Stuttering sound when braking - UPDATED WITH AUDIO

Our 2010 Prius makes a "stuttering" sound when braking under certain conditions.

Here are audio examples of this sound: Toyota Prius Braking Noise that Dealership Claims is Normal - Clyp

The sound only happens when we are gently applying the brakes while turning (either direction) at about 10-15 MPH, especially if that turn has even a slight negative (downward) slope.

It's like a clicking sound that repeats 5-10 times with maybe 0.1 secondsbetween each click.

We don't know whether or not it actually has anything to do with the brakes themselves.

The Toyota Dealership performed an expensive brake inspection, and found nothing wrong. They claim we are hearing "the solenoids for the brakes". And that "the solenoids on the Prius are very loud".

Those claims would be more believable if we heard this sound every time we braked. But it does not occur all the time, and only occurs when we are braking while driving slowly and are turning at the same time. Also, it did not make this sound until recently.

Does anyone else's Prius make sounds like this? Any ideas what is causing these sounds?

P.S. That's not our Prius in the photo!

 

Thanks for your ideas.

Have not seen any dash indicators light up when we hear these sounds, but we will be extra mindful to notice. We did wonder if it could be anti-lock brakes activating inappropriately during very gentle braking, but the Toyota Dealersip dismissed that notion.

It happens on smooth asphalt, so it's not a gravel issue. But the wheel speed sensors detecting a difference in wheel speed is an interesting idea. It happens on slow turns that are only 25-90 degrees. Could that still be a possibility?

Regarding the groaning noise, we have heard that a couple times. Freaked us out the first time we heard it. No idea what caused it, and the Toyota Dealership found nothing in their inspections.

 

Thanks for your kind words. Sometimes it's easy to feel like idiots when dealing with this sort of thing.

We asked the head mechanic at the Toyota Dealership the questions, and he just kept on repeating that "it's the solenoids".

Getting another opinion is "just" a matter of more money (which we don't have a lot of). The other Toyota Dealership nearby wants $120 for any diagnostic, whether or not they find an issue. With the Toyota extended warranty about to expire, it's tempting, but the thought of throwing away another $120 on inspections is not a pleasant one.

 

A little over 120K miles.

The sound happens when turning 25-90 degrees, so not typically when the steering is turned full left or right. Given that additional info, does that still sound like a drive shaft issue to you? Thanks!

 

We had a discussion about that. As far as we recall, the sound is relatively new. We started noticing it roughly a year ago.

 

Great question. Our best guess is that it comes from both front brakes.

The Toyota Dealership claims to have performed a full inspection of the brakes, and said they found no issues. We also took it for a test drive with their head mechanic, and he said the sound is the "brake solenoids" and that they are "big and loud on the Prius". He could not explain why they are silent on all braking conditions except when gently braking while turning at lower speeds. He just kept on saying they are real loud on all the Prius vehicles.

BTW, a friend mentioned the possibility of some sort of traction control system misreading wheel speed sensors and thinking a tire is slipping. No idea if that hypothesis could hold any weight.

 

The dealership said there are no codes or pending codes. We just bought a new code reader to verify it.

The Prius never made sounds like this a year or two ago, and makes no unusual sounds when braking while going straight. Do solenoids get louder over time?

 

This page: Toyota Prius Brake Repair, Pad Replacement mentions "solenoids that manage the regenerative braking". It seems like those would be firing at all speeds and not be influenced by the direction the vehicle is turning.

If that site is correct, do you know where they would be located? Would they be repeatedly firing while braking?

 

Using advanced recording techniques (holding a digital audio recorder out the window while driving), we have recorded the sounds.

Here they are: Toyota Prius Braking Noise that Dealership Claims is Normal - Clyp

So, is the Toyota Dealership correct that these sounds are "just the solenoids firing" and that "everyone's Prius makes those sounds when braking"?

The attached recording is from driving down a gradual slope (perhaps 3-5% grade) at 10-15 MPH, making a slight left or right turn, and then braking down to about 3 MPH. We then repeated that process multiple times during the recording. You can clearly hear the clicking sound every time we brake.

Our Toyota extended warranty is getting extremely close to expiring, but with the Toyota dealership claiming that these sounds are completely normal, we do not qualify for any service. We also took the Prius to another dealership, but they were not able to hear these obvious sounds.

We don't want to pester Toyota if these sounds are normal, but our Prius did not make these sounds a year or two ago.

 

You're welcome. Thanks for your interest and help! Here are the answers to your questions:

We tried it with more aggressive breaking, and it does the same thing. We did not try slamming on the brakes.

Travelling down any slope, it is trivial to reproduce. On flat streets, it is sporadic. (We did explain this to the Toyota dealership.)

We just had the dealership perform a full brake inspection, which included the rotors and pads. The measurements were within spec, although a Toyota mechanic at some point got something wrong, because the pad thickness were the same as over a year ago - the Prius conserves pads, but not that much.

Everything is stock, and the dealership performed a full inspection (including undercarriage), so nothing should be rubbing. Of course, during the last oil change and inspection, the dealership did not even notice that the windshield wiper fluid was empty.