P0420 error - what should I do?

Discussion in 'Gen 2 Prius Technical Discussion' started by enginestarter, Nov 12, 2019.

  1. enginestarter

    enginestarter Junior Member

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    P0420: Catalyst System Efficiency Below Threshold (Bank 1).
    This is what Android Torque gives.

    I had the mechanic look under the car - nothing to report, all looks fine, no part loose and cables connected OK.
    + I drove it around with the mechanic, nothing to report.

    I got the part from Eurocarparts a few months ago - it was a Klarius converter + a Bosch O2 sensor.
    I have the receipt. I can get replaced.

    Problems:

    - How do I know what is faulty? Is it the cat converter? Is it the O2 sensor?
    I'm guessing in most cases only one part is faulty?

    - I have to pay for removing the cat converter and then reinstalling again.
    The mechanic said to go and buy a new one and then he'll take off the old one, which I can then return.

    - If I don't make the right decision about the correct part - then that doubles my costs.

    What shall I do?

    EDIT: I can get rid of the error using Android Torque. It comes back after a few days. Also, sometimes (not frequently) the engine management light will just go out of it's own accord - without me doing anything. I thought I would mention.

    Thanks.
     
  2. bisco

    bisco cookie crumbler

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    would tech stream be more specific?
     
  3. enginestarter

    enginestarter Junior Member

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    what's tech stream? is that an app? i looked up on google play but couldn't see anything. let me know. thanks.
     
  4. valde3

    valde3 Senior Member

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    You can watch the values of (front) air fuel ratio sensor and (rear) oxygen sensor with running engine to determine which is faulty air fuel ratio sensor, oxygen sensor, or catalytic converter. Catalytic converter is the most likely but also the most expensive. Unfortunately it's kind of hard to explain how to read the data basically you need to see how fast signals change depending on running conditions.

    How much oil does your Prius consume? Engine oil consumption will slowly kill the catalytic converter.

    Techstream is Toyotas own diagnosis tool. There is also a cheap Chinese version of that. But many general scan tools are basically as good when diagnosing engine (related) problems like this.

    If it is the catalytic converter only legal options is to fit a new one.
     
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  5. bisco

    bisco cookie crumbler

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    yes, see valde3's response above. if you search here, you will find how and where to buy, along with advice on use
     
  6. Skibob

    Skibob Senior Member

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    You bought a Bosch front O2 sensor instead of a Denso?
     
  7. valde3

    valde3 Senior Member

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    You really shouldn't use anything other than OEM sensor as the front sensor. Front sensor is air-fuel ratio type and differences between sensors can cause problems.
     
  8. enginestarter

    enginestarter Junior Member

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    Guys, I've just been busy. I've just lived with the fault.
    I've now noticed that the car isn't as fuel efficient as before.

    @valde3, you said "How much oil does your Prius consume? Engine oil consumption will slowly kill the catalytic converter"
    Erm... it's been consuming a lot actually. Needed to top up 3 litres every 2 months - I only notice when I suddenly get red light warning when doing a sharp turning - indicating low oil.

    ALSO... I've googled around... I can't find any guides for reading the Cat converter signals. Can someone give me a link to a video?
    I'm not actually sure of the best search term to search for.

    ALSO... I saw some youtube videos, they said get a '90 Degree Oxygen O2 Sensor Socket' and fit onto the O2 sensor and this will fix the problem. Should I do this?

    @Skibob yes, I got a Bosch sensor installed. My friend worked at EuroCar part and he ordered the most expensive part (at a great discount).

    Really stuck.
    Hoping you guys can help.
    Thanks.
     
  9. dolj

    dolj Senior Member

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    Given that, you should be checking the oil once a week (eg every Saturday) and adding 1 L when the oil is 2/3's down, which going by your information would be every third week.
    It actually indicates NO oil and should not be relied upon as a warning. When this light is flashing, you should stop immediately and add 3.5 L of oil. Using this strategy, you have probably already caused damage to the engine, which only will be exacerbating the oil consumption.


    PS:
    Rather than that, you should just get your EuroCar Parts guy to source a Denso sensor that fits your car, or just go and get the correct Toyota (Denso) sensor from the Toyota parts counter.
     
    #9 dolj, Jan 22, 2020
    Last edited: Jan 22, 2020
  10. not_a_prius

    not_a_prius New Member

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    Try an Italian tune up..
    first the Cat is probably clogged up Don't replace it this is common this will burn off the carbon drive it in a lower gear DO NOT take it to red line but get it in the 3000rpm range turn off auto STOP



    SWTICH oil brands some people have good luck switching to mobil1 oil full synthetic
     
    #10 not_a_prius, Jan 22, 2020
    Last edited: Jan 22, 2020
  11. valde3

    valde3 Senior Member

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    Don't let the oil level drop! Oil pressure light tells that engine is already getting damaged. You letting the level drop has already caused engine wear and that has caused more oil consumption.

    Oil consumption is measured against miles driven not time. But that sounds like a huge oil consumption.

    With huge oil consumption there really isn't much reason to check signals from exhaust sensors. Oil consumption has almost surely caused the catalytic converter to go bad.

    You mean oxygen sensor extender? They might be illegal where you live. It will help to keep the check engine light off for some time.But eventually the catalytic converter will be bad enough that it won't help anymore. That might have already happened.

    Even if you don't care about the check engine light with high oil consumption catalytic converter will get clogged up at some point. That might already have started to happen.

    And even if you fit new catalytic converter it will get poisoned and eventually clogged by oil consumption.
     
  12. oldtechaa

    oldtechaa Active Member

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    There is no way to drive a Prius in a lower gear.
     
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