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Replace Brake Accumulator Pump?

Discussion in 'Gen II Prius Main Forum' started by Marvinh, Mar 21, 2009.

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  1. Marvinh

    Marvinh Marvin

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    I have a ratchety / pump noise when I start from a cold start and sometime when I switch from 'Park' to 'Drive'. But NOT when I just pump the brake pedal.

    The dealer diagnosed it correctly as the brake accumulator pump. There is a technical service bulletin that says to try bleeding the brakes first. And if this doesn't work, replace the accumulator pump. The TSB also says there is no impact on brake performance. Well, the bleed didn't help so now the dealer says to replace the accumulator pump.

    However, its a big job. It involves taking the inverter off and other connectors to get at the pump. About a 4 hour job. Has anyone had this done (under warranty by the way)?

    I am concerned about doing an involved job just to correct a noise that the TSB says does not affect brake performance. But I am concerned that the pump may fail in later years.

    Can I have your thoughts on this? Thanks! Marvinh
  2. galaxee

    galaxee mostly benevolent

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  3. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Hi Marvin,

    Since you can get this work done under warranty, it makes sense to do so. That pump replacement would be quite expensive if unwarranted.

    I suppose you are concerned that the tech might screw up the job? I think that the likelihood of that happening is relatively low, and you'll immediately know if there's a problem.

    You'll have to weigh that possibility vs. the possibility that the brake pump might fail after the warranty expires. Good luck with your decision.
  4. Marvinh

    Marvinh Marvin

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    Yes, I am concerned that this is a major job and there could be a srewup.

    The Technical Service Bulletin I saw said this does NOT affect brake performance, so I'm wondering if anyone else has heard this noise. It is NOT the same noise as the coolant pump transferring coolant back to the engine on startup.

    I'm thinking that if its just a normal hydraulic pump noise its best to leave it alone.

    What do you guys think? Marvinh
  5. richard schumacher

    richard schumacher shortbus driver

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    Have it done under warranty. Then the dealer has to make it right, regardless, and no cost to you. I suspect that if you don't have it done it'll bother you forever, and this is not a job for an amateur.
  6. judymcfarland

    judymcfarland Queen of Moral Indignation

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    I'm guessing this is the "toot" or "seal bark" noise that I occasionally hear when I have my foot on the brake but the car is not moving. I haven't been able to convince the dealer that I have this noise, but it is on the record that I have reported it.
  7. Marvinh

    Marvinh Marvin

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    Judy - the seal bark noise is the brake actuator pump. That's different from the brake accumulator pump. Marvinh
  8. geeky teacher

    geeky teacher New Member

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    For what it's worth, I had the brake actuator assembly replaced under warranty. I did not want to drive a one year old car that sounded like loud squeaky mattress springs scraping metal on metal when the brakes were fully depressed. It's been a year since without problems.
  9. danl

    danl New Member

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    Hi I hear this noise too in the same situations. Is it a problem?
  10. richard schumacher

    richard schumacher shortbus driver

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    If it's continuous and unchanging for its duration, and is not different in warm weather, then probably not a problem.
  11. Marvinh

    Marvinh Marvin

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    That is a little different than what I and Danl are hearing. The brake actuator pump will make a noise every time the brake pedal is pressed. The brake accumulator will make a noise when it needs to build up brake pressure in the system.

    Marvinh
  12. galaxee

    galaxee mostly benevolent

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    the actuator and accumulator are not separate. the only pump in the actuator is the accumulator pump. the actuator itself only makes noise when it runs the accumulator pump.
  13. danl

    danl New Member

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    How often do you hear this noise? How often SHOULD you hear this noise? On my drive to and from work, I'd hear it between 5-15 min intervals. Possibly more if I brake more often. Is that normal? Is it actually a hydraulic pump storing brake fluid? I though it was some electrical system of a bunch of capacitors.
  14. Mike Dimmick

    Mike Dimmick Active Member

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    I don't recall hearing it when I haven't used the brakes, but my commute is only 30 minutes (at best) and 15 of that is in residential streets where braking is more common.

    Yes, it is a hydraulic pump. See this brake system schematic:

    [​IMG]

    This is the hydraulic system - double lines indicate brake pipes. In normal use SMC 1 and SMC 2 are closed, preventing flow from the master cylinder to the front pistons. Pressing the pedal increases the pressure sensed by PMC 1 and PMC 2. The fluid flows into the Stroke Simulator, which provides the pedal feel.

    PMC 1 and PMC 2 feed electrically into the Skid Control ECU, which decides how much braking is required. It asks the Hybrid Vehicle ECU (HV ECU) how much braking force it can provide with regen, and uses the friction brakes to make up the difference, and also any special braking to keep the vehicle stable. The pressure in the actual brake lines comes from the accumulator - basically a reservoir of high-pressure fluid. The pump runs whenever the accumulator pressure (measured by PACC) is lower than a programmed value.

    To apply the brake to a given wheel, the appropriate SLA solenoid is opened, which increases the pressure in that brake pipe - it's closed again when the appropriate pressure is reached (measured by PFL, PRR, PFR, PRL). To release the brake, the SLR solenoid is opened, which returns the fluid to the reservoir. By opening and closing these valves, it can modulate the braking force.

    It's my belief that any car labelled with 'Electronic Brakeforce Distribution' has such a 'dual-circuit' braking system. The only wrinkle in the Prius is the interaction with the HV ECU for regen.

    The box of capacitors, next to the 12V lead-acid aux battery in the rear, is a back-up power supply to allow some assist braking, should the 12V supply fail utterly and the Skid Control ECU no longer be able to perform its task. The fail-safe mode - where all valves close except SMC 1, SMC 2, which open - has no assist and can only brake the front wheels.
  15. JayGoldstein

    JayGoldstein Member

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    I reported to my dealer that my Prius very intermittently makes the noise described in the Toyota USA brake actuator TSB (BTW, the Canadian TSB is #2725). Although the noise didn't occur when the technician checked the car, the service manager authorized replacing the actuator assembly under warranty.

    Interestingly, the technician said that it would be a waste of time first to bleed the brake system to see if that got rid of the noise. Replacing the actuator assembly was the was the way to proceed.

    I'll be bringing the car in soon to have the work done.
  16. JayGoldstein

    JayGoldstein Member

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    I had the work done yesterday under warranty. I dropped off the car at 8:45 a.m. and it was ready to go at 5:30 p.m. When I got the car back, I noticed that both trip odometers and the odometer on the fuel consumption screen of the MFD were reset to 0, and all my radio presets had been lost. No big deal.

    With the new actuator, putting the car in Ready mode is pleasantly quiet. I had complained about a "squawk" that occurred intermittently when releasing the brake after putting the car in Ready mode. I now realize that I had gotten used to hearing the softer noises that the defective actuator had been making for some time.

    I'm a happy camper.
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