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How long does the car store codes?

Discussion in 'Generation 1 Prius Discussion' started by jdms2000, Nov 27, 2009.

  1. jdms2000

    jdms2000 New Member

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    Vehicle:
    2002 Prius
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    Does anyone know how long a 2002 will store check engine light codes? My CEL turned on last week. One dealer read the code and said it was a bad catalytic converter. The CEL's now off, but I want to go to another dealer to have the code read. Just want to ensure that the code's still there.

    Thanks.
     
    #1 jdms2000, Nov 27, 2009
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  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    It's hard to say. Since you probably have to pay for an hour of diagnostic time each time you ask a dealer tech to read the codes, I suggest you wait for the check engine light to reappear.

    Regarding the Classic catalytic converter, one failure is due to sticking of the HCAC valve. This failure can be temporarily fixed by applying high temp lube to the valve mechanism. It is a temporary fix as the lube will eventually burn off.

    Another failure is due to the catalytic converter losing efficient operation as it ages. If you replace oxygen sensor #1 instead (a much less costly repair), that might be sufficient for the engine ECU to think that the converter is "good enough".

    The reason for this is that as the oxygen sensor ages, it takes more time to respond to changes in the air/fuel ratio. The engine ECU expects to see a rapidly fluctuating voltage from oxy sensor #1 and a relatively flat voltage from oxy sensor #2. Therefore a new oxy sensor #1 might produce better results for the ECU.
     
    #2 Patrick Wong, Nov 27, 2009
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  3. jdms2000

    jdms2000 New Member

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    Vehicle:
    2002 Prius
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    a few dealers offered to read the code for free. i want to test again because before having dealer 1 pull the code, i said that it was probably a bad cat...of course, that's what the dealer ended up saying the CEL was about. My CEL recently turned off and my MPG has been the same. I'm wondering if the CEL was really about the cat or something else that's much cheaper to repair.

    i'll lube the hcac valve, though.

    if o2 sensor 1 was going, would i get a code for the sensor versus the cat?
     
    #3 jdms2000, Nov 27, 2009
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  4. Patrick Wong

    Patrick Wong DIY Enthusiast

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    I believe that the sensor has its own DTC. However when the sensor and the catalytic converter are both marginal, how does the engine ECU decide which code to log?

    Anyway, some owners have managed to avoid the bullet of paying $2K for a new catalytic converter (at least temporarily) by replacing the oxygen sensor. Your results may vary...
     
    #4 Patrick Wong, Nov 27, 2009
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  5. nerfer

    nerfer A young senior member

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    It looks like it's stored pretty much forever (until you disconnect the battery or clear it with a diagnostic tool). Go to the bottom of page 2 here: http://www.autoshop101.com/forms/h46.pdf (This is OBD-I, but the follow-up description of OBD-II doesn't seem to negate it).

    Automotive Training and Resource Site has information specific to Toyota in the Technical Articles section.

    Multiple codes can be logged at a time. There are tools available to the consumer for reading & clearing the codes, along with reading engine data. If there's a Prius group meeting in your area, somebody might have a ScanGauge or similar item available.
     
    #5 nerfer, Nov 27, 2009
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