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ABS system problems (C1256, C1391) - can the car drive safely?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Vae70, Oct 1, 2020.

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  1. Vae70

    Vae70 New Member

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    Hi folks,

    I recently found some issues with my 08 Prius where the ABS, VSC and (!) lights came on. I took the car to a reputable hybrid shop and they diagnosed "an internal issue with the ABS unit" showing error code C1256 and C1391. When asked about the safety repercussions of the ABS failure, the shop manager told me that the car would drive fine under normal conditions and that the failing ABS module would only cause issues if I were to enter conditions that would normally cause the slip detector to trigger (rain, snow, etc) and that I'd be fine otherwise on the city and the highway.

    I figure the lights are finally coming on after a couple of months of me noticing a weird "consistent rattling noise" coming from the engine when I drive. Some quick googling today has me thinking this noise has been the ABS pump running constantly.

    I have driven the car twice since the lights came on, about a half hour to the shop and back. Both times paying close attention to the breaks, nothing seemed to be different from how the car usually drives.

    I'd like to fact check what I was told as to my knowledge, any kind of ABS issue should impact the normal function of brakes even between 20-60mph (my typical speed range)....... but this isn't. It should be very unsafe to drive the car....... but it doesn't seem to be so and the mechanic says its safe, I'm very confused given the conflicting info I was given - would appreciate some help
     
    #1 Vae70, Oct 1, 2020
  2. rjparker

    rjparker Tu Humilde Sirviente

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    If it was just abs as the shop said AND it was a conventional car that was not brake by wire with regen THEN the shop is essentially right. ABS is antilock braking which does not get used in normal braking. The Prius has ABS but thats kids stuff compared to what it does with its computer controlled master cylinder that has its own hydraulic pressure pump/accumulator.

    If that pump is leaking it takes too long to build pressure. That is what you likely heard. Both codes are about the pump and accumulator, not the abs. It is one big assembly with a pump, accumulator, abs, master cylinder and brake ecu. If the pump runs too long it sets those codes as a warning. The system has a failsafe should the pump quit but the brakes will get much harder to operate and normal stopping distances can get long. Long enough to cause a crash that normally would have been easy to avoid.
     
    #2 rjparker, Oct 2, 2020
    Last edited: Oct 2, 2020
  3. Vae70

    Vae70 New Member

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    Thanks rj, I assumed what you were telling me is the case. Is there a way to tell how much "life" is left on the pump? The whirring i've been hearing has been going on for months without much of an issue. In either case its probably time to hunt for a new car but wondering if its even safe to take it to the shop or to get some detail work done before sale.
     
    #3 Vae70, Oct 2, 2020
  4. rjparker

    rjparker Tu Humilde Sirviente

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    Its a big unknown how long it would be "safe". I certainly would be cautious with it and consider the possibility of increased stopping distances. Personally I would take it to the dealer and ask for their opinion.

    Realize that a car with this kind of recurring fault is not going to be worth much to a private party and maybe a token $500 as a trade. The running joke is the rare metals in the cat are worth more than the car in some cases.

    If the car is relatively low miles and clean, a repair and a private party sale might be justified to net a few thousand while delaying a new purchase (although now is probably a good time to buy).
     
    #4 rjparker, Oct 2, 2020
  5. Vae70

    Vae70 New Member

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    I agree with you here, if the car was in good condition it would be! The problem is everything else - 147k miles, dead combo meter and a hybrid battery due for replacement soon (dealer says 2yrs or 10-12k miles). I'll certainly take it to the dealer to see what they say it cant hurt.

    Ideally, i'd love to drive the car longer but given the compounding repairs (meter and pump short term, battery long term) it seems like getting a $500 trade in credit may be best
     
    #5 Vae70, Oct 2, 2020
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