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Hey King Bob, if I was concerned about how my brakes performed on quick application, I'd definitely go to an isolated area where there was no other traffic and do some rapid brake tests to make sure that all was ok. Have you tried that?
 

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My dealer made excuses also, i have gotten used to it and always stop sort of slow, but if i had to apply the brakes quick i would be worried. I am looking for a car or van soon to do a trade on and eat the loss and never drive or purchase a toyota again...always loved toyota but risking my life to drive one is not in the cards for me. Soon i will be calling it quits on the brand although i am unhappy about it loved them till this point and was hoping i fix would come but i have not heard of one and not waiting any longer while i am ahead of having a wreck due to this issue.
Sounds like your mind is made up. Good luck going forward.
 

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Hey King Bob, if I was concerned about how my brakes performed on quick application, I'd definitely go to an isolated area where there was no other traffic and do some rapid brake tests to make sure that all was ok. Have you tried that?
I used to do that on ice/snow to see how my vehicle would brake. Nice big open area and let it rip.
 

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It’s how all hybrid brakes function. People driving a hybrid for the first time just aren’t used to it. They work fine, just differently.

It’s hyperbolic to suggest this van which is WAY over engineered for safety in nearly every conceivable way is putting your life at risk due to nonlinear braking.
 

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For frequent folks here, I am sure you've read 10K times in various threads that we just did 10K Miles trip (DC to Seattle to Las Vegas and many National parks in between over 3 weeks.) So my most recent perspective on this subject is from it too. ;)

BLUF :
1. I have experienced the break transition a few times. On the 10K trip, 3 times.
2. I didn't feel like our lives were ever in danger during this trip. I admit the transition does pucker up your guts a little.
3. I understand everyone has different personal style and tolerance so this is by no mean to imply one way or the other.

We went thru many many national parks, with mountains and twisties. One that really put Sienna's breaks to test was going south on the General's highway from General Sherman Tree. AFAIK, this has to be the longest, twistiest and elevation change road I can think of. See the link to it below. Dragon's tail in Tennessee is well known but I have not been to it. However, I don't know if things can get more twisty and straight up/down like this (Motorcyclists take note ;) ). I didn't feel break transition any time on this descent. When I stopped afterwards, the break smelled really strong. I may have used up good amount of break pad here.

The other road that had me driving with two hands tight looking straight down with eyelids glued open was WY14 going south from Dayton, WY. This is about 60MPH road, and it was raining with us seeing the Sun set while crossing thru the mountains.

Utah 12 and 24 from Bryce Canon to Arches national park are an absolutely amazing mountainous drive too.

Again, I didn't feel transitions during these mountainous drives.

I forgot when the 3 transitions happened, but they were at speeds below 15 or so and not in any sort of risky situation.

Here's link to General's Highway. Check it out.


52015
 

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I don't want to go through this whole thread, but am I correct in assuming this issue is related to the hybrid battery becoming fully charged, and the switch to mechanical braking is too jarring for those not knowing what to expect?
 

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I don't want to go through this whole thread, but am I correct in assuming this issue is related to the hybrid battery becoming fully charged, and the switch to mechanical braking is too jarring for those not knowing what to expect?
Yeah. But not just when fully charged, but when the Sienna is slow enough that it explicitly transitions from Regenerative Breaking to what I guess is to Friction breaking. I recall reading earlier here that it supposedly transitions around 6MPH or so. I wasn't paying attention, but my experience has this happening around 10 to 20MPH and often turning.

When the battery is full, it goes in to Engine Breaking which is typically at higher speed. I don't know if this factor has direct connection, at least not in my experience.
 

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Yeah. But not just when fully charged, but when the Sienna is slow enough that it explicitly transitions from Regenerative Breaking to what I guess is to Friction breaking. I recall reading earlier here that it supposedly transitions around 6MPH or so. I wasn't paying attention, but my experience has this happening around 10 to 20MPH and often turning.

When the battery is full, it goes in to Engine Breaking which is typically at higher speed. I don't know if this factor has direct connection, at least not in my experience.
I'll keep an eye on that. Thanks for your post
 

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This thread seems to be confusing two different behaviors, and pepple seem to converge them into one,
I see at least two separate issues:
1. While braking the transition from regen to traditional braking is a sudden slow down, not a surge.
2. A surge happens when braking and engine decides to turn on to regen battery, this is a surge.

In #2, the feeling is eactly the same as when you idle in park till the battery is low enough for the engine to start. When it starts you feel a surge forward. It is the same thing.

I feel neither is a problem with the brake system that the TSB would address.
 

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Yeah. But not just when fully charged, but when the Sienna is slow enough that it explicitly transitions from Regenerative Breaking to what I guess is to Friction breaking. I recall reading earlier here that it supposedly transitions around 6MPH or so. I wasn't paying attention, but my experience has this happening around 10 to 20MPH and often turning.

