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P0420: How to diagnose origin of problem

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Gabriel Teixeira, Feb 19, 2016.

  1. Gabriel Teixeira

    Gabriel Teixeira Junior Member

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    My 282k miles 2006 Toyota Prius is throwing code P0420 and I want to check what could be the culprit. Indeed changing the catalytic converter probably will solve the problem, but besides this costing $2000 this may not be the root of the problem. I was concerned if a faulty O2 sensor could be making the car to run rich and this eventually burned the catalytic converter. How could I diagnose that? Besides, what could else be checked?
     
  2. S Keith

    S Keith Senior Member

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  3. Gabriel Teixeira

    Gabriel Teixeira Junior Member

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    Actually I don't know if the cat was changed before since I bought the car recently (It belonged to a Uber driver). I'm pretty sure that I will change it, but I want to know how to check if something else must be verified to avoid fouling the cat again.
     
  4. exstudent

    exstudent Senior Member

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    Highly unlikely CAT was every changed.

    Death of the CAT is most likely due to the engine burning oil. This is common in Gen2 Prius, w/ high mileage. If you are not checking the oil level on a regular basis, start now. Too many posts of people never doing this, causing premature engine death due to insufficient oil, resulting in insufficient oil pressure, producing metal on metal wear.

    If you ever see this warning light, shame on you. This is an oil pressure warning light. IT IS NOT A LOW OIL LEVEL LIGHT.
    Low Oil Pressure Warning Light.jpg

    Try to find a muffler shop to cut off the bad CAT, then weld an aftermarket CAT in its place. Aftermarket CAT is $100.

    $1336.25 for a genuine OEM Toyota CAT. 2007 Toyota Prius Parts - Camelback Toyota Parts - Genuine OEM Parts - Free Shipping Its a direct fit, bolt on. You will have to contact Camelback Toyota to see how much they charge for shipping.

    Maybe a road trip down South?
    $1357 at San Bernardino Toyota. 2007 Toyota Prius Parts - Toyota of San Bernardino Online Parts Store
    $1357 at North Hollywood Toyota 2007 Toyota Prius Parts - Discounted Toyota and Scion Parts and Accessories
    Or call your your local Toyota dealers to see if they can beat/match these Toyota dealers.
     
  5. Gabriel Teixeira

    Gabriel Teixeira Junior Member

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    I can't fit a aftermarket CAT in California, it is illegal and car will be failed on visual inspection, even if producing low levels of pollutants.
    I never let the oil pressure warning light to show up, but I can't say about what the former owner did.
    If the CAT is just coated by burnt oil, removing and washing it may also restore it to life, right? I put a additive called Cataclean that, even if it didn't eliminated the P0420 code as I expected, improved the gas mileage by about 2-3 MPG, thus I assume it may be a bit clogged.
     
  6. exstudent

    exstudent Senior Member

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    Yes. CA and NY don't allow for weld-on aftermarket replacement CATs. I have never had any Smog Check station ever inspect the exhaust system, esp looking closely at the CAT. Who's to say you didn't buy the car like that, unknowingly?

    If you regularly check the oil level, in any car you own, and top off, you will likely never see that oil pressure warning light. Now a catastrophic engine component failure due to wear or impact from road debris, can cause sudden loss of oil, producing a low/no oil event, resulting in low/no oil pressure.

    I am not aware of a CAT being washable.

    All the products that claim to clean/restore a CAT have opinions on both sides: works/doesn't work. I have yet to see any maker conduct a controlled test to back-up their claims. Read this for yourself to decide if you are throwing money away. Cleaning additive can't restore a failed catalytic converter - StarTribune.com

    One tank of gas giving you a 2-3MPG improvement, is too small of a sample to celebrate. If you saw this same 2-3MPG improvement, for each of the next 5 tanks, then you can celebrate. One tank could be a fluke.
     
  7. Chuck.

    Chuck. Former Honda Enzyte Driver

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    P0420 can be raised on any car and means a problem with your emissions system.
    • the catalytic converter itself
    • O2 sensors
    • any leaks in that system
     
  8. Gabriel Teixeira

    Gabriel Teixeira Junior Member

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    Prius just required smog starting from 2015 here in California, so I was the first to have to smog it. I took a look to the cat to see if it was replaced. It had (T) GD3 etched. (T) is the Toyota logo. So I can assume this is the original catalytic converter right?

    I never topped off the oil in any car I ever had, although I expect I eventually will need in this Prius.

    I saw a video produced by Scotty Kilmer (link) where he recommends to soak the catalytic converter overnight. Some other people also recommended this online. It may not work, but still is another opportunity to save $1500.

    The car has improved consistently since. It was doing 42-45 MPG and now it does 45-50 MPG for the last 2000 miles. The engine also appears to have improved the power and smoothness a little bit. It has done that with gas for many sources like Chevron, Shell and other very cheap gas stations.

    I tried to use the Torque App with a Bluetooth OBD2 adapter to read the O2 sensors voltage and the results were very weird. I even posted in Mechanics StackExchange (link) to question if the app or the OBD2 adapter could not be working. Do you have any idea of what could be?
    I could not find any obvious leak in the system, and I could not yet check the catalytic converter itself, since the O2 voltage readings were weird. I will first confirm if the adapter is not working before taking any conclusion if the O2 sensors are bad.
     
