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P0420 engine code baffles Toyota

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by tompelletier, Oct 1, 2008.

  1. tompelletier

    tompelletier New Member

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    About a year ago, the check engine light came on on my 2001 Prius, with a P0420 code, which is faulty catalytic converter function. So I took it to Toyota for diagnosis. They said it was the engine computer needed to be updated, for about $1500, and the catalytic converter needed to be replaced for about $1,900! $3,400 total. Yikes.

    So, instead, I found a place online that sells engine computers taken from wrecks. I got the updated computer for $100 (with no guarantee, however). Took about 20 minutes to replace (it's located behind the glove compartment). Seemed to work fine, and I reset the codes, but it came back with a P0420 code.

    So instead of getting a new converter from Toyota for $1,500 bucks, I found a place that rebuilds them, and tests them to EPA certification. It's the only legal way to get a "used" converter. The cost of that was about $400, plus it cost me about $200 to have someone install it.

    Reset the codes, and the check engine light came back on again. Same code P0420.

    So after doing some research online, I changed the O2 sensors, one behind the converter, which was easy and took 15 minutes. And the one in front of the converter, which was up inside the engine compartment, and required acrobatics to get at that I didn't think I had in me. That one took at least an hour, and some pretty serious frustration.

    Reset the codes, and the check engine light came back on again. P0420.

    At this point, I was getting crazy. I called up the place from which I bought the converter. They said it's possible the converter is bad, but very rare. They are all individually tested before we ship them out. They have to be to get the EPA certification. The guy suggested that maybe the car needed a tune-up. He said sometimes when a car isn't running well, it can foul the converter.

    Now, the thing is that the car has run perfectly through all of this. Still gets 40-50 miles per gallon depending on road conditions and temperature (gets about 5 mpg better mileage in the summer).

    The only thing I could think of is that I had changed the spark plugs about six months before all this started. I didn't use Toyota plugs, but I did use brand name plugs. But I thought, we'll maybe the aftermarket ones aren't quite right.

    So I went back and bought Toyota plugs. Put them in. Reset the codes. And the check engine light came back on P0420.

    Now, I'm really reaching my wits end. And I have to get the car inspected by the end of September. And it won't pass with the check engine light on.

    So I took it back to the same Toyota dealer I started at. I explained everything I'd already done. The guy scoffed at my rebuilt converter, as I knew he would. But they tested everything and it all seems to be working correctly. The computer checks out fine. The O2 sensors read correctly. They bypassed the computer and read the O2 sensors directly and said the converter seems to be fine.

    So they are baffled. They reset the codes and told me to bring it back if the P0420 code comes back ... which it will.

    I'm just glad I didn't spend the $3400 or so they wanted me to at first, because I don't know what the problem is, but it isn't the converter, or the computer. As it is, I've spent about $1,000 and put a lot of freaking time into this, and I still have no idea what the problem is.

    And because the inspection system in NY relies entirely on the OBD II engine codes, there is no way to get the car inspected until we solve this mystery.

    Arrhhhh...

    It is at least reassuring to me that it isn't the converter or the computer. I was worried that when I took it back to Toyota, they were going to tell me the same thing they started with, change the converter and the computer.
     
    Peter R Johnson likes this.
  2. eurosteve

    eurosteve Member

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    This doesn't answer your problem but you can get away with a failed inspection in New York under certain circumstances - since you have spent over $450 in trying to repair the emissions system. You can get a waiver:

    What can occur if my vehicle fails the OBDII test?
    If the NYVIP requires a vehicle to receive an OBDII emissions inspection, and the vehicle does not qualify for a waiver (see below), the vehicle must pass that inspection in order to receive an inspection sticker. The failure of the vehicle to pass the inspection can prevent the renewal of the vehicle registration. See the information about registration-based enforcement of the emissions inspection requirements. You must have the vehicle repaired to meet the standards and pass a reinspection.
    Inspection Waiver. A vehicle that is required to have the OBDII inspection can qualify for a waiver if:
    • The vehicle fails the OBDII inspection, but passes the safety inspection, the gas cap check, and the visual inspection of the emission control devices, and
    • The vehicle receives repairs that are related to the failure of the OBDII inspection and the cost of the repairs is at least $450, and
    • The vehicle does not pass the OBDII inspection during a reinspection.
    The waiver is valid for one year.
    After the reinspection, the inspector enters the repair information that you provide into the NYVIP equipment. The NYVIP equipment then notifies the inspector if the vehicle qualifies for a waiver. If the vehicle qualifies, the inspector can use the NYVIP equipment to print a waiver form. You must sign the waiver form, and the inspector must sign the waiver form. The inspection station keeps the waiver form and other documents related to the waiver. The inspector then issues your inspection sticker, and the sticker is valid for one year.
    To qualify for a waiver:
    • You must have the inspection report from the original NYVIP inspection station.
    • The inspection report must show that your vehicle failed the original OBDII test, but that your vehicle passed the safety inspection, the gas cap check, and the visual inspection of the emission control devices.
    • The emissions control system of your vehicle must be intact. The system must not show any evidence of tampering.
    • You must have work orders and receipts that prove that repairs related to the vehicle emissions system were completed at a NYS-licensed repair shop. The work orders and the receipts must prove that the cost of the repairs, parts and labor, was at least $450. If you complete the repairs yourself, the calculation of the cost of the repairs includes only the cost of the parts that were used and does not include any amount for your labor.
     
  3. JimN

    JimN Let the games begin!

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    Once cleared, how long before the code reappears? If I had some time I'd reset the computer just before inspection & hope.
     
  4. tompelletier

    tompelletier New Member

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    The waiver is a possibility, but a literal reading of the terms suggests that the order should be: fail, spend $450, fail again, get a waiver.

