P0420 light has been coming on and off intermittently and now it's state inspection time. Help?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by ediblestars, Dec 15, 2020.

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  1. ediblestars

    ediblestars New Member

    Joined:
    Dec 15, 2020
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    Location:
    Massachusetts
    Vehicle:
    2008 Prius
    Model:
    N/A
    I have a 2008 Prius. In August 2019, I was driving across the country when my check engine light came on. I had it read, and it was P0420. Learning that it likely wouldn't cause harm to the vehicle itself, I shrugged it off, kept driving, and decided I'd deal with it when it came time to get my state inspection.

    Throughout that winter and the summer/fall of this year, a curious thing kept happening. The CE light would come on, stay for a while (a few days to a couple weeks) and then turn off again. This has happened on and off for over a year now. It seems like it may have some correlation with changes in temperature, but I can't be sure. And now, the can I kicked down the road is upon me--I need to get my MA state inspection.

    Throughout the year, I've tried to find instances online of the CE light coming on and off for a P0420 code and haven't found much. Does anyone know if the intermittence of the light might indicate a particular cause? I know the catalytic converter is the most likely culprit for a P0420, but I'm wondering what the on-and-off occurrence signifies, if anything. Could it be an O2 sensor instead? Does the cat vary in its compliance with emissions standards, causing the light to come on sometimes and turn off other times? Could it jostle around and get knocked into and out of alignment?

    Most crucially, what should I do for my inspection? Most recently, the CE light was off for many weeks, and then turned on last Thursday. It turned off again yesterday. My initial thought was to go get the inspection now before it turns on again, but reading up about the emissions inspection procedure, I'm not sure if that would cut it. Is there any way I can time things so I'd be likely to pass? If it stays off for a few weeks and lots of travel, would that make it more likely to pass? Would getting an oil change beforehand help? I'm nearly due for one.

    If it's relevant, my battery ran out and I needed to get a jump a week ago on the night of Sunday the 6th.

    Thanks in advance for any help! I know very little about cars, so I appreciate any assistance.
     
    #1 ediblestars, Dec 15, 2020
  2. SFO

    SFO Senior Member

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    Location:
    Northern California
    Vehicle:
    2007 Prius
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    Welcome to PriusChat!!

    How many miles on the vehicle?

    When was the 12v last replaced, and how many hours per week are you driving? (12v batteries don't last forever)

    Have you checked the dealer maintenance by entering the VIN at : Track Your Service Records with Your Toyota Owners Account

    Best to reread the OBD2 codes (DTCs) again by finding or purchasing an OBD2 code scanner, many here prefer a 'mini-vci' cable and a copy of techstream (dealership technician software) installed on a windows device. Others get by using an OBD2 bluetooth adapter and an App like Torque or Dr Prius.

    Depending on the mileage and the level of oil consumption, it might be time for a new CAT, not that expensive for an aftermarket cat , which I believe is allowed in MA(?), and then you could sell your used OEM for 1k+ on fleabay or locally.
     
    #2 SFO, Dec 16, 2020
  3. davecook89t

    davecook89t Senior Member

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    Location:
    Washington State, Florida
    Vehicle:
    2017 Prius
    Model:
    Four Touring
    Just for the record, our Gen 2 has been doing the same thing as yours for the last month or so (CEL on occasionally, with the P0420 code). Since it is registered in Florida, with no inspection requirement, and has 291k miles and will soon be retired, I'm not going to do anything about it.
     
    #3 davecook89t, Dec 16, 2020
  4. edthefox5

    edthefox5 Senior Member

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    Location:
    Clearwater, Florida
    Vehicle:
    2007 Prius
    Model:
    Two
    based on what your saying the car probably has high mileage don't know never listed my guess is the engine eats oil bad and oil level is very low now that's why the CEL is on and off very common on here and that oil eater motor has fouled the cat. That's very very common.

    The bad news is your a carb stste and not sure if like California they are as strict as they are so requires an OEM cat only. You better hope not as the stock cat is $1551. + install.
    An after market cat is $129 if there not picky plus install.
    I believe Mass is that picky as I just sold my cat on ebay for $1350 to a guy in Mass.

    STOLEN Cats are a big post on this site as California G2 owners are getting there cats stolen left and right. There worth alot of money.

    Go on youtube and search:

    Prius Stolen

    Then use the search forums link up top and search:

    stolen
     
    #4 edthefox5, Dec 16, 2020
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