How often does the brake booster pump cycle?

Discussion in 'Prius v Main Forum' started by Ronald Doles, Feb 9, 2020.

  1. Ronald Doles

    Ronald Doles Active Member

    Joined:
    Apr 21, 2019
    206
    202
    0
    Location:
    Columbus, OH
    Vehicle:
    2015 Prius v wagon
    Model:
    Two
    I noticed the thread about the brake class action suit and was curious about a different issue with the brake operation.

    My old 97 Odyssey would run the ABS pump to pressurize the reservoir when I first started the car. As that car got older it would occasionally run to repressurize the reservoir while driving. The Odyssey pump was louder but I hear what I assume is the brake booster pump on my 2015 V. I hear it run on every startup and sometimes when I come to a stop with the ICE off I hear it cycling.

    After 20 years, the Odyssey got to the point where it would sometime fail the startup pressure check and I would get an ABS light and code. The ABS was an option that year so we just ignored the light and drove the car.

    Since there is a lot more going on within this braking system, I was wondering if what I am hearing is normal or am I heading for the same kind of leakdown failure that I eventually got with the Odyssey. I suspect that I won't be able to just ignore this code and drive this car.

    Have others experienced this "leakdown then repressurization" cycle while driving?
     
  2. rjparker

    rjparker Senior Member

    Joined:
    Jun 6, 2008
    2,210
    940
    1
    Location:
    Texas Hill Country
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
    Generally cycling when the car door is opened and at least once while braking is normal. Failing usually means pump operations frequently. Mine was every 15 seconds. While driving you can't really hear it in the cabin. Many hundreds of cars per Prius mechanic have seen the Brake Pump Accumulator fail and usually the Master Cylinder/ABS/Traction Control/Regen/Brake ECU (all one component) replaced as well. $2250 at my dealer.

    As it stands now, only the 2010 Gen3 Prius and the 2012-2017 Prius v's are gen3s not covered by the existing special extended warranty by Toyota. This is an extended warranty with extended time unlimited miles. The 2010's time warranty expired in Dec 2019. The Prius v system is a different part number (maybe because of its unique Pitch and Bounce control for a better ride), and has never been covered, even though they fail as well.

    It is important to realize the Prius brakes are essentially brake by wire almost 100% of the time. Regen during deceleration or downhill is the only braking at speed if the pedal is not aggressively pressed. Even at lower than 7 mph or when aggressively braked, the system depends on the brake booster pump and hydraulic accumulator to provide the hydraulic pressure. The car has a device that simulates brake feel on the pedal. All this to ensure high fuel economy by using regen as much as possible. The brake pads often last over 200k because they are not used much.

    By the way, if it fails 100% there are no power brakes at all and you are hoping two normally open solenoids in the master cylinder // component does fail open as designed allowing mechanical brake hydraulics to have a chance to work. It is reported wrecks occur as drivers expect the good braking and regen to work and it does not. Sometimes because the failsafe does not work or sometimes because they don't apply unusually high brake force to the pedal. So they run into someone or something.
     
    #2 rjparker, Feb 9, 2020
    Last edited: Feb 9, 2020
    varun singh and Tim Jones like this.
  3. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    10,120
    7,454
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    In answer to the "how often does it cycle" question, the answer is "depends on a lot of things." From a longer post elsewhere:

    As rjparker said, it's not super easy to hear in the cabin while driving, depending on the amount of surrounding noise. Then sometimes you can. So it's even easy to get sort of obsessive about it just because of a change in how often you have noticed it running, which then makes you listen harder, and you notice it even more.

    Sometimes a part will wear out and need to be replaced, and when/if that happens, you'll be getting codes and alarms or really, obviously frequent continual running of the pump. If that isn't happening, I would try not to get worked up about it.
     
  4. Ronald Doles

    Ronald Doles Active Member

    Joined:
    Apr 21, 2019
    206
    202
    0
    Location:
    Columbus, OH
    Vehicle:
    2015 Prius v wagon
    Model:
    Two
    I hear it once the car is warmed up and when the engine shuts down before I come to a stop. On my old Odyssey, the ABS pump only ran once at startup for the first 20 years that we owned it. After that, it would run every 15 minutes or so which I suspected was an internal leak.

    Thanks for the feedback. You two seem to be among the longest standing members of this website and are really knowledgeable. I appreciate your input.

    Being a techie helped me be proactive about problems but at times I may cross the line from being proactive to paranoid. Reading many of the posts about problems that people are having probably contributes to that. I think that I understand most of the differences between a hybrid and an non-hybrid vehicle now and why and when things are happening. A new sound or behavior causes me to be a little suspicious of this car. It's behavior is so different from any vehicle that I have ever owned.

