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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!
 

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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!
Hate to say it, but service department time - I would not call your circumstance normal. Concentrate on getting a scenario for them to reliably recreate the issue if possible. At the end of the day there really isn't much difference in the feel of conventional vs regenerative breaking. In your case it sounds like a brake booster pump issue - but that is just speculative on my part.
 

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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 have experienced exactly the same thing you describe, in curves and as I am approaching stop signs or red lights. I have also posted here as I thought it might be related to the TBS just issued for brakes on the early builds. VIN - Sienna Brakes TSB (Technical Service Bulletin) info. | Toyota Sienna Forum - siennachat.com
I also mentioned that I have noticed that this sometimes happens simultaneously as the gas engine starts for no apparent reason for a fraction of a second about 10-15 meters before I completely stop at a stop sign or at a red light. This is my first hybrid so maybe the engine starting like this is normal, but the brakes going out is not nice. Just called my dealer to get this checked.

Any updates on this from anyone?
 

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Once you slow to a certain speed, regen braking stops and it's only traditional braking. The TSB may make that transition more seamless?
 

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My feeling is that the brakes are fine. They don't feel bad to me. This really seems like a programming/computer issue to me. I am hoping the TBS will fix this. In my case, it happens when driving I am slowed down at about 10 km/h.
 

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Are brakes really that bad? I was also reading the Sienna needs/should have bigger brakes as well.
IIRC, about 40K+ 2021 Siennas are already on the road. If there is anything widespread, or even remotely serious, it would have come out by now. I have ours since Mid Jan. I haven't noticed anything to worry about other than getting to know the character of it. It is no different than what you go thru when changing different cars.

I am not implying at all that there are no anomalies like ones mentioned here. They do need to be checked out by the dealers.
 

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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!
Were you driving aggressive when this happens? Does the car do the same thing in straight line braking?
That's not normal from what you describe under normal driving conditions, however it is possible that if you going fast in a turn and hit brakes the abs kicked in to save you.

Sent from my SM-G960U using Tapatalk
 

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IIRC, about 40K+ 2021 Siennas are already on the road. If there is anything widespread, or even remotely serious, it would have come out by now. I have ours since Mid Jan. I haven't noticed anything to worry about other than getting to know the character of it. It is no different than what you go thru when changing different cars.

I am not implying at all that there are no anomalies like ones mentioned here. They do need to be checked out by the dealers.
Are brakes really that bad? I was also reading the Sienna needs/should have bigger brakes as well.
The people who publish car reviews typically love high performance cars so they compare the minivans with what they expect from a sports car.
The stopping distance for the Sienna was not radically different from the other minivans at 60 mph. Sienna is 148 dry/155 wet; Pacifica Hybrid 145/145; Pacifica 136/141; Honda 136/152. We are talking a difference of about half a vehicle length. The perception-reaction time for an automobile driver can vary from about 0.7 sec (66 ft @ 60 mph) in an expected situation to 1.5 sec (132 ft @ 60 mph) in a surprise situation. Stopping distances are primarily a function of vehicle weight and tire grip so larger brakes won't necessarily reduce the stopping distance. Since they weigh much less, the 60 mph stopping distance for the typical sports car is about 100 feet.
Driver Reaction Time (visualexpert.com)
 

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My feeling is that the brakes are fine. They don't feel bad to me. This really seems like a programming/computer issue to me. I am hoping the TBS will fix this. In my case, it happens when driving I am slowed down at about 10 km/h.
Any luck with getting this fixed? I've had what I think is the same problem. While braking into a turn, the brakes will feel as they are not depressed (even though they are) and the van jolts forward. I've taken it to the dealership, but they were unable to find any TSBs or replicate the problem, so no fix. But now it's happening nearly every time I drive the van. Was your dealership able to help, and did they provide any insight into the problem? Thanks!
 

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I have read about "uncertain brakes", which the article explained as an imperfect balance between decelerating using regen and friction braking. I test drove a Sienna today, and the brakes did feel a little vague and certainly non-linear, but I don't think it's going to be an issue. And, if all fails, it has an automatic emergency brake for ya :)
 

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Any luck with getting this fixed? I've had what I think is the same problem. While braking into a turn, the brakes will feel as they are not depressed (even though they are) and the van jolts forward. I've taken it to the dealership, but they were unable to find any TSBs or replicate the problem, so no fix. But now it's happening nearly every time I drive the van. Was your dealership able to help, and did they provide any insight into the problem? Thanks!
Someone remarked that when this happened to them, it was because their foot came in contact with the accelerator as they depressed the brake pedal.
 

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Someone remarked that when this happened to them, it was because their foot came in contact with the accelerator as they depressed the brake pedal.
I experienced this once, I caught the edge of the accelerator when shifting my toe to the brake instead of picking up my foot and planting it directly on the brake pedal.
 

