Brake “hiccup” sound.

Sufferin' Prius Envy · 03-20-2005, 10:07 PM

Brake “hiccup” sound.

My wife and I went on a one day fun drive last Friday. We drove up into the Sierra, and up and down several passes . . . 300+ miles in all. The car did just fine, but when we pulled into a casino at South Shore, Lake Tahoe, we noticed that a “hiccup” sound coming from the area under the dash or engine compartment. The “hiccup” would occur when the pedal was slightly pressed, and had nothing to do with how hard the pedal was pressed. The sound was NOT the booster pump, and there were never any warning lights. To me it sounded like the actuator was releasing pressurized fluid with entrained air. (Not a mechanic’s ear here.)

On some of the downhill grades I applied the brakes for long periods for speed control, but not hard enough for the mechanical brakes to engage - just hard enough to increase the regen.

The sound continued for the rest of the trip, but the next morning back in Sacramento - elevation 17 feet - the sound had gone away.

I am of course curious . . .

Was it altitude induced?
Did I overheat the brake fluid and induce air into the system?
Should I not have used the brakes for that long a period? (I know about the “B” Engine Braking mode . . . but that was overkill in that it would slow down the car too much.)

Anyone else have brake hiccups???

xevious · 03-21-2005, 01:23 AM

I think I've had the same thing happen... Hadn't thought to ascribe a biological function to it, though...

I live near sea level, but every time I visit my family in the high Cascade desert (high elevation and colder), the brake system or brake pedal makes a vibration noise when I depress the pedal. The sound is similar to rubbing an inflated latex balloon.

Absolutely no idea what is causing this, but I would also like to know. The service center was not able to get my brakes to "hiccup" - perhaps the rather savage-looking technician scared the hiccups away.

Anyone else?

200Volts · 03-22-2005, 01:29 PM

We just went to Reno-Truckee from Sacramento and noticed the same noise as I released the brake from a dead stop. Temp was 34F and we were sitting for 3 hours in stop & go traffic. Back at Sacramento there was no noise.

MiamiMurphy · 03-22-2005, 05:22 PM

Hi -

Thought I was imagining things but I also have started to hear this noise after driving in hot conditions and heavy traffic - I do not hear it all of the time but it does seem related to the brakes.

Let me know if you find a solution.

Thank you.

ML

prius mdt · 03-22-2005, 07:46 PM

First - I dunno - I've never heard a Prius do the hiccup thing - so this is at best an educated guess...here goes.

Any Toyota with B/A (brake assist) including the Prius has an accumulator with pressurized brake fluid. In the event you are in a panic stop and did not use enough force on the pedal to induce ABS operation, the store of pressurized fluid will be released into the brake system to induce ABS and thusly bring the vehicle to a shorter and more stable stop.

As you drive - (and it sounds like heat in the brake system - which relates to heat in the brake fluid) - pressure can change in the BA accumulator - if heat increases, pressure increases, and the system will bleed off some pressure to return the sytem to a proper level. Is it possible you are hearing this pressure bleed during these events? - Just a theory ... Food for thought...

xevious · 03-22-2005, 10:22 PM

Not for me. The sounds occurs when the vehicle is cold, and seems to go away after driving for 20 minutes or so. Cold and high altitude are the only two significant possible contributing factors in my case, although neither may be responsible.

My situation (and this has happened on three occassions) is this: drive from the Oregon valley to Central Oregon in the winter. Park overnight. Starting with the next morning, the brakes will make a strange noise any time I drive my Prius in that area. Problem goes away upon returning to the soggy, warmer valley.

The sound itself is much akin to rubbing an inflated latex ballon, and occurs when lightly depressing the brake pedal. The sound is not well correlated with the physical pedal displacement, but seems to be generated by an automated part of the brake system.

My evidence for this statement is that the sound is highly stereotyped - it sounds the same regardless of how slowly, quickly, delicately, or forcefully I depress the brake pedal.

Any ideas??

HTMLSpinnr · 03-23-2005, 12:10 AM

Some of us have reported (and some dealers are aware) of high altitude/cold weather combinations bringing out a brake system noise. I'm not aware of any fixes though. It was an annoying, if not embarrasing addition to an otherwise nearly silent car.

xevious · 03-23-2005, 02:57 PM

Thanks, Rick. Glad to know that I'm not alone.

I'll give Toyota a call and report this as well. Better safe than sorry if it turns out to be a defect.

