Need Help understanding TechStream - P0420 Code with screenshots

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Captain Serious, Jun 24, 2019.

  1. Captain Serious

    Captain Serious Junior Member

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    Hello,

    I have a 2008 Prius Touring that's showing a P0420 code. P0420 means "Catalyst System Efficiency Below Threshold". My understanding is that this could be caused by the Catalytic Converter itself... OR... one or both of the O2 Sensors.

    I tried using TechStream to narrow down the possible causes, but I don't know what I'm looking at. I was expecting the software to jump out and say "hey pal, this is the problem".

    Below are some screenshots of what I though would be relevant information. If you know what you're talking about and need more parameters or can tell me what to go look for, I would appreciate that advice.

    I do not know what to check next to determine if it is the Cat (expensive) or O2 Sensor (less expensive).



    Here is the Cumulative Monitor showing Catalyst Efficiency Failure:

    Cumulative Monitor.png



    Here is the Current Monitor showing the same thing:

    Current Monitor.png

    Clicking on the magnifying glass icon in the above graphic shows the following:

    O2 test results.png
    How is the "Test Value" calculated? This would point me in the right direction.


    This is all of the engine parameters when the engine is running:

    DataList.png



    I tried using the Graph Function but it was not working. It would show the below real-time values but not show a graph:

    Trying a Graph.png



    I'm looking for help on what to do next to figure out which part is causing the P0420 code.

    Thanks in advance!
     

    Attached Files:

    #1 Captain Serious, Jun 24, 2019
  2. exstudent

    exstudent Senior Member

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    Techstream is to just retrieve codes, diagnostics, and do maintenance. The factory manual provides the trouble shooting tree for the codes.

    How many miles on the odometer and how much oil does the car burn between oil changes or very 1,000miles? If the car consumes a lot of oil, that will kill any catalytic converter quickly! You would want to address the oil consumption before replacing the cat and O2 sensors on such a car, otherwise, you will end up in the same position soon.

    Exhaust in good condition? No damage to the catalytic converter? No rattling sound heard?

    Assuming the wires leading to the front and rear O2 sensors are in good condition (not damaged by road debris or creatures chewing on the wire), it could be the O2 sensors are bad, and/or the catalytic converter is bad. You can check the voltage coming from the O2 sensor; if it is out of specs, replace. See this post: P0420 & TechStream - Troubleshoot O2 sensors? | PriusChat
    Link to a Desno PDF trouble shooting guide for O2 sensor.

    The OEM catalytic converter is expensive b/c it contains a lot of catalyst. After market catalysts are cheaper b/c they contain less catalyst. Price is directly proportional to amount of catalyst, amongst other things. OEM is CARB certified to perform within the manufactures specifications and come with a 5 year emissions/performance warranty. Aftermarket cats are NOT CARB certified b/c they don't want to pay for testing, and they don't want to offer a 5 year emissions/performance warranty.
     
    #2 exstudent, Jun 25, 2019
    Last edited: Jun 25, 2019
    Dxta likes this.
  3. Skibob

    Skibob Senior Member

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    One word of advice. If you do decide to change the o2 sensors stick with either Toyota Factory or Denso (Toyota Factory). Other cheaper brands have been known to cause problems and they sell the Denso’s on Rock Auto.
     
    #3 Skibob, Jun 25, 2019
  4. Captain Serious

    Captain Serious Junior Member

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    Thanks for the response. The car just hit 150k miles.

    I have a slight oil consumption issue. I replaced the PCV valve not long ago and it got better but still requires some topping off between oil changes. I don't have actual quarts-per-mile data for my oil consumption. Do you know of a specific Oil Consumption Troubleshooting post? I've looked several times and found people with that problem, but haven't found a good reaction plan. Replacing piston rings is probably not going to happen.

    I need to read and digest your linked P0420 thread. I'll report back in a couple days. Thanks.
     
    #4 Captain Serious, Jun 26, 2019
  5. exstudent

    exstudent Senior Member

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    I was mistaken. I could have sworn seeing an approximate consumption rate for a given mileage range in the Owner's Manual.

    It is well known here that as the engine seems to cross 100k miles, the consumption goes up. People who don't check the engine oil level regularly, and wait for the low oil (aka no oil) pressure warning light, or the intermittent master warning light (red triangle w/ exclamation point) when they brake hard or take a turn hard, experience accelerated engine damange/wear. You hear of some crazy engine oil consumption rates like 1quart/700miles!

    I am at maybe 1/4 - 1/2 quart every 5k miles. 158k miles on odometer. Had the car since new and have religiously checked engine oil level.

    Most people who have a horrible engine oil consuming engine, either get rid of the car or swap in a used lower mileage engine. I am not aware of anyone doing a teardown and rebuild; maybe too time consuming and/or beyond their skill/comfort level. This would definitely be a good learning project though.
     
    #5 exstudent, Jun 26, 2019
  6. Dxta

    Dxta Senior Member

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    I have done a teardown and rebuild of both Prius and Camry hybrid engines.
    If you got the time, the engine can be rebuilt.
     
    #6 Dxta, Jun 26, 2019
  7. exstudent

    exstudent Senior Member

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    Depending on what your plans are for the car (get rid of soon - keep a few years - keep till the wheels fall off), should dictate your next steps.

    If you decide on a weld on universal aftermarket cat, I am aware of one person who reported back that it lasted a about a year. Something to keep in mind.

    A new OEM part is pricy:
    $1492.70, Discount Parts Monster, might be a reseller of Toyota OEM parts?
    $1520.34 Gulf Freeway Toyota Auto Nation, shipping extra.
    $1686.20, Camelback Toyota (Phoenix, AZ); unlikely this part would qualify for free shipping due to size and weight.

    Search w/ evil Google, Yahoo, Bing, etc: "Toyota OEM part 17410-21500" to find other Toyota dealers who sell online at a discount compared to their retail parts rate. There might be a dealer near you. Also, call deales to see if they will match the cheaper online prices you found; some will, some won't. Asking just costs you a few minutes and can only help your wallet if they say yes.

    Autodismantlers and junkyards might be another option.
    This one offers a one year warranty on all their parts. You have to call for pricing & shipping. 2008 Toyota Prius exhaust pipe - 17410-21500 - Used - A Grade.
     
    #7 exstudent, Jun 26, 2019
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