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    Optimus Member

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    Just got an '02 Prius and it decided to throw some codes today. Originally, a dealership pulled codes when my wife was driving it, and they just told her it was the gas cap. They didn't tell her right away what the codes were, so she called them back and they only said P1436. The light came on again today and I see codes P1436 and P0420. The light came on after the car had been sitting for 4.5 hours and had a chance to cool off. I started the car and the ICE ran for about 30 seconds and the check engine light came on. No other issues seen. Battery charge seems to stay around 60-80% and never goes extreme. Car drives fine.

    Any ideas? I've put 60 miles on this car and do not need expensive failures already.
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    Patrick Wong DIY Enthusiast

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    DTC P0420 Catalyst System Efficiency Below Threshold (Bank 1)
    DTC P1436 Bypass Valve Malfunction

    See pages 2-11 and 2-12 of the following document:
    http://www.autoshop101.com/forms/Hybrid12.pdf

    The HCAC valve is stuck, causing P1436. You may be able to lubricate it with high temp grease to get more life out of it.

    However, P0420 means that the catalytic converter is bad. There is a possibility that oxygen sensor #1 might be bad instead of the catalytic converter. You would have to gain access to the sensor voltage by finding the appropriate pins at the engine ECU, to evaluate whether the sensor is the problem or the catalytic converter has failed.

    Its unfortunate that you have noticed this problem so soon after you bought the car - but now you know what motivated the prior owner to sell it. Hope there aren't more surprises down the line for you.
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    Optimus Member

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    Yes, it's a bit unfortunate (luckily I paid what I feel is a fair price and can absorb some repairs). On the plus side, I spoke with a different dealer today and found out the battery was replaced in 2005 and only has about 50k on it now, so I won't have to worry about that. Isn't the bypass valve part of the CC, or am I thinking of a different valve? Looking at the drawing in the link you provided, it looks like they are one component. Could a faulty HCAC operation also cause the P0420 if things aren't bypassing correctly? Code P1436 would make sense because the car came from an area where road salt is an issue, and it's going to be driven in an area where road salt is still an issue. Now that you mention it, I recall reading a post at some point about someone who had P1436 and they mentioned greasing the valve shaft took care of it and just greased it every so often.

    Looks like the first dealership was wrong.... Even the experts can't get it right. This is why I prefer to work on my own cars.
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    Patrick Wong DIY Enthusiast

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    Yes, the HCAC valve is part of the HCAC, which is upstream of the catalytic converter and is all one physical piece. However failure of that valve would not cause the P0420 code.

    My 2001 had logged all of its miles in Honolulu and southern CA, no salt applied on the roads in those areas. However the HCAC valve made a funny squeak upon first startup. I lubricated the valve using lithium grease and the squeak stopped for a while. However it later returned, and I assume that the grease burnt off since the HCAC gets pretty hot.
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    Optimus Member

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    So worst case scenario, I'm looking at a bad cat (if the valve is not fixable) and a bad 02 sensor. Best case scenario is a bad cat and a bad valve, all one unit. I'm going to look for an exhaust from a salvage car. I sent an E-mail to a place called xviper that someone else on this board mentioned getting something from.

    Does anyone have any other recommendations on sources? I'm not going to pay $1600 for this thing. (despite the fact I will be installing it myself). I already know after market CC's won't work because of the valve built into it, so I'm not going that route.
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    tochatihu Senior Member

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    LKQ online offers many salvaged Prius parts on ebay, and they are big. I am not sure that either of thiose statements represents a strong recommendation though.

    Has anyone reading ever bought from them?
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    gippah New Member

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    My CEL turned on last year with code P0420. Toyota technicians see that as a catalytic converter replacement and don't do much troubleshooting beyond that, if any. Toyota charges $1600 for the part and with their weird labor formula it ends up being $2200. I declined, and the light turned back off after awhile.

    As this was going on, I asked a friend who owns a Toyota dealership and service center in California about this. She said that this is a KNOWN PROBLEM with the early Prius and she was surprised that there has not been a recall for it.

    At $2000 a pop, I think we know why there hasn't been a recall.

    Anyway, with P0420 I would let it go, my light went off after 4-6 weeks and hasn't returned ... unless you really want to spend 2 grand on a car that's not worth much more than that. I would DEFINITELY try the oxygen sensors first ... and remember that there are generic catalytic converters out there that should fit any car for $100 so that would be the reasonable 2nd option. Unfortunately, it is illegal to buy used/salvaged CCs.
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    ChapmanF Senior Member

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    Apparently that is an option, when done carefully enough. Art's Automotive has a nice article on it. $100 might be a tad low.