When the battery is full, it goes in to Engine Breaking which is typically at higher speed. I don't know if this factor has direct connection, at least not in my experience.
I believe the speed where regen braking starts to transition to friction braking at is approximately 17mph. 6mph was the speed on early Prius, but Toyota found that they needed to have a little more heat to keep the brake pads from deteriorating.
 

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This thread seems to be confusing two different behaviors, and pepple seem to converge them into one,
I see at least two separate issues:
1. While braking the transition from regen to traditional braking is a sudden slow down, not a surge.
2. A surge happens when braking and engine decides to turn on to regen battery, this is a surge.

In #2, the feeling is eactly the same as when you idle in park till the battery is low enough for the engine to start. When it starts you feel a surge forward. It is the same thing.

I feel neither is a problem with the brake system that the TSB would address.
I don't believe that either of the above is what is being experienced.

1) The transfer from regen braking to friction braking does not seem to cause a sudden slow down. Regen braking is very effective, more so at higher speeds. If the brake pedal is pushed hard enough, friction braking will occur when the computer believes that regen braking is not enough.

2) The surge that is described is probably not a surge at all, but a point where the amount of braking force decreases a noticeable amount. The reduction in braking force is seen as a surge because suddenly, the braking force is reduced. I have experienced this a number of times on my car, although not recently. It may be because I am used to it, or it may be because it does not happen any more. The incidents that I noticed always seemed to be at low speed and were near the beginning of a drive. It happened a few times when backing out of my garage (at very low speed). I have no firm data on this, but the incidents that I noticed could be attributed to a slight bit of condensation on the rotors, causing the expected braking power to be lower than what the computer expects. Others may have had different experience.

3) The TSB for the early cars is related to proper calibration of the brake pedal sensor. Apparently, the calibration was not done properly at the factory and was causing people to experience braking inconsistency issues as have been described in this thread.
 

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I see I'm not the only one having this issue. The most common time I experience it is when I'm getting off the highway and gradually slowing down on the off ramp. There are usually cars stopped waiting for a light at the end of the ramp. The first time this happened to me was at the worst possible time. Right as I was slowing down to stop behind the last car waiting in line it felt like the brakes went out and I had to press on the brake pedal very firmly to keep from rear ending the car in front of me. Very scary. The change in acceleration is enough to jerk your head back a little. Now I make sure I get my speed well down early and kind of creep up to the stopped cars in front of me. I had the brake TSB applied months ago. That seemed to address another issue I had with the brakes being very "grabby" when coming to a stop but not this issue. My memory is not that great anymore but I don't think I actually experienced this issue until after the TSB was applied. It almost seems they might have corrected one issue and caused another.
 

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We've had our new 2021 Sienna for just about a week now and have loved it! No complaints except for an issue that has come up sporadically and only 3-4 times this week. When slightly braking for long, drawn out stretches there have been several times when the brakes let up. Not completely but it's as if my foot let up on the brake pedal when it didn't. It's happened the most recent 2 times during a turn and I felt like I was suddenly speeding up into the turn, even though my foot hadn't changed pressure on the brakes. Regenerative brakes are new to me so the first few times I wrote it off as being not used to Hybrid Brakes, but I'm confident now something is wrong. It's as if the computer is deciding to switch from Regenerative to conventional braking, and then not pairing the two the the same level. I have no idea if that's what's actually happening, but it's my only thought.

Is anyone else experiencing this? I know Consumer Reports commented on the brakes and mentioned a TSB was issued, but I haven't heard any mentions of this particular situation. They feel over responsive and linear, except for these 3-4 instances where it just let up.

Thanks for your thoughts and advice!
I was driving on the right lane of a 2 lane slightly curving road and all traffic was stopped on the left lane.
A woman driving a Tahoe type suv on the other direction decided to drive across our 2 lanes to enter a parking and assuming there was no traffic coming on my lane, I saw her and hit the brakes as hard as I could but there was no tire screeching no hard breaking and the van was stopping as if there was no power brakes.
I kept pressing the brake pedal and have to slightly turn towards the same parking lot to avoid the impact, the woman saw my van until I was almost hitting her truck's right rear 1/4 panel.
I missed her by about 2 inches the most.
There is a problem but I have not had the same issue until today when I was moving very slowly towards a light crossing and slightly touched the brakes to make sure there was no crazy driver eating the light and had a similar feeling but the van was moving very slowly.
The similarities is, the first time was a very slight almost not noticeable left curve and the second time was was a wide 90 degrees intersection also turning left.
We've had our new 2021 Sienna for just about a week now and have loved it! No complaints except for an issue that has come up sporadically and only 3-4 times this week. When slightly braking for long, drawn out stretches there have been several times when the brakes let up. Not completely but it's as if my foot let up on the brake pedal when it didn't. It's happened the most recent 2 times during a turn and I felt like I was suddenly speeding up into the turn, even though my foot hadn't changed pressure on the brakes. Regenerative brakes are new to me so the first few times I wrote it off as being not used to Hybrid Brakes, but I'm confident now something is wrong. It's as if the computer is deciding to switch from Regenerative to conventional braking, and then not pairing the two the the same level. I have no idea if that's what's actually happening, but it's my only thought.