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Any luck with getting this fixed? I've had what I think is the same problem. While breaking into a turn, the brakes will feel as they are not depressed (even though they are) and the van jolts forward. I've taken it to the dealership, but they were unable to find any TSBs or replicate the problem, so no fix. But now it's happening nearly every time I drive the van. Was your dealership able to help, and did they provide any insight into the problem? Thanks!
I took my Sienna to the dealer, they will apply the brakes TBS since it applies to my VIN. Apparently, there is a part that needs to be ordered to do the TBS, so I am still waiting on the part to arrive.

User2457, did you mention the TBS to your dealer? Mine was aware of it and they had no issue agreeing to apply it.

Someone remarked that when this happened to them, it was because their foot came in contact with the accelerator as they depressed the brake pedal.
This is definitely not what happened in my case. It happened a dozen times and I am certain that it was not me catching the accelerator. To be honest, the issue only happened to me in the first 3 weeks. It hasn't happened for a while. Could it be because of the warmer weather? It was -10 to 0 °C for the first 3 weeks I have owned the car and it has been 5 to 20°C since. I noticed that this was happening during the shift from regen to friction brake and the gas engine would fire up at the same time for some reason. All in all, it is not a big issue, but I wouldn't want this to happen to me in an emergency braking situation.
 

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I took my Sienna to the dealer, they will apply the brakes TBS since it applies to my VIN. Apparently, there is a part that needs to be ordered to do the TBS, so I am still waiting on the part to arrive.

User2457, did you mention the TBS to your dealer? Mine was aware of it and they had no issue agreeing to apply it.



This is definitely not what happened in my case. It happened a dozen times and I am certain that it was not me catching the accelerator. To be honest, the issue only happened to me in the first 3 weeks. It hasn't happened for a while. Could it be because of the warmer weather? It was -10 to 0 °C for the first 3 weeks I have owned the car and it has been 5 to 20°C since. I noticed that this was happening during the shift from regen to friction brake and the gas engine would fire up at the same time for some reason. All in all, it is not a big issue, but I wouldn't want this to happen to me in an emergency braking situation.
Thank you! I did mention this forum and a possible TSB, but they said they couldn't find anything. I'll be sure to bring it up again when I take in the car. As a side note, I'm in a warmer climate and have had the problem occur, so it doesn't seem to be climate related for me.

I'm sure it's not the accelerator and brake being pressed at the same time, as it's happened with both my wife and I and happens nearly every time we drive the van. The only reason we haven't stopped driving it altogether is because the brakes re-engage when we take our foot off the pedal and reapply the brakes. We've left a lot more distance for braking to be on the safe side, but it's quite frightening should they fail during an emergency.

I'll post again when I get back from the dealership. Thanks all!
 

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I'm wondering if this is when the ICE starts then the brake pedal could feel a bit different when the vacuum lines boost changes in the braking system? I know that there is a difference between hybrid (regen) braking and normal brake pad friction type? Maybe it's just the slight feel of switching over between the two? If that's the case, you will have to just get used to that. But what I'm talking about would be when it's in friction mode already, then the ICE starts up, and it changes pedal feel. Like if you have your foot on the brake and your start your car the pedal sometimes shifts if you know what I mean?
 

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I'm wondering if this is when the ICE starts then the brake pedal could feel a bit different when the vacuum lines boost changes in the braking system? I know that there is a difference between hybrid (regen) braking and normal brake pad friction type? Maybe it's just the slight feel of switching over between the two? If that's the case, you will have to just get used to that. But what I'm talking about would be when it's in friction mode already, then the ICE starts up, and it changes pedal feel. Like if you have your foot on the brake and your start your car the pedal sometimes shifts if you know what I mean?
Well, fuel injected engines generate very little vacuum and the Toyota Hybrids have an electric vacuum pump/booster. Any change in pedal feel is due to the electric vacuum pump kicking in as controlled by the ECM upon ignition turn-on, not running the ICE. You can experience this by shutting off the van, pumping the brake pedal until it is hard/firm (vacuum exhausted) then hit the start button, without the engine starting, you will feel the brake peddle soften as vacuum builds from the electric pump. There is not really any perceptible difference between re-gen braking and friction braking, the transition is that good. If someone is experiencing a difference they should go to the dealer for possible TSB application on Siennas manufactured prior to 2/1/21 (rough date - there are details on the forum). My Sienna was manufactured late in April, and has the best brake feel of my prior Toyota Hybrids (2012, 2016, and 2019).
 

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I'm wondering if this is when the ICE starts then the brake pedal could feel a bit different when the vacuum lines boost changes in the braking system? I know that there is a difference between hybrid (regen) braking and normal brake pad friction type? Maybe it's just the slight feel of switching over between the two? If that's the case, you will have to just get used to that. But what I'm talking about would be when it's in friction mode already, then the ICE starts up, and it changes pedal feel. Like if you have your foot on the brake and your start your car the pedal sometimes shifts if you know what I mean?
There is no vacuum involved in the brake system. It uses and electric motor driven pump to provide the pressure. It starts up immediately when you start the vehicle. See the following for a description of the brake system:
Toyota Regenerative Braking (import-car.com)
 

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The brake pump pressurizes the brake system upon opening of the driver door. (before the vehicle is turned on)
 
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