Tricking HCAC codes into going away?

Discussion in 'Generation 1 Prius Discussion' started by aiden, Jun 9, 2021.

  1. aiden

    aiden New Member

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    Hi there,

    The catalytic converter incl. the HCAC system was stolen from my 2002 Gen. 1 Prius. Installing an aftermarket cat would still cause a DTC for the HCAC valve not being able to close (P1437). I'd like to avoid having to replace the entire front exhaust assembly, so is there a way I can trick the ECU into thinking the HCAC valve is still working? I've read several posts on here about DTCs P1436 and P1437 for the HCAC valve being stuck closed or open, respectively, but the only solution I have come across seems to be from 2014 posted by user "sly caulfey". In his post he claims:

    I was wondering if anyone has tried this before or could vouch for this working? I'm thinking of trying to clamp the vacuum hose leading to the HCAC actuator shut, and seeing if that has any effect.
     
  2. aiden

    aiden New Member

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    Hey guys,

    If anyone finds this useful, I ended up disconnecting the original vacuum hose leading to the cat, and plugging the plastic T-connector it was attached to with a piece of duct tape. It's a more simple version of the fix I mentioned in my previous post. This did get rid of the P1437 code that my Prius was showing, which was triggered because the vacuum line was previously unplugged, making the Prius think the HCAC valve was stuck open. Unsurprisingly the P1437 code was replaced by a P1436 code, meaning the Prius now thought the HCAC valve was stuck closed since the vacuum line was sealed. Luckily even with the new code, the CEL went away, so I think I might be able to pass emissions after installing an aftermarket cat, which should deal with the P0420 code I was previously getting. When I emissions tested the Prius in AZ, the only code listed as a reason for failure was the P0420 code, so my theory is the HCAC codes should not affect emissions testing if they don't turn on the CEL. The duct tape is only a temporary fix and I plan on plugging the catalytic converter end of the vacuum hose that is dangling beneath my car with something more permanent. I'll keep you guys updated on if this aftermarket cat fix works and try to post pics as well.

    Aiden
     
    #2 aiden, Jun 9, 2021
    Last edited: Jun 9, 2021
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  3. Soren Lorensen

    Soren Lorensen New Member

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    Any update on the HCAC and the CEL?

    BTW, Did you use one of the "Direct fit" aftermarket cats for gen 1 with one cat? I am wondering how well the direct fit gen 2 with 2 cats fit. I mean, I expect some welding is going to be needed, but the thieves took the HCAC assembly and the resonator, so I might as well replace both cats.
     
  4. nimblemotors

    nimblemotors Re Member

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    I just installed the gen2 cat in my gen1. Of course I had to fabricate all the back tubing as you get just the front two cats.
    I'm going to tackle the HCAC codes..
     
  5. Soren Lorensen

    Soren Lorensen New Member

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    Awesome. Keep us posted about HCAC.
     
  6. nimblemotors

    nimblemotors Re Member

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    Well so far I can't get the code to show up on this car. I know my blue one, it showed up right away. It opens the valve when cold, and then closes it when its warmed up, I think the code showed when it warmed up. So it is not so easy to make it notice it isn't working, and so far, I have not gotten the code on the green one.

    btw, to pass smog, you can just warm up the car, clear all the codes, then drive it around until its 'ready', then have it smogged, it will not throw the code until it cold again.
     
  7. nimblemotors

    nimblemotors Re Member

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    So I got the P1436 with the hose plugged up. I had removed the vacuum canister from the exhaust, and plugged it into the hose,
    and the P1436 cleared. As one might expect, the sensor is only measuring the air flow in/out of the canister and not doing checking anything with the actual exhaust. So if one attaches a vacuum cannister to the hose, it should not trigger the code.
    Coming up with one now..you can buy just the cannister from Toyota for $200. I think $2 max $20 is more appropriate.
    I turbocharger waste gate control looks about the same, I have some of those around here.
    Or something else more common, thinking of a syringe in a big size or a epoxy dispensor that already has a spring in it..
     
  8. nimblemotors

    nimblemotors Re Member

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    Finally got it. Took about 4 tries..but the final solution that worked used a pop-up sprinkler and a balloon.

    Hose connected via a drip irrigation fitting on the threaded side of the sprinkler. Gutted the sprinkler inside,
    and kept just the spring and the spring seat, and then covered the top with a balloon (cut off necked down part),
    and secured with a zip tie. When the car turns on the valve, it sucks down the ballon and compresses the spring,
    and then when it off it returns. Over time the balloon might tear, so might need a heavier duty one than a party balloon. I bought some 'water balloons' in the past but could not find them, they are heavy duty balloons.

    So now just tuck the contraption under the hood.
     

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  9. Soren Lorensen

    Soren Lorensen New Member

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    Good Work. I am guessing that attaching pretty much any vacuum actuator to the vac hose would do the trick.
     
  10. nimblemotors

    nimblemotors Re Member

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    What I learned was it has to have a volume that is similiar to the oem unit.
     
  11. ChapmanF

    ChapmanF Senior Member

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    Now that's some inventiveness right there. :D
     
  12. sandy11246

    sandy11246 Member

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  13. sandy11246

    sandy11246 Member

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    Has anyone tried a vacuum advance unit from an older vehicle distributor. It works off manifold vacuum and has adjustable spring tension.
     
  14. Soren Lorensen

    Soren Lorensen New Member

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    Makes sense. I got the cheapest actuator I could find off ebay, which was a used CC actuator from a Honda Goldwing. We'll see if that works.
     
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