Is anyone else experiencing this? I know Consumer Reports commented on the brakes and mentioned a TSB was issued, but I haven't heard any mentions of this particular situation. They feel over responsive and linear, except for these 3-4 instances where it just let up.

Thanks for your thoughts and advice!
 

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I was driving on the right lane of a 2 lane slightly curving road and all traffic was stopped on the left lane.
A woman driving a Tahoe type suv on the other direction decided to drive across our 2 lanes to enter a parking and assuming there was no traffic coming on my lane, I saw her and hit the brakes as hard as I could but there was no tire screeching no hard breaking and the van was stopping as if there was no power brakes.
I kept pressing the brake pedal and have to slightly turn towards the same parking lot to avoid the impact, the woman saw my van until I was almost hitting her truck's right rear 1/4 panel.
I missed her by about 2 inches the most.
There is a problem but I have not had the same issue until today when I was moving very slowly towards a light crossing and slightly touched the brakes to make sure there was no crazy driver eating the light and had a similar feeling but the van was moving very slowly.
The similarities is, the first time was a very slight almost not noticeable left curve and the second time was was a wide 90 degrees intersection also turning left.
Was the brake pedal pulsing in the first case, indicating that the ABS was functioning? If ABS is really doing its job, there should not be any screeching. If the brakes lock and the tires screech, the brakes are not absorbing any energy and it is just the friction between the tires and the road that slows you down. In that scenerio, all the energy is turned to heat by friction between the tires and the road, the rubber melts, and traction decreases. The ideal situation is for ABS to keep the wheel rotating to maintain traction and have the brakes absorb most of the energy.
 

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Was the brake pedal pulsing in the first case, indicating that the ABS was functioning? If ABS is really doing its job, there should not be any screeching. If the brakes lock and the tires screech, the brakes are not absorbing any energy and it is just the friction between the tires and the road that slows you down. In that scenerio, all the energy is turned to heat by friction between the tires and the road, the rubber melts, and traction decreases. The ideal situation is for ABS to keep the wheel rotating to maintain traction and have the brakes absorb most of the energy.
That was what I was wondering about with the higher speed braking whether the abs kicked in. A lot of time your adrenaline is pumping you may not notice the abs pulsating which is a very odd feeling and it feels like you are not going to stop but more controllable stop then skidding.
 

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That was what I was wondering about with the higher speed braking whether the abs kicked in. A lot of time your adrenaline is pumping you may not notice the abs pulsating which is a very odd feeling and it feels like you are not going to stop but more controllable stop then skidding.
And it permits you to steer which in many situations is just as important as stopping.
 

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Keep in mind the vehicle weighs over two tons. You're not stopping on a dime, there is a Lot of momentum to bring to halt.

Sure, it may feel like it stops well in non-emergency situations. But even when you're foot is to the floor on the brake pedal, it's only using 100%, not the 120% you're hoping to get in your mind.
 

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Keep in mind the vehicle weighs over two tons. You're not stopping on a dime, there is a Lot of momentum to bring to halt.

Sure, it may feel like it stops well in non-emergency situations. But even when you're foot is to the floor on the brake pedal, it's only using 100%, not the 120% you're hoping to get in your mind.
Stupid physics, but the engineers try to control it the best they can for a safe outcome.......sometimes it works better than other times. If this is a repeatable recurrent issue, then back to the drawing board they go to fix or improve the issue. Time will tell if this is a widespread issue or a precieved issue or an individual vehicle issue.
 

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I was driving on the right lane of a 2 lane slightly curving road and all traffic was stopped on the left lane.
A woman driving a Tahoe type suv on the other direction decided to drive across our 2 lanes to enter a parking and assuming there was no traffic coming on my lane, I saw her and hit the brakes as hard as I could but there was no tire screeching no hard breaking and the van was stopping as if there was no power brakes.
I kept pressing the brake pedal and have to slightly turn towards the same parking lot to avoid the impact, the woman saw my van until I was almost hitting her truck's right rear 1/4 panel.
I missed her by about 2 inches the most.
There is a problem but I have not had the same issue until today when I was moving very slowly towards a light crossing and slightly touched the brakes to make sure there was no crazy driver eating the light and had a similar feeling but the van was moving very slowly.
The similarities is, the first time was a very slight almost not noticeable left curve and the second time was was a wide 90 degrees intersection also turning left.

Scary. Glad you came out unscathed.

There are plenty of suggestions here and thoughts. If I were to go thru something similar, I might head out to a deserted parking lot and try to recreate the scenario. If the van behaves anything differently, say a lot better in parking lot, than it obviously needs looked at. If not, I would still get it checked out but at least I know it might be performing as designed. I think a few sites have metrics on stopping distances etc. A lot of factors come in to play, but if you're in ballpark range, it might be ok.
 
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