Braking problem

I'm new to the forums and Prius lingo in general. What is ICE and HSD?

On a more related note to the thread, I should say that the feeling encountered with the loss of brake pressure is not of acceleration, but just a sudden loss of brake pressure. As if you are just coasting. I think you are right Tom when you say that it probably is worse than it is, but I haven't experienced it enough times to be as confident of that. Another thing that I can not say with complete confidence, but yet enough confidence to place it in a post, is that the loss of brake pressure is not a phenomenon that happens only when we are braking and hit a bump. I'm fairly certain this has happened without us hitting any kind of a bump. The next time it happens I will make sure that I make a mental note as to the road conditions at the exact moment. But for now, I'm probably 80 percent sure this has happened on a smooth road surface.

 

Agreed that it is not acceleration. Some people think it is, because a loss of deceleration feels like acceleration. I don't see it as a problem, just one of the quirks of the car.

ICE = Internal Combustion Engine (the gas engine)

HSD = Hybrid Synergy Drive (the whole drive system)

Tom

 

Thank you for continuing to press with your concern. Just because you aren't yet familiar with ICE, HSD and other Toyota-specific hybrid terms doesn't diminish the value of the contribution.

I'm going to be one of the folks doubting that this event happens on flat, dry pavement. Still, the possibility always exists that there is an issue with your car. Please keep track of these events; write down the mileage (odo reading) and the time of day, along with the road conditions, your speed, weather conditions, etc. This information will help everyone process what is going on.

 

When ABS is kicking in or "ratcheting" at 40 times per second, THAT feels weird. But it's like the Prius completely stops braking for half a second, which feels SCARY. Find some railroad tracks to go over while braking to try it out.

 

OK, been reading all of this for a while now, and still didn't experience it until today. I was coming to a stoplight and the pavement (ashpalt) was rather bumpy in the road. The cars in the line were slowing quickly at the stop light. I applied the brakes and fealt the same feeling as if the car accelerated (In which I know it did not). I recall this same exact occurence in my Honda Civic Hybrid as well. It is certainly startling, since you feel you lose breaking, but all I did immediately feeling that, was press harder on the brake and it seemed to immediately stop. I could best describe it as the car feeling like it was "Jolting".

I had this happen in my 2007 Honda Civic Hybrid all the time, after rough pavement, or railroad tracks or pothole (especially).

I just hadn't experienced it in the Prius until today, since I have had the car 2 weeks now. It reminded me quickly of the Honda interaction and now I at least know what the "feel" is like in the Prius. I don't think this is at all a recall item or Service Bulletin item, again IMO.

It's just a new learning curve and once you know, you handle it differently. I recall an older car of mine doing that (Non Hybrid) especially when hitting a manhole or pothole.

Just my observations.

 

Since I am quite certain, but again not 100 percent so, that this (a sudden and brief loss of brake pressure) has happened on a flat, smooth, and dry surface, I will certainly begin to start taking detailed notes of the above mentioned conditions when this phenomenon occurs. As long as it's okay for me to post the findings here, I will do so. I don't want it to appear like I'm hounding the condition, but I just sincerely think there is more to it here and that it may be a safety concern for all owners of a 2010 Prius (and perhaps earlier years as it sounds as if this is not a new thing). I do not believe that it being "regular" or "normal" diminishes the fact that it could very well be a safety concern when it comes down to a half second difference of running over a child darting out in front of you or just almost running over him/her. Not to mention the mere peace of mind that it would give me, and other drivers, of wondering if the next time you hit your brakes you're going to lose brake pressure.

 

I experienced this today for the first time. Definitely a strange feeling. But so glad I read here because I knew exactly what it was.

 

i have owned 3 Pri's and they all do it. try driving over a manhole cover on a roundabout after a bit of rain. that is ALWAYS exciting. and what the heck?... a little something to get the heart going once in a while never hurt anyone and if it did, its only a matter of time anyway

i have experienced it so many times, i often can tell which tire is doing the slip. and once again, despite the very uneasy feeling of sliding out of control, i think you will find that the variance in your tracking line to be very small.

 

I haven't experienced this yet (and I'd be just as happy not to), but, as you've just mentioned, knowing a bit about the phenomenon and circumstances surrounding it are a big help. So, thank you. This is my first Prius (or any hybrid) and I'm happy to be part of a community that makes the learning process enjoyable rather than a frightful chore.

Cheers
Tim

 

Hi Revelation ... , et al,

You are not loosing braking pressure when this happens. Its actualy increasing, as during regeneration there is little to no hydraulic pressure, and during friction braking the pressure is similar to a standard system. But braking power is reducing because the regeneration system is more powerfull than the friction brakes, when the friction brakes are rusty, cold or wet.

Applying more pressure when you feel less braking power is doable with experience, just like subconciously lifting on standard brakes just before they grab as one comes to a stop. Which I know I did. In fact, on heavy-vehicle rippled road while turning, I would modulate standard brakes to keep the front of the car level. Older cars had cast-iron blocks, and would benefit from this action.

With regards to a pedestrian situation, if the road is not going to provide the stoping power required, well, maybe a slower speed is neccassary. The reason the car is switching to friction brakes, is it has sensed slipage.

If your foot is on the gas just before stabing the brake, the Prius will activate the brakes quicker than standard cars, and apply more pressure to the brakes than you are physically capable of. If your foot is on the brake and you press harder, this action is not as impressive.