  9. exstudent

    exstudent Senior Member

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    Don't know if those markings belong to the original CAT; never had to look at the CAT that closely. Perhaps inquire at your local Toyota parts department?

    Did you not expect this high mileage Prius, to require replacement of various wear parts? You are aware that nothing lasts forever, esp if it is being used? It may very well be that the CAT is actually worn out: the metal(s) Platinum, Palladium, and/or Rhodium are depleted.

    Penny wise, pound foolish. Lets see, pour a gallon of Pure lacquer thinner into a half filled gas tank. Drive 150miles. Rev the car to 2500RPM for 30min. Something tells me the rubber bladder, inside the North American Prius gas tanks, will die an early death. Your car, your money, do as you want.

    Soaking the CAT in soapy water, overnight, seems less damaging. If the

    Your "cleaning" thoughts assume that the CAT is not damaged and the precious metals are not depleted. If this is the case, no type of cleaning will revive a dead CAT.

    If you are crying about a CAT replacement, what are you going to do when the HV Battery goes out? Try looking at an expensive repair by amortizing the cost in terms of miles. $1500/282,000 miles = $.005319/mile This repair cost you one half cent per mile.

    How are you calculating the MPG? Are you doing old math (miles driven between fill-up divided by number of gallons filled)? Are you relying on the MPG calculator display and resetting this gauge every fill-up?

    Beliefs/feelings of improved/increased power are subjective. Only a dynamometer will give an objective result; but this would require a baseline (before CAT cleaning), and a few after CAT cleaning measurements, to validate your belief.
     
  10. Gabriel Teixeira

    Gabriel Teixeira Junior Member

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    Of course I'm expecting to replace many parts at this point, I know that many components have to be fixed once a while and I fixed many things on my car already. My only trouble is to throw away $1500 for something that may still be fixed. Would you throw away a MacBook just because it had a virus and needs to be formatted? I'm not so foolish to throw away expensive working hardware, I'm ecologically conscious (mainly because I'm cheap, to be honest). If it costed $1500 to be made, so the environment must have paid a lot for that also (quarrying the minerals, welding, transport, commercial costs...).

    I have no trouble about fixing the HV battery. It is made of 28 modules of NiMH and some circuit boards, each one individually replaceable. The cat apparently is a single monolithic block, I still need to figure out how to hack it.

    I'm calculating the MPG on a tank to tank basis (old math, as you say). I also monitor the MPG calculator and it also has show improvements. The average was around 42 MPG and now it is increasing constantly. Today was showing 45.8 MPG. It is not better because I've been somewhat heavy footed the last couple weeks.

    Anyway, I have a todo list now:
    1. Use a decent OBD2 reader to check the O2 sensors
    2. Check if any oil is getting in the exhaust (measure the compression of the cylinders will do it?)
     
  11. martintoyota

    martintoyota Junior Member

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    had the same problem: the check engine light came on and the p4020 code indicated a bad catalytic converter. I'm going to try
    Cataclean as I have nothing to lose
     
  12. martintoyota

    martintoyota Junior Member

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    Hey guys, my Cataclean converter cleaner review - Worked Great! Put it in and followed the instructions. Used just 1 bottle and so far light hasn't come back on.
     
  13. wjtracy

    wjtracy Senior Member

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    Interesting thread.
    We had another thread a while back about soaking the cat converter in a solution (I forget what chemical is in it). Basically the zinc/phosphorous (ZDDP) from the lube additives needs to be cleaned off.

    I also note the mention to NY/CA not allowing after market converters, does that mean the other CARB states (OR etc) you can?
     
  14. JC91006

    JC91006 Senior Member

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    It's a soak made up off citric acid and oxalic acid. Works short term, light will come back
     
  15. SaxPriud

    SaxPriud Junior Member

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    Hi Gabriel, I know this is an old thread, but did you figure this out? I am in the same situation as you. I really want to be sure the CAT is the problem before throwing money at it. Luckily, in TN there's no inspection. But I am trying to not remove the CAT completely and do some hack on the O2 sensor to get rid of the CEL that's now on.
     
  16. wjtracy

    wjtracy Senior Member

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    If you do not have an inspection, you (1) have time on your side, and (2) you can replace with much cheaper cat from EBay. The CARB state drivers are stuck with using OEM equivelent which is ultra low emissions (expensive platinum- which us why they get stolen in Ca.).

    To understand cat performance, one approach might be measure CO and other tailpipe emissions. I have tried to measure CO from my Prius using a home CO detector and it was basically zero non-detect except for the first several cold minutes, CO was slightly over zero maybe 100-ppm. Before cat converters cars put out 6-8% CO (60,000 to 80,000 ppm). In my state I suppose I could ask the inspection guy to do an off-the-record emissions test (Prius is exempt). If I saw anything over maybe 1000-ppm when warmed up that would be a clue that when cold, it would be probably much higher.

    We do not have much data on what a P0420 means in terms of emissions. I do not know if the cat still works acceptably or not when the code it thrown.
     
    #16 wjtracy, Sep 24, 2019
    Last edited: Sep 24, 2019
    SaxPriud likes this.