Is the brake pump always energized?

8AA · 10-30-2005, 06:24 PM

Sometimes, when my Prius is off and locked, I hear on occasion what sounds like the brake pump running for a few seconds. This is not right after shutting down, but rather hours later. Is this a safety feature to make sure that the power brakes are always available, regardless of the state of the car? If this is normal operation, it's not suprising that the auxilliary battery can go dead in as little as two weeks.

galaxee · 10-30-2005, 06:29 PM

ah heck. my husband told me what that was but i forgot.

i THINK it's depressurizing and repressurizing the abs system for some kind of test. i'm sure someone who remembers will post a better answer than my vague memory

hobbit · 10-30-2005, 06:36 PM

Yes, it's always enabled, and runs occasionally to keep pressure
up even after the car's been off for a while. This is the reason
that service information often says to remove both ABS MTR relays
before working on the 12V power system with gear that can't supply
full current to the pump motor.
.
There is some sort of bleed/repressurization cycle that automatically
happens about a minute after the car is powered off. You can hear
this as a sort of hiss, and then the pump runs for a while. After
that it goes into the aforementioned pressure-maintenance mode.
.
_H*

Frank Hudon · 10-30-2005, 07:33 PM

I do believe that after the car is shut off the brake accumulator pump is powered by the ultra capacitor pack in the back of the car and not the 12 volt aux battery.

8AA · 11-01-2005, 05:10 PM

Thanks for the replies. When I'm showing the car to someone and the pump starts up, the person I'm with usually asked what's making that sound. I'm glad I can give them somewhat of an answer other than "I have no idea, the car has a mind of it's own"

DanMan32 · 11-02-2005, 03:17 PM

I think I read somewhere that the pump stops pressurizing after so many hours of being off.

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10-30-2005, 06:24 PM	#1
8AA Senior Member Join Date: Feb 2004 Location: Maryland Posts: 492 My Car: 2004 Prius Model: Package: #9 Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	Sometimes, when my Prius is off and locked, I hear on occasion what sounds like the brake pump running for a few seconds. This is not right after shutting down, but rather hours later. Is this a safety feature to make sure that the power brakes are always available, regardless of the state of the car? If this is normal operation, it's not suprising that the auxilliary battery can go dead in as little as two weeks.

10-30-2005, 06:29 PM	#2
galaxee resident lab rat Join Date: Mar 2005 Location: boilermaker territory Posts: 9,675 My Car: 2005 Prius Model: N/A Package: #5 Thanks: 0 Thanked 94 Times in 37 Posts Friends: 26	ah heck. my husband told me what that was but i forgot. i THINK it's depressurizing and repressurizing the abs system for some kind of test. i'm sure someone who remembers will post a better answer than my vague memory

10-30-2005, 06:36 PM	#3
hobbit Senior Member Join Date: Mar 2005 Location: Bahstahn Posts: 3,625 My Car: Model: Package: Thanks: 0 Thanked 216 Times in 118 Posts Friends: 0	Yes, it's always enabled, and runs occasionally to keep pressure up even after the car's been off for a while. This is the reason that service information often says to remove both ABS MTR relays before working on the 12V power system with gear that can't supply full current to the pump motor. . There is some sort of bleed/repressurization cycle that automatically happens about a minute after the car is powered off. You can hear this as a sort of hiss, and then the pump runs for a while. After that it goes into the aforementioned pressure-maintenance mode. . _H*

10-30-2005, 07:33 PM	#4
Frank Hudon Senior Member Join Date: Jan 2004 Posts: 4,144 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	I do believe that after the car is shut off the brake accumulator pump is powered by the ultra capacitor pack in the back of the car and not the 12 volt aux battery.

11-01-2005, 05:10 PM	#5
8AA Senior Member Join Date: Feb 2004 Location: Maryland Posts: 492 My Car: 2004 Prius Model: Package: #9 Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	Thanks for the replies. When I'm showing the car to someone and the pump starts up, the person I'm with usually asked what's making that sound. I'm glad I can give them somewhat of an answer other than "I have no idea, the car has a mind of it's own"

11-02-2005, 03:17 PM	#6
DanMan32 Join Date: Aug 2004 Location: Tampa Bay, FL Posts: 3,775 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	I think I read somewhere that the pump stops pressurizing after so many hours of being off.