    My wife is a people person and not the least bit technical. If she picks up a tool, nothing good can happen. She is oblivious to any warning lights or indicators. I think that her biggest thrill is seeing how many miles she can drive one of our cars with the low fuel light on. She just gets in a car and drives it. I will try to be a little more like her.
     
  5. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    10,120
    7,454
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    You really can't count on that. The accumulator that gets pumped up to hold the pressurized fluid isn't all that big, about the size of your fist. The fluid can't even fill that much volume; there's the nitrogen pressure charge occupying part of it. If you watch your reservoir level from fully zeroed down while the pump runs first thing, it only makes maybe a cm difference in the level.

    Every time you apply the brakes some fluid is used. It comes out of the accumulator, goes out toward the brake cylinders. When you release the brakes, the pistons retract and the fluid returns to the unpressurized reservoir. The harder you brake, the more fluid gets shoved out to the cylinders (really! under braking-level forces, metal calipers are elastic and stretch, you can see it with a dial indicator and it ain't even subtle), and returned to the reservoir when you release. Any slight wobble in the rotors will increase the amount of fluid used with every brake application (it tends to push the pistons further back when released, so more fluid returns to reservoir, and more is needed out of the accumulator for the next application).

    The pump runs every time the pressure in the accumulator drops below a setpoint, and pumps it back up again. It'll typically be "every so many" uses of the brake, where "so many" is a smallish number, but depends on a lot. It probably runs more than you notice when you're not paying attention to it.

    It certainly isn't going to run once at the start of your drive and be done, unless you have cut a hole in the floor pan and you're stopping with your feet.
     
    varun singh and Mendel Leisk like this.
  6. rjparker

    rjparker Senior Member

    Joined:
    Jun 6, 2008
    2,210
    940
    1
    Location:
    Texas Hill Country
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
    As I suggested, the Brake Pump/Accumulator will initially run when you open the drivers door and most likely each time you press the brake. I recently had my brake accumulator and master cylinder replaced and can verify the before and after. My system was cycling continuously, taking about 10 seconds to satisfy then pausing 15 seconds before running again.

    The nitrogen charge in the accumulator is separated from the brake fluid by a diaphragm of sorts (a metal pleated bellows). Just like a well storage tank, the compressed nitrogen provides immediate hydraulic pressure when you need it. The prime failure is the accumulator "diaphragm" leaking between the nitrogen and hydraulic fluid.

    There is a pump runtime timer before the abs and brake alarms come on. One reference said five minutes. Meanwhile a new brake pump accumulator may take five seconds to repressurize the system. That nitrogen is also introduced into the brake/hydraulic fluid which also forces the pump to run longer as it has to pressurize the entrapped nitrogen as well. It is possible to get a day or two of close to normal pump operation by bleeding the brakes completely, ideally following the Toyota Techstream brake flushing logic which will open certain pathways at certain times. I proved that on my car before replacing the pump accumulator and master cylinder/ecu.

    If your wife is not aware of the potential for much harder brakes with longer stop times this could be a dangerous situation for her, her passengers and strangers on the road she may meet. I would treat it seriously.
    0D844F18-024D-4EAD-A9D2-5242B3AA5094.jpeg
     
    #6 rjparker, Feb 10, 2020
    Last edited: Feb 10, 2020
    Tim Jones likes this.
  7. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    10,120
    7,454
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    There is another failure mode that can also lead to excessive pump cycling and has nothing to do with the accumulator bellows. If there is any small internal leak in the hydraulic system, say an incompletely seating valve, that allows the pressurized fluid to slowly escape the accumulator and return to the reservoir, then that will also lead to more pump cycling, even though the nitrogen is staying right where it belongs. Most of the valves that could be culprits in that scenario are in the actuator assembly rather than the accumulator assembly (but not all of them).

    I don't know that we have enough information to say which failure is more common, or the "prime" one. For the record, the trouble codes indicating "small internal leak" refer to the hydraulic kind. There was a recall about accumulators with bellows prone to leaking nitrogen, but that applied to a run of accumulators where the metal bellows were made slightly undersize, so they bounced around inside the can while driving, and developed cracks. Those accumulators could be recognized by the orientation of the label.

    In my experience, it's not usually each time the brakes are used, but every smallish number of times. Harder braking will deplete the pressure faster, as will longer brake travel (related to disc runout, for example).
     
