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Brake / ((!)) / ABS / VSC Strikes Again

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Jeff Martin, Jan 2, 2023.

  1. Jeff Martin

    Jeff Martin Junior Member

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    This is a brief saga; hoping it helps someone or maybe responses will teach me more.

    We had this happen twice to us this year - Brake / ((!)) / ABS / VSC lights all on constant and long beep upon starting our 2008 Prius. Looked like this:

    upload_2023-1-1_21-25-57.png

    The first time happened months after hearing a chattering pump sound (increasing in volume and length of time) from the engine compartment when opening the driver's door and starting the car, and later a chirping/barking noise when holding the brake peddle at a full stop. Once the warning lights appeared and stayed on constant, I read codes with my TechStream that told me the accumulator system failed. The brakes never actually felt different than what we were used to at that time, but knowing what was coming (from PriusChat), we of course replaced that part. Did the work myself after lots of research, cleared the codes, and drove for months with fantastic-feeling brakes, no dash warning lights, and no problems.

    The second time, five months later, that same set of lights and the long beep returned and stayed on constant. What a sickening feeling... could that expensive accumulator assembly really have failed so soon?! This time, the brakes immediately felt different... much harder to come to a stop. While diagnosing a few days later, I carefully drove quiet streets and noticed an occasional grinding sound from the driver's-side wheel. Smelled "hot brakes" when I parked.

    Checked codes with TechStream:
    * C1246 - Master Cylinder Pressure Sensor
    * C1256 - Accumulator Low Pressure
    * C1341 - Hydraulic System (FR)
    * C1364 - W/C Pressure Sensor
    * C1365 - ACC Pressure Sensor
    * C1391 - Abnormal Leak of ACC Press

    I pulled both front tires to check the pads; expecting to see no pads, metal-on-metal (hoping desperately this was some designed fail mode of the system causing the dash lights)... but there was plenty of pad left on all four.

    Then I saw something I've never witnessed before - the thin metal plate (anti-squeal plate, I think) delaminated from the steel backing of the pad and rotated outside of the calipers to grind itself into the hub. (Pictures below). This likely caused the wheel to studder a bit upon braking (I think I felt that a couple times)... maybe even triggering an ABS error resulting in the dash lighting up (like above). Maybe?

    upload_2023-1-1_21-35-20.png

    upload_2023-1-1_21-36-30.png

    upload_2023-1-1_21-37-4.png

    upload_2023-1-1_21-38-5.png

    I got a warranty replacement on those pads, replaced them, reset the codes, and to my surprise the braking system returned to normal (excellent response, no dash warnings). It's been two weeks now and hundreds of miles.

    What do you think? Would the ABS/VSC system respond this way, throwing errors and basically disabling the automatic system (very little assist in brakes) if something intermittently obstructed the wheel motion like this? I can't believe it, but I have no other explanation at this point.
     
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  2. Tombukt2

    Tombukt2 Senior Member

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    I I don't see how that could interrupt the braking system enough to set a code but that's quite interesting and the replacement part your accumulator pump was that new 13 $1,400 or just a used part? The only reason I ask is because if it's a used part then of course it can fail at any time just giving his general makeup course if you're lucky in the person who owned the car prior to you getting the part off of it had replaced this part and then wrecked the car hence you see it at LKQ and are taking the part out then maybe you're lucky for a long time this is possible sometimes while you're at the junkyard looking at a car to get parts off of you can look up its history online and see major events that have happened like this brake part being replaced.
     
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  3. ChapmanF

    ChapmanF Senior Member

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    I could potentially see that being responsible for the C1341, if that was on the right side (but it looks like the left??). If something is wiggling the pad around while braking, you can get one of those codes about wheel line pressure not staying on target.

    The connection to any of those other codes seems less convincing.
     
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  4. Jeff Martin

    Jeff Martin Junior Member

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    Right, my thoughts exactly, but then my dad (a truck driver) reminded me that he'd had that same thing happen to him on his rig and it locked up the wheel long enough that the tire blew, so maybe there's something related here. Still hard for me to believe though.

    Yes, brand new, $1,200 part direct from Toyota. Had to call around the country to find one since there was a supply chain issue and most dealers were way back ordered. I wasn't going to mess around with any used parts; critical system on a Gen 2- any of the best used parts would be old and likely well-used too.
     
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  5. Jeff Martin

    Jeff Martin Junior Member

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    Thanks for your thoughts; reflects my own too. I'm still leery of fully trusting it... but now we've been through even a serious rain/wind storm for a few days with no degradation in performance. Also, thanks for bringing up the C1341... does that (FR) mean "Front Right?" That's what I'd figured, but there were no visible issues on the front passenger's side.

    Also, I didn't mention it, but I pulled both speed sensors (ABS sensors?) on the front to check them for debris. Both were cleaner than I expected. I wiped them and did not see anything unusual in their access ports.
     
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  6. Tombukt2

    Tombukt2 Senior Member

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    I paid $200 used and I've been driving on that used part for 6 months now maybe a little better No problem I'm picky about where I get the used parts from so this one may have just been replaced in the last year or so by the previous owner of this mint condition car that had a light hit in the back and got totaled by the insurance company I quickly retrieved all the parts from it It looked like it had been very well maintained so that's a possibility I didn't Google the VIN number or do any searches to see if the car had been in for anything like that didn't really matter I needed to do this regardless I wasn't going to pay $1,000 for a break part If anything I would get that from the JDM importers from a low mileage takeout car from the country the car came from but some people you know they just have to have the best possible outcome they can so going new is generally the way to go but as we see with electronic parts they can just fail at any time because they're just that electronic hopefully this is further down the line and something else is causing the problem with your suss out pretty quickly Good luck.
     
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  7. Tombukt2

    Tombukt2 Senior Member

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    I guess I'd be pulling that shim and that caliper off that side off and maybe replacing the pad set at least on that wheel and if I'm doing it on that one I'm doing it on the other side too just because and so I have proper shims attached to the pads correctly etc and go from there how that slipped down and all that don't know don't worry must be not connected to the pad properly or something something got loose for a reason heated up whatever was able to slip down so fix that and see if that cures the problem obviously with a accumulator pump assembly that's brand new and not that old I wouldn't generally be looking at that right away after seeing these other things
     
  8. mr_guy_mann

    mr_guy_mann Senior Member

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    I would think that the pad shim is unrelated to whatever codes you had.

    Any chance a connector on the actuator or brake ecu isn't fully seated?

    What does your boost pump do right now? Does it stay off if you don't use the brakes while in ready mode?

    I can't come with any single fault that would cause all those codes to set.

    Posted via the PriusChat mobile app.
     
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  9. Jeff Martin

    Jeff Martin Junior Member

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    It's been a few weeks and apx. 1,000 miles of normal city+highway since my last update; still no problems.

    re: connector - Not likely; I should have had another incident from vibration by now, and I'm confident I made sure all the connectors clicked into place while I reinstalled everything.

    re: boost pump - After car sitting for hours, touching the handle (to unlock) and opening the door... totally silent. (This was definitely NOT the case when our old accumulator system was failing; the boost pump would start running as soon as we unlocked the door and would continue for 1 min or so). With car off, pressing on brake the brake activated the boost pump for about 4 seconds, then stopped silent. Turned car on to Ready mode; still silent. Release brake and wait, still silent. This is exactly as it should be with a properly-working brake accumulator system.