drove another 140 miles. Still no P0420.
     
  11. Patrick Wong

    Patrick Wong DIY Enthusiast

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    What did the acid bath look like after you removed the cat? How many gallons of water were used with the two acid products?

    Excellent outcome, congratulations!
     
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  12. sorka

    sorka Active Member

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    Not celebrating until I smog the car next month when I get my renewal notice.

    I basically followed this video:



    and produced 8 gallons of solution for the size of container I had.

    The fluid was a dark green. The cat was not clogged prior but it was coated with ash that did not come off flushing with water.

    I burn about a qt of oil every 5K miles.
     
  13. S Keith

    S Keith Senior Member

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    Can you run a smog check early? Your car is clearly ready.

    Whatever the outcome, it seems clear you've improved it. More driving and oil burning is only going to work against you. It might make sense to park it until you get the letter.
     
  14. sorka

    sorka Active Member

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    I think the amount of oil being burned is small enough that it would take a 100K miles to ruin a new cat. Reg is due on 9/22. I should get the renewal notice next month. Smog is good for 90 days but I'm not sure if that's only for selling. I thought about doing it exactly 90 days before the due date which would be around the 25th of this month.
     
  15. JC91006

    JC91006 Senior Member

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    Smog check certificate are good for 90 days in California
     
  16. wjtracy

    wjtracy Senior Member

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    I hope you're OK...on the TPMS it takes a week or so for the system to catch up
     
  17. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Or, to be more precise, although the second cc may fail, the engine ECU does not have a downstream O2 sensor to determine the second cc status to be good or bad.
     
  18. JC91006

    JC91006 Senior Member

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    I didn't ask the OP if he was in CA with under 150k miles on his 2009? Cause if that's the case, the car would still be under warranty for a new Cat
     
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  19. sorka

    sorka Active Member

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    CA but 223K miles.
     
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  20. S Keith

    S Keith Senior Member

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    I haven't tried it on the prius, but on my civic hybrid with P0420, I could monitor the downstream O2 sensor with a torque pro graph and see it smoothed out very nicely after I replaced the cat. If you can do the same on the prius, I would be confident in the results.
     
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