    Tim Jones likes this.
  8. rjparker

    rjparker Senior Member

    Joined:
    Jun 6, 2008
    2,210
    940
    1
    Location:
    Texas Hill Country
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
    Agreed. After the 2010 "recall" Toyota started replacing both the accumulator and master cylinder. In my case we did both as well although a flush of the system would "solve" the problem for a day or more indicating a hydraulic leak was not the likely cause. In a sense the real issue is Toyota has left off the Prius v when even the dealers tell me plenty have failed.
     
  9. Tim Jones

    Tim Jones Active Member

    Joined:
    Jul 17, 2018
    779
    307
    3
    Location:
    SE Texas
    Vehicle:
    2013 Prius v wagon
    Model:
    LE AWD-e
    I'm rite in the middle of all of this.......... one thing I have noticed is that when moving very slow and my foot on the brake I can feel magnetic pulses in the entire vehicle.... feels like a PMA pulse but could be the antilock.
    Pump runs excessively.
     
  10. rjparker

    rjparker Senior Member

    Joined:
    Jun 6, 2008
    2,210
    940
    1
    Location:
    Texas Hill Country
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
    It is the pump operating changing the pressure. Feels something like warped rotors. You won’t feel it when its holding pressure better.
     
  11. Tim Jones

    Tim Jones Active Member

    Joined:
    Jul 17, 2018
    779
    307
    3
    Location:
    SE Texas
    Vehicle:
    2013 Prius v wagon
    Model:
    LE AWD-e
    I need to get this changed out....... Going to need the car for a couple of road trips......
    Just thought I'd document the pulsing....... I knew that wasn't normal.
    Still tempted to do just the pump.....just to see what happens.... might do that then still do the master after testing it.....not putting it back together just bleed and see if it runs. Would be silly not to do both since I have them. I actually have 3 pumps..... and I have 2 complete egr systems also.
     
  12. rjparker

    rjparker Senior Member

    Joined:
    Jun 6, 2008
    2,210
    940
    1
    Location:
    Texas Hill Country
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
  13. Tim Jones

    Tim Jones Active Member

    Joined:
    Jul 17, 2018
    779
    307
    3
    Location:
    SE Texas
    Vehicle:
    2013 Prius v wagon
    Model:
    LE AWD-e
  14. Tim Jones

    Tim Jones Active Member

    Joined:
    Jul 17, 2018
    779
    307
    3
    Location:
    SE Texas
    Vehicle:
    2013 Prius v wagon
    Model:
    LE AWD-e
    Supposedly 53,000 and a total of $215.00......... and off a Lexus
    s-l500.jpg
     
    #14 Tim Jones, Feb 11, 2020
    Last edited: Feb 11, 2020
    ozjimjam likes this.
  15. Tim Jones

    Tim Jones Active Member

    Joined:
    Jul 17, 2018
    779
    307
    3
    Location:
    SE Texas
    Vehicle:
    2013 Prius v wagon
    Model:
    LE AWD-e
    Ya...it never did it before.......
     
  16. johnHRP

    johnHRP Junior Member

    Joined:
    Aug 6, 2014
    48
    13
    0
    Location:
    tally, fl
    Vehicle:
    2008 Prius
    Model:
    ----USA----
  17. Tim Jones

    Tim Jones Active Member

    Joined:
    Jul 17, 2018
    779
    307
    3
    Location:
    SE Texas
    Vehicle:
    2013 Prius v wagon
    Model:
    LE AWD-e
  18. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    10,120
    7,454
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    H᠎i, welcome to PriusChat, where a lot of people come looking for accurate information about their Prius cars.

    The 'campaign ZJB' document linked above applies only to 3rd generation Prius liftback and Prius Plug-in (PHV) cars, not to the v or the c. The end dates vary by model year:

    zjb.png

    So it's already over for 2010s (unless anybody's got one that hasn't rolled 150k by now).

    For 2011s through 15s, it is still in force through August 2021 and then to your tenth year or 150k miles, whichever comes first.

    It is a replacement conditioned on specific failures ("certain internal malfunctions of the brake booster and brake booster pump assemblies"). It is good to remember that in the 3rd generation Prius, those are two different assemblies:

    [​IMG]

    There is a list of trouble codes that may mean the covered failure has occurred. They are codes that can also be set for other reasons. Sometimes a few simple steps of diagnosis will reveal that something else has caused the codes you have, and that replacement of one or even both these assemblies would not be the necessary solution.
     
  19. rjparker

    rjparker Senior Member

    Joined:
    Jun 6, 2008
    2,210
    940
    1
    Location:
    Texas Hill Country
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
Loading...