    Since I spent more than the $450 in advance, knowing it was going to be a problem, I wonder whether they'll give me the waiver. Also, the waiver is only for a year, so I'll still have to solve the problem eventually.

    I asked the station that failed me about the waiver and they didn't want to do it. "It's too much of a pain," was their reason. I doubt they are allowed to refuse like that, but who knows how long it would take for a complaint to the state to result in any action.

    As for resetting the codes, the problem is that the OBD II system tells you if it hasn't yet gone through its diagnostics. If it hasn't, they won't pass you. In NY, a 2002 is allowed to have one diagnostic not yet completed. I tried several times, but was unable to catch the system at the point between when there was only one diagnostic incomplete and when the check engine light came on. I might have to keep trying that.

    But ultimately, I'd like to find out what is causing this problem.
     
  5. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Hi Tom,

    What is the part number of the engine ECU that you installed? Ideally it should be 89661-47054. If it is 89661-47030, this is the problem.

    When replacing the oxygen sensors, did you use Toyota parts? This is especially critical with regard to oxygen sensor #1 which is upstream from the catalytic converter.

    Have you seen TSB EG017-03? If not, it is relevant to your problem and I attached it below.

    What is the odometer reading on your vehicle?

    It would be interesting if you could verify the voltages coming off the two oxygen sensors to confirm your dealer's finding that the catalytic converter is working properly.
     

    Attached Files:

    BSGPriusOwner likes this.
  6. tompelletier

    tompelletier New Member

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    Patrick,

    Thanks for the suggestions. The ECU I installed is the updated 47054 version.

    >When replacing the oxygen sensors, did you use Toyota parts? This is >especially critical with regard to oxygen sensor #1 which is upstream from >the catalytic converter.

    I didn't use Toyota O2 sensors. But they are not generic ones. They are Bosch ones specifically for this vehicle. The Toyota dealer said they tested fine. Do you know of a situation where non-Toyota O2 sensors caused a problem?

    >Have you seen TSB EG017-03? If not, it is relevant to your problem and I attached it below.

    Thanks. This seems to apply to earlier vehicles, however. Mine is a 2002. But I'll pass it on to the Toyota guys when I bring the car back. Of course, they should know about any TSBs related to their own cars, but my experience has been that that's not always true.

    >What is the odometer reading on your vehicle?

    135,000 miles.

    >It would be interesting if you could verify the voltages coming off the two oxygen sensors to confirm your dealer's finding that the catalytic converter is working properly.

    I don't know what those voltages are. They just told me that it was reading fine.

    Thanks,

    Tom
     
  7. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Hi Tom,

    Note that your profile indicates that your car is a 2001, that is why I thought the TSB might be applicable.

    Another question: what did the catalytic converter rebuild involve? Was the old catalytic converter cut off and a new one welded in place so that the old HCAC chamber and the exhaust tubing was retained? Or was the rebuild less involved than that?

    The reason I asked about the O2 sensors is because the engine ECU is quite sensitive to monitoring the proper voltages. Consider how the ECU determines if the catalytic converter is working or not. It expects the voltage from oxygen sensor #1 to rapidly fluctuate up & down to show that the feedback loop is working and that the Prius air/fuel mixture is oscillating up & down between lean and rich mixture. It expects the voltage from oxygen sensor #2 to stay relatively constant to show that the catalytic converter is "adding value" and not just passing the exhaust gases without processing.

    When I owned my 2001 I had the Ecrostech miniscanner connected to that vehicle. Two of the parameters that I monitored were the O2 sensor voltages. Sensor #1 produced voltages ranging from 0.1V to 0.9V, quickly moving up & down. Sensor #2 produced voltages around 0.5V to 0.7V.

    Since you have the correct engine ECU installed, my guess is that the catalytic converter or oxygen sensor #1 is operating marginally; hence DTC P0420 is being posted.
     
  8. galaxee

    galaxee mostly benevolent

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    did the new cat pipe come with the shutoff valve in the middle of it?
    a code p0420 absent other codes is almost exclusively a cat problem- with the exception of a few ecu issues.

    how long does the code take to recur once it's cleared?

    ummmm... starting to reach here, but any holes in the exhaust?
     
  9. Ecar2001

    Ecar2001 Junior Member

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    My car: 2001 125k miles on it. Code P0420 detected last week. Was told to replace cat. Dealer said that there are different OBDII codes for the 2 O2 sensors. I have read every post in this forum and it seems to me that there are NO CODES for the sensors and that the sensors need to be tested separately. Is this correct?
     
  10. hobbit

    hobbit Senior Member

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    It sounds like those techs have forgotten how to do basic catalyst
    tests by watching waveforms -- it's even all spelled out in the
    service manual. Take the car to another service center if
    you can... or get an independent to work with you on it, partially
    in exchange for their learning about how to deal with Priuses. On
    a Classic, this stuff can be watched by tapping ECU leads and not
    even having to get under the car at first.
    .
    _H*
     
  11. Ecar2001

    Ecar2001 Junior Member

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    Thanks Hobbit. Person who gave me a lecture was NOT the actual technician but the front desk clerk. I will go elsewhere to try to avoid the expense of replacing CAT.
     
  12. bernie3015

    bernie3015 Member

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    Do you have to add oil between oil changes? If so you are burning oil which ruins the Converter. Catalytic Converter clearn and then oil additive to prevent oil burn could solve this.
     
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  13. dolj

    dolj Senior Member

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    Don't know to whom you're addressing your question, but the OP hasn't been on PC for over 9 years and this thread has been dead for nearly 10 years.
     
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  14. Kalicruisin

    Kalicruisin New Member

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    This is very helpful thanks