    -Chap
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    Optimus Member

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    Well, luckily, neither codes have come back since I posted this. I was expecting them to come back shortly thereafter, but they haven't. We've put probably 2000 miles on the car in the meantime. I haven't done anything but clear the code. I suppose it's plausable the code(s) came because the car sat for a month after we bought it but before we actually picked it up. The vacuum canister rod (which I haven't even looked at yet) could have rusted in place a little while sitting, and cleaned itself up after driving it a while. Speculation at best, but either way, no codes for the time being.
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    MaxFrenzy New Member

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    My story is damn close to yours. Picked up our used 2001 Prius on Thursday night and today (Monday) it throws a check engine. I brought it to the dealer and they told me code P1436. It turns out the previous owner had the problem a few months ago and opted not to fix it (I brought it to the dealer that the previous owner had all work done at). They told the previous owner that the bypass actuator assembly would have to be replaced. Is this the $2000ish part that you're speaking of above?
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    MaxFrenzy New Member

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    I wanted to update this thread with information about my situation. The dealer called back today and said that catalytic converter would need replacing but that they would cover it under warranty. They said that part was around $1300 dollars or so. So that part is good. However, they are making me pay for an O2 sensor. I guess it was rusted onto the old assembly and they wouldn't be able to get it off without breaking it or something. I didn't quite understand what the situation was, but that's what I got out of it. So, all in all, this will end up being significantly cheaper than it could have been. For anyone else out there who has this problem, fight for it to get covered under warranty if you're still elgible. I'm on an 01 Prius with 43K miles and only a few months left of coverage.
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    Optimus Member

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    Thanks for the update. My '02 has about 127k on it now, so I'm way passed the warranty. Luckily, my codes still haven't come back after a few thousand miles of driving.

    Oh, and I missed your original post. Yes, we are referring to the same $2000 (roughly) part. The catalytic converter has a small "thing" on it that makes it very unique from standard catalytic converters, and that is the bypass valve. So, both items are one and the same part (or at least not removable from each other) and we are talking about the same thing.

    It is not the least bit uncommon for 02 sensors to be rusted in place, however, 02 sensors are often held in with 2 nuts that are threaded on to studs on the exhaust pipe itself. If the nuts are rusted and rounded off, it can make removal more difficult, and possibly having to put new studs or a new bung on the exhaust pipe. The nuts can usually be broken off and saving the studs, and then the 02 just comes right off. I haven't checked under the car to see how the 02 sensors attaches, but I'm a little surprised they say the 02 will be damaged. Maybe they are basically just saying they could spend enough time trying to save the old 02 sensor to reuse it that you'd be paying ehough labor charges to just buy a new one anyway.
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    Ecar2001 New Member

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    Question relevant to code P0420. Is there a separate code for the O2 sensor(s)? Was told yesterday that with P0420, the cat needed to be replaced. I asked about the sensors but was told that there is a separate OBDII code for the sensor(s). I read everything on this forum and there's no mention of a sensor code as opposed to generic P0420 code.
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    Patrick Wong DIY Enthusiast

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    Yes. DTC P0130, P0133, and P0135 relate to problems with oxygen sensor #1.
    DTC P0136 and P0141 relate to problems with oxygen sensor #2.

    However it is possible that a marginal oxygen sensor #1 may cause DTC P0420 to appear. So if you want to take a chance, you could replace oxygen sensor #1 with the correct new Toyota part (not an aftermarket part) and see if that helps.
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    bedrock8x Senior Member

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    I agree to replace the #1 O2 sensor.

    My girl friend's 03 Corolla keep throwing P0420 code after reset every time. Replacement fixed it.
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    schrojan New Member

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    So what if the only code that is showing is the P1436?
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    Patrick Wong DIY Enthusiast

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    1. Raise up the car, get under it, and see if you can lube the HCAC valve with high temp grease to free up the operation of the valve. The valve will be upstream of the catalytic converter.

    2. If that doesn't work then you can either replace the HCAC chamber and catalytic converter (which will cost into four-digits) or else you can...

    3. Ignore the problem.
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    acelliott New Member

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    Unfortunately in Milwaukee, option 3 is not viable. My wonderful SULEV sticker doesn't carry any weight at the emissions testing facility. Second year in a row that I have had my jack out, my PB Blaster and Carb Cleaner cans in hand, and my crescent wrench under the car, working the valve back and forth until it cleans up and operates freely. Then it is up to my OBDII reader and several days of driving until I can go back to the DMV once the codes are set. I'm afraid to try the lithium grease for the same reason mentioned earlier, that it would carborize and gunk up the valve once it overheats. I have similar fears about the PB Blaster but am hoping that the Carb Cleaner will wash it away. Thoughts? (P1436 is the culprit here BTW with occasional P0420 following)
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    msdickerson Junior Member

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    yes the hcac valve is a valve in the middle of the cat assembly which from toyota, costs about 1600$/2000$ installed. Try lubing the valve, and working it free by hand. It often makes it work fine for a year or two. It is a known issue on these cars, and Toyota supposedly had changed the part over to something better, but I do not think that was true (dealer told me that a few years ago).

    steve d
    02 super white 229000 miles

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