03-20-2005, 10:07 PM	#1
Sufferin' Prius Envy Platinum Member Join Date: Jul 2004 Location: USA Posts: 3,998 My Car: Other Non-Hybrid Model: Package: N/A Thanks: 0 Thanked 3 Times in 2 Posts Friends: 0	Brake “hiccup” sound. Brake “hiccup” sound. My wife and I went on a one day fun drive last Friday. We drove up into the Sierra, and up and down several passes . . . 300+ miles in all. The car did just fine, but when we pulled into a casino at South Shore, Lake Tahoe, we noticed that a “hiccup” sound coming from the area under the dash or engine compartment. The “hiccup” would occur when the pedal was slightly pressed, and had nothing to do with how hard the pedal was pressed. The sound was NOT the booster pump, and there were never any warning lights. To me it sounded like the actuator was releasing pressurized fluid with entrained air. (Not a mechanic’s ear here.) On some of the downhill grades I applied the brakes for long periods for speed control, but not hard enough for the mechanical brakes to engage - just hard enough to increase the regen. The sound continued for the rest of the trip, but the next morning back in Sacramento - elevation 17 feet - the sound had gone away. I am of course curious . . . Was it altitude induced? Did I overheat the brake fluid and induce air into the system? Should I not have used the brakes for that long a period? (I know about the “B” Engine Braking mode . . . but that was overkill in that it would slow down the car too much.) Anyone else have brake hiccups??? __________________ My words are my word. I refuse to actively participate in any forum where my written words can/are changed by the powers that be. If you don't like what I wrote, delete it – but don't put words in my mouth that aren't mine. Good-bye.

03-22-2005, 07:46 PM	#5
prius mdt Join Date: Mar 2005 Location: Richmond VA Posts: 25 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	Re: Brake “hiccup” sound. First - I dunno - I've never heard a Prius do the hiccup thing - so this is at best an educated guess...here goes. Any Toyota with B/A (brake assist) including the Prius has an accumulator with pressurized brake fluid. In the event you are in a panic stop and did not use enough force on the pedal to induce ABS operation, the store of pressurized fluid will be released into the brake system to induce ABS and thusly bring the vehicle to a shorter and more stable stop. As you drive - (and it sounds like heat in the brake system - which relates to heat in the brake fluid) - pressure can change in the BA accumulator - if heat increases, pressure increases, and the system will bleed off some pressure to return the sytem to a proper level. Is it possible you are hearing this pressure bleed during these events? - Just a theory ... Food for thought... __________________ Don - Toyota Master Diagnostic Technician

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03-21-2005, 01:23 AM	#2
xevious Join Date: Jan 2004 Location: Oregon Posts: 187 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	I think I've had the same thing happen... Hadn't thought to ascribe a biological function to it, though... I live near sea level, but every time I visit my family in the high Cascade desert (high elevation and colder), the brake system or brake pedal makes a vibration noise when I depress the pedal. The sound is similar to rubbing an inflated latex balloon. Absolutely no idea what is causing this, but I would also like to know. The service center was not able to get my brakes to "hiccup" - perhaps the rather savage-looking technician scared the hiccups away. Anyone else?

03-22-2005, 01:29 PM	#3
200Volts Senior Member Join Date: Nov 2004 Location: Northern CA Posts: 367 My Car: Model: Package: Thanks: 0 Thanked 1 Time in 1 Post Friends: 0	We just went to Reno-Truckee from Sacramento and noticed the same noise as I released the brake from a dead stop. Temp was 34F and we were sitting for 3 hours in stop & go traffic. Back at Sacramento there was no noise.

03-22-2005, 05:22 PM	#4
MiamiMurphy Junior Member Join Date: Mar 2005 Location: Miami Posts: 21 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	Hi - Thought I was imagining things but I also have started to hear this noise after driving in hot conditions and heavy traffic - I do not hear it all of the time but it does seem related to the brakes. Let me know if you find a solution. Thank you. ML

03-22-2005, 10:22 PM	#6
xevious Join Date: Jan 2004 Location: Oregon Posts: 187 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	Not for me. The sounds occurs when the vehicle is cold, and seems to go away after driving for 20 minutes or so. Cold and high altitude are the only two significant possible contributing factors in my case, although neither may be responsible. My situation (and this has happened on three occassions) is this: drive from the Oregon valley to Central Oregon in the winter. Park overnight. Starting with the next morning, the brakes will make a strange noise any time I drive my Prius in that area. Problem goes away upon returning to the soggy, warmer valley. The sound itself is much akin to rubbing an inflated latex ballon, and occurs when lightly depressing the brake pedal. The sound is not well correlated with the physical pedal displacement, but seems to be generated by an automated part of the brake system. My evidence for this statement is that the sound is highly stereotyped - it sounds the same regardless of how slowly, quickly, delicately, or forcefully I depress the brake pedal. Any ideas??

03-23-2005, 12:10 AM	#7
HTMLSpinnr Gen III Forums Moderator Join Date: Dec 2003 Location: Surprise, AZ (Phoenix) Posts: 4,392 My Car: 2010 Prius Model: IV Package: Solar Roof Thanks: 282 Thanked 516 Times in 246 Posts Friends: 18	Some of us have reported (and some dealers are aware) of high altitude/cold weather combinations bringing out a brake system noise. I'm not aware of any fixes though. It was an annoying, if not embarrasing addition to an otherwise nearly silent car.

03-23-2005, 02:57 PM	#8
xevious Join Date: Jan 2004 Location: Oregon Posts: 187 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	Thanks, Rick. Glad to know that I'm not alone. I'll give Toyota a call and report this as well. Better safe than sorry if it turns out to be a defect.