Brake Booster (electric motor) Cycling Abnormally recently..

So I have a 2015 4x4 Tacoma Offroad with 50k miles. Relatively low miles. Recently I noticed my brake booster motor turning on too much. After 1 or 2 pumps of the brake the booster or accumulator motor cycles and I feel a buzzing in the brake pedal. I have owned the vehicle for 4 years and I never noticed it cycling while driving ONLY at startup.

Last night I changed the brake fluid and bleed the entire brake system just for good measure. I even used Toyota TIS software to do the special bleeding procedure and still no luck...

I had CPO warranty that just expired a few months ago. Thinking about contacting Toyota Corporate for a good will repair.

I know some will reply and say this is normal.. This is not normal.. I have owned a Toyota 4x4 with the same booster for about 10+ years now.
I had a 2009 4x4 4runner with the same booster and never had this issue. My friend with a new Tacoma does not cycle this much either. Even tested out another friends 2018 4runner. Do not cycle when pumping 10+ times...

Any advice?

 

There have been one or two times on my 2013 TRD OR 4x4 auto that the brake booster accumulator motor for whatever reason was much louder / vibrated more than normal.

Give this a try. With the truck completely off, pump the brakes slowly till the brake pedal feel changes (it will be very obvious when it changes). This depletes all of the built up pressure in the accumulator. Let it sit overnight depleted. The next morning when you go to drive it, turn the key on and wait till it fully pumps up the accumulator (takes about 15 secs or so) then start the truck.

Mine will and has always cycled at 2-4 pumps of the pedal depending on how hard you push FYI.

 

Thanks, I'll give that a try tonight.

Definitely 2 pumps is not normal. I tested out this out in a 2022 Tacoma and and 2018 4runner. Didnt happen on 2 pumps.

I'm very particular about noises and I never noticed the pump running while I drove for the last 4+ years. I definitely noticed it run on turning on the ignition which is normal. It might of ran while I was driving before but to the point where you cannot feel or hear it. Now I can feel it at the brake pedal whenever I brake. Its pretty annoying.

 

So just want to give an update so it can help out others.

Below is a series of events.

- Flushed my entire brake system with 1.5 quarts of new DOT3 fluid. Drove around for a month and brake buzzing still present.

- 3 weeks after the brake flush took it to the dealer for kicks, they said brake buzzing is not normal and need to change brake booster. $4k repair. Declined.

- My front brakes needed to be replaced. First time replacing my brakes at 45k miles on the truck. Bought front OEM pads, and OEM front rotors. When changing my brakes I noticed the drivers front caliper piston would not compress in. Damn.. seized piston weird since I live in SoCal where the climate is very easy on the brakes. Should not happen here. Ordered a brand new brake caliper from Toyota also bought 1 quote of OEM Toyota brake Fluid. Bled the crap out of the piston when installing. Changed brakes, all good. I feel no difference in stopping power between one seized piston and a brand new caliper. Whatever. Brakes work fine, but buzzing sound and vibration at a stop continued.

- Following weekend went on a 600 mile off road camping trip. Noticed on the way home from the trip my brakes stopped buzzing. Weird. I even pulled over at the side of the road and started to pump my brakes at a stop. No sound, cant feel any vibration at the pedal or here the pump running. Get home confirmed the problem went away.

Observations:

- Now my brake accumulator runs very quietly like it did before so I cannot notice how many times it turns on after pumping the brake. Runs super quite. Not sure what fixed it? Was it the seized caliper that caused the issue? I doubt it? Was it flushing the crap out of the brake system? I doubt it also because I have a low mileage vehicle..

- Many have said here the brake buzzing/vibration at a stop is normal. It is NOT NORMAL. In a good working system you should not even hear the brake accumulator come on when driving the car. A louder than normal brake accumulator = brake buzzing.

- Normal working brake system you CANNOT hear or feel the accumulator cycle even when you are idling. The only way you can hear it cycle is when you get out the truck and listen under the hood.

- 1 -2 pumps of the brake pedal turns on the brake accumulator = normal (even verified this with 2 other Toyota's)


So now my truck is like it was before. I cant even hear the brake accumulator much when driving or even starting the vehicle. It is super quite without any brake pedal vibration.

 

FWIW, mine did something similar once, but it was like 4-5 pumps then it would freak out. Did it for a few days, then just stopped and never did it again.

 

I'm having the same problem. Owned the truck since new, never heard the accumulator before, had the driver's side rear wheel bearing changed last week and now I'm experiencing what you have described. Went to dealership, and got the same recommendation, brake booster swap is recommended. I'm afraid that's not going to fix it. We'll see. I don't feel safe driving the truck...b/c the brake pedal never felt like it does and I never heard the accumulator go off, now it goes off at start up and every time I brake. Brakes have been bled, ABS system has been bled, etc.