 

I am surprise no one mentioned this yet.

Increasing tire pressure beyond the recommended PSI would increase the chance of traction control being triggered.

Try running at the recommended PSI and see how much it improved.

 

I hate to sound repetitive here, but again I must point out that this has happened to me on a smooth and dry surface. The car is a month old, so I'm quite sure that my tire pressure and tread are not an issue. It's as simple as the brakes just randomly loosing pressure. I'm starting to feel like I'm the only one who's experiencing this on normal road conditions.

Regarding the above quote, if there is little to no hydraulic pressure, would that not be a loss of brake pressure? Doesn't the car primarily use regeneration brakes unless friction brakes are needed? The above two questions are my assumptions, so please correct me if I'm wrong. I've also heard from other sources that the opposite is true regarding which braking system is more powerful. I've been told from multiple sources that the friction brakes are more powerful. Then again, you point out that this would be the case if the friction brakes are rusty, cold or wet. But then again, I would have bigger problems if my friction brakes are rusty, cold or wet when the car is barely a month old and it's a warm, fairly dry summer in Indiana.

So again, I must ask, what would randomly cause cause a loss of brake pressure for one half to a full second on a smooth, dry surface? I can accept that it might be the car is suddenly switching between the two different types of brakes, but what I'm gathering so far is that this should only happen if there is a loss of traction. Since I've posted the original inquiry, it hasn't happened again yet. But it's only happened a few times since I've had the car. As I've mentioned before, the next time it happens I'm going to take detailed notes as to the exact road conditions and, if possible, I'll snap a photo of the spot where the brakes lost pressure for visual proof. I'm that sure that this is not related to traction in all cases.

 

Thanks Travis for continuing your discussion. I too have experienced the sudden loss of braking several times as you described.

I've owned my Pkg II for 6 weeks, drive it every day and loving it. As an engineer by profession and a computer geek, I love the techno features in the car, thanks Toyota.

Maybe I need to become more accustomed to operating this car but I don't care for this type of braking performance, seems like an "oops" in a well-designed car! Maybe the computer needs a software update, Toyota what says you?

 

Yes, I have. Left four skid marks as well. Thankfully the "pause of terror," didn't leave matching ones in my knickers.

 

happened to me today! makes me want to return the damn car because i'm going to have my newborn in it! i'm going to call the dealership tomorrow and figure it out. i'll let you guys know!

 

this really killed my confidence in the car because i bought it thinking it was safer for us. i know it's a computer on wheels but i shouldn't be driving the beta version of the software out on the road like that. you figure with all the testing they do prior to releasing the car to the public that they have it all figured out already!!! after i go get it checked out tomorrow and if i don't feel good about it or have an ounce of peace of mind....it's going back! it's no longer a clean slate with me. i'm just a little bitter because i bought the car thinking it's was safer than the 03 civic that i traded in for it. okay okay.....not a little bitter....i'm bitter. i'm just a little spooked because i don't want that s#$t happening to me in any other phase(i'm a airline pilot) of driving.

 

I just looked through the manual on "braking", on p. 246 these pieces of additional information on the traction systems are included:

"
"[FONT=Arial,Arial][FONT=Arial,Arial]Sounds and vibrations caused by the ABS, brake assist, TRAC and Enhanced VSC[/FONT][/FONT]
[FONT=Arial,Arial][FONT=Arial,Arial][/FONT][/FONT]
[FONT=Arial,Arial][FONT=Arial,Arial]
Any of the following conditions may occur when the above systems are operating. None of these indicates that a malfunction has occurred.
• Vibrations may be felt through the vehicle body and steering.
• A motor sound may be heard after the vehicle comes to a stop.
• The brake pedal may pulsate slightly after the ABS is activated.
• The brake pedal may move down slightly after the ABS is activated. "

I've posted before that I've had no regenerative or general brake issues since June with the Prius, nor with a prior Lexus Hybrid I had for 3 years. Is the bold item (I added the emphasis) above something that may be happening here? When my ABS has been activated on my other cars, I've felt a pretty strong brake pulsation feedback that may well have masked any change in pedal stroke, but if the Prius has just a slight pulsation, maybe what folks are perceiving as a "pause" is just this movement of the pedal as the ABS revises individual brake line pressures. By improving the feel of the pulsation (since the earliest ABS systems' more aggressive pulsation tended to cause people to relax their brake pressure rather than apply more pressure) maybe they masked the activation of ABS?

ABS does not reduce stopping distance (that's also in the manual as a "caution" on page 247), but it does let you maintain steering control during a panic stop. Any comment on this theory?
[/FONT][/FONT]

 

I just wanted to drop in and say that I just experienced this braking issue and its a serious problem.

I was in the city and had to slow down for a bus cutting in. It was definitely not more than 20mph when I had to brake while going over a slightly sunken in sewer cap.

The switch between regen and friction did not take a fraction of a second like it should for safety. It was more like 1 full second where the car was not slowing down when it should! (this was not an ABS issue). It was like the car coasted forward in neutral for a second.

The guys at toyota seriously needs to fix this programming glitch.

 

Just curious, do you right foot brake, or left foot brake?

 

There was an earlier question about which braking system is stronger. Friction brakes are more powerful than the regenerative system. Regenerative braking is limited by the generating capacity of MG2 and by the ability of the HV battery to absorb charge. Also, friction braking is applied to all four wheels, where regenerative braking is done by only the front wheels.

Tom