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Monitoring brake accumulator pressure

Discussion in 'Prius v Technical Discussion' started by Designated_david, Apr 23, 2022.

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  1. Designated_david

    Designated_david Junior Member

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    Good day all,

    I have a 2014 Prius V Two. I know the brake stroke simulator/accumulator has been a thing in Gen 3, and the best I can figure is that by 2014 the internal leakage issue has been solved by Toyota, and I'm pretty sure the car I have isn't afflicted with this problem.

    That is not to say that the car isn't subject to a similar failure. As of right now, I have no problems with the car, however, I am noticing that the accumulator pump is running just a tad more often than it used to when I bought the car. And to be fair, the town I'm in is a harsh environment with regard to traffic, selfish drivers, and I find myself braking aggressively far more than I care to.

    So I'm not having any immediate problems, but I did recently see a YouTube video of a guy working on a Gen 3 using a bi-directional scan tool (properly) to bleed down and replace the brake stroke simulator with one provided by his customer. WHAT INTERESTS ME is the PID that he was monitoring and that is accumulator pressure. Without spending a fortune on a scan tool, I do have a bluetooth OBD dongle and Torque Pro with the PRIUS PID package installed, and this PID is not among them. Is there a way to monitor accumulator pressure to see if the pressure is dropping while holding the brake pedal? I want to be sure the pressure is holding properly.

    In similar fashion (and unrelated) I was able to input a custom PID forumla for my trans fluid temperatures on my Tacoma so I can do a proper fluid check without the Illuminati secret hand shake. So is this possible for the Prius?

    Again, I don't have an immediate concern, just want to keep an eye on things.

    Thanks, and have a great day!
     
    #1 Designated_david, Apr 23, 2022
  2. rjparker

    rjparker Tu Humilde Sirviente

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    Actually there is a good chance you could have the issue at some point. Hopefully you are well under 150,000 miles so you might qualify for repair when it codes.

    31BD0CAD-098B-4A94-840C-2B8F84703A26.jpeg 880EAAD1-F6AA-476B-9517-D783B0BE5AFD.jpeg
     
    #2 rjparker, Apr 23, 2022
  3. ChapmanF

    ChapmanF Senior Member

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    There clearly is such a PID if Techstream can display it, but possibly no one has reverse-engineered its address and decoding yet, to add it to an available "PID package" like Torque's. It is generally up to some enthusiasts to do that work, and my hat is off to those who worked out so many of the earliest-generation Prius PIDs (like vincent1449p, thank you!).

    Maybe you could be the first!

    It would be worth searching the forums here; at one time there were documents (often Excel spreadsheets) containing all the so-far reverse-engineered PID details for some of the Prius generations. I'm guessing those will be where Torque's "PID package" originated, so I don't know how likely it is that the accumulator pressure was in there but didn't get copied to the Torque package. But it would be easy enough to check and you might get lucky.
     
    #3 ChapmanF, Apr 23, 2022
  4. mr_guy_mann

    mr_guy_mann Senior Member

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    You could look at a couple different apps to see if they had the data you are looking for. I reviewed several apps for the Gen2. Might want to try CarScanner (this app seems to only see ecu's that are completely on CAN bus. It didn't have ABS for Gen2 - but Gen3 might as it handles more diagnostics over CAN vs Gen2 ). The free version should let you scan a the car for whatever ecu's that the app can handle.

    Another option would be OBDFusion. $15 gets you access to a single model year of Toyota. On a Gen2 with a cheap (BAFX) adapter- it had codes and data for the "major" systems - including ABS. (I specifically looked for and found accumulator pressure sensor voltage on my 06). Again I might expect coverage for a Gen3 to be broader as more systems are on CAN bus.

    If you find either app has ABS data, you will want to monitor accumulator pressure when you are NOT using the brakes. One of the big failure modes on a Gen3 appears to be internal leakage that allows high pressure fluid to bleed off. This causes the pump to cycle (often) to keep the system charged- even when there is no use that would discharge the accumulator.

    The second failure mode is leakage of the "precharge" in the accumulator. This reduces the "storage capacity" of the accumulator, causing the pump to run more often- but only when the brakes are being used.

    Posted via the PriusChat mobile app.
     
    #4 mr_guy_mann, Apr 28, 2022
    Last edited: Apr 28, 2022
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