**EDIT - the ABS system has not been bled.**

 

What year and how many miles is your truck?

I would try to do a FULL brake fluid flush with OEM Toyota Fluid. I would flush out 1 quart on each corner. Also I would check to see if you need front pads replaced at well. If you go to the dealer have them do the Toyota Techstream Brake Flush Procedure as well.

My brakes are still good and buzzing has not come back. *knock on wood*

 

These things can fail. I think as we see the 2nd gens age we will begin to hear of more failures. When I had my GX470, the older style electric brake booster on those would fail on people who had 04-05’s. Some people with the redesigned electric booster also were having failures in the 05-09 year range. Enough failures for some guys to open up eBay store fronts and sell rebuilt boosters. And those aren’t that much different than the TRD-OR tacos.

But typically these were heralded by the brake system taking too many pumps to build pressure and buzzing, and whatnot until the booster finally fails and throws the vehicle in limp mode with barely any braking power.

 

Thank for replying. When reading your response I realized my original post was incorrect. I indicated the ABS system has been bled, it has not. My fingers got ahead of my thoughts.

2013 TRD off road, 143k miles. Last changed the brakes and fluid at 120k.

 

Thanks for replying. After reading several threads tonight, with the truck off I pumped the brakes until the pedal felt different, as in it had alot of give and bottomed out (about ten pumps), turned the key to accessories, and the accumulator 'charged up'/made the noise referenced in these threads for about 15 seconds. Turned the truck off and repeated the process three more times. I then started the truck and the brake pedal felt like it always had, so I went for a drive, and the accumulator never went on again for the duration of the drive. 10 miles around town, stopping at lights, slowing down for traffic, etc. If it did go on, I could not hear it like I have been since this problem started.

I'm assuming tomorrow morning, I'll start the truck like normal, and I'll be back to square one. I'm not convinced the accumulator is faulty b/c it pressurized as it should after I bottomed out the brakes.

...but maybe it has failed and it's time to replace it. Will be my first issue with the truck since I bought it new. Not a bad thing.

 

Your truck is does not have too many miles for the Brake Booster to go bad.

This is from the Toyota Service Manuals. I did extensive research on this topic. Unfortunately Toyota in all their literature (I paid a subscription fee to get the most up to date informatuon) and Toyota during the troubleshooting never once mentions buzzing in the break pedal or abnormally loud accumulator in their Problem Symptons Table.

Try this. From Toyota

INSPECT HYDRAULIC BRAKE BOOSTER ASSEMBLY FUNCTION

(a) Inspect brake booster pump power supply system function.
(1) Turn the ignition switch off.
(2) Depress the brake pedal 20 times or more to release the pressure in the accumulator.
HINT:
When the pressure is released, the brake pedal stroke becomes longer.
(3) Check that the brake fluid level is at the MAX level.
(4) Chock the 4 wheels and release the parking brake.
(5) Turn the ignition switch to ON and measure the brake booster pump operating time (the time from when the brake booster pump starts
operating until it stops).
OK:
20 to 80 seconds
(6) Start the engine after the brake boost pump stops.
(7) Check that the ABS warning light and slip indicator light are not illuminated.
(8) Turn off the engine, and then turn the ignition switch to ON.
(9) Check that the brake boost pump operates and then stops when the brake pedal is depressed 4 or 5 times.
(10) Depress the brake pedal 4 or 5 times and measure the brake booster pump operating time (the time from when the brake booster pump
starts operating until it stops).
OK:
2 to 11 seconds
(11) Check that the brake warning light illuminates and the buzzer sounds when the brake pedal is fully depressed continuously 15 to 20
times.
NOTICE:
Wait 120 seconds or more after turning the ignition switch to ON before performing this inspection.
(b) Check brake booster operation.
(1) Turn the ignition switch off.
(2) Depress the brake pedal 20 times or more to release the pressure in the accumulator.
HINT:
When the pressure is released, the brake pedal stroke becomes longer.
(3) Depress the brake pedal, start the engine, and check the change in the brake pedal height.
OK:
The brake pedal moves slightly inward.
(c) Inspect brake master cylinder fluid pressure change

Accumulator
Sensor
Accumulator pressure sensor reading /
min.: 0 V, max.: 5 V
3.58 to 5 V
If value constant regardless of pump operation, accumulator pressure
sensor malfunction suspected.

If you have TIS you can read these voltages ^^ in real time. All my voltages and everything was in spec but I still had the buzzing pedal. Go figure..

 

Also before I made this thread I did not know much about the Brake Booster.

The Title of this Post is inaccurate as 1-2 presses of the brake pedal cycles the accumulator. This is normal.