Felt the brake cut-out thing.....

You make some GREAT points about the real value in ABS brakes, which is the ability to steer while in a panic braking situation. And yes, it's technically POSSIBLE to stop faster sans ABS, but it's not at all probable.

Braking is most efficient at the point just before your tires lock up. That is a moving and nearly impossible target for any person to hit - let alone in a panic braking situation.

On a PERFECT road surface, under ideal conditions and with a professional driver, it's possible to slightly beat ABS. How many of your panic braking situations meet those requirements? I'd bet none.

The truth is that in nearly 100% of the time, ABS will not only allow you to steer while panic braking, but it will also stop you faster.

Myth busted.

-Brad

 

why are people buying these dangerous cars? Sheesh, just sell it to some poor joe that loves danger, then go out and buy a car that isn't so dangerous. what is the problem? If u don't like the product, get something else...why is this so hard? If i experienced all these scary situations, I'd at least, AT LEAST, go test drive another car and see if it fits my needs better, ie, is more safe to drive over potholes.

The rest of us love our cars. end of story. YMMV...alot.

 

Exactly. When the ABS kicks on you can hear and feel it. Plus a warning light comes on. I've felt the "phantom brake loss" before and it is nothing like when ABS kicked in on previous car. No warning lights come on at all such as ABS or traction control so I'm thinking this is something besides ABS.

 

I am interested in your comment about a ABS Light coming on?? I don't see that in the owners manual unless you have this correlated to the TRAC light?

I have never seen the ABS light come on other than a self check at start up...I would hope your NOT seeing one...if you are then ???

 

The feel was different than a "normal" ABS activation feel. This felt like no braking at all for about a half a second...not the usual rapid stuttering of ABS.

 

Post was based assuming a light comes on when safety features are activated. Roads and weather are good so haven't had any safety lights come on yet in this car. My old Lumina ABS light would come on when activated - usually a panic stop, never for regular pot holes. Never had ABS before that and it scared the crap out of me the first time. I really should test Prius a little when weather gets bad. Be Prepared and all that.

 

It's in the manual---Prius 2010 manual page 247:
n [FONT=Arial,Arial][FONT=Arial,Arial]Stopping distance when the ABS is operating on the wet or slick roads [/FONT][/FONT][FONT=Arial,Arial][FONT=Arial,Arial]The ABS is not designed to shorten the vehicle’s stopping distance. Always maintain a safe distance from the vehicle in front of you in the following situ-ations. [/FONT][/FONT]l [FONT=Arial,Arial][FONT=Arial,Arial]When driving on dirt, gravel or snow-covered roads [/FONT][/FONT]l [FONT=Arial,Arial][FONT=Arial,Arial]When driving with tire chains [/FONT][/FONT]l [FONT=Arial,Arial][FONT=Arial,Arial]When driving over bumps in the road [/FONT][/FONT]l [FONT=Arial,Arial][FONT=Arial,Arial]When driving over roads with potholes or roads with uneven pavement [/FONT]
[/FONT]

 

The ABS light comes on when the ABS sensor, or other parts of the system, are not working properly. It should not come on during ABS engagement.

ABS is what is releasing your brakes when it sense a lockup at a certain rate of deceleration.

What other system is designed to releases your brakes automatically in the Prius?

 

Thanks, that's exactly my point. Page 247 of the manual says ABS is not designed to shorten stopping distance. How many of us get there? (I do, sometimes, but I'm peculiar.)
But virtually all advertising I've ever seen for anti-lock brakes implies (without stating) that it will usually help you stop in a shorter distance.

 

This has been discussed in many threads, but I guess the newer Gen 3 Prius owners haven't seen the threads in the Gen 2 section.

Normal non-panic braking on the Prius is regenerative whenever possible. This means that MG2 (aka traction motor/generator) is running as a generator, providing braking force and generating electricity that is used to charge the HV battery.

When you are braking and a wheel hits a bump, pothole, manhole cover, etc. the Skid Control ECU sees that the car has a momentary wheel slip. The Skid Control ECU decides to activate the ABS system. However, the ABS only functions using the friction braking system. So, if the car is using regenerative braking, it must switch over from regen to friction braking to engage the ABS system.

The half second release of braking force is when the car switches from regen to friction braking. Some people perceive that the car is speeding up, but in reality, it is just releasing the force provided by MG2. After it switches to friction braking the ABS functions just as it would in any other vehicle.

 

Thanks for the clear explanation, dogfriend. Very interesting.
I have never experienced this switch, but I have to admit 1/2 second of no braking sounds like a long time if you are trying to slow down during that time.

Actually, is this different than the switch from regen braking to friction braking that routinely occurs as the car's speed drops below 8 mph ? In that case the transition is close to seamless.

 

I never feel the transition at 7 mph, but many others say they do. It seems to handle that transition more quickly.

 

I've never felt it, but now I will pay attention.

 

Would there be a situation in which at the same time ABS is engaging and releasing regenerative braking, that the ICE could be coming on to charge a low traction battery? I don't know if there is any relationship here, but if you hear and feel the ICE start up just when you are starting to decelerate and experiencing the transition from regenerative to ABS/friction brakes, could the "feel and sound" contribute to this sensation some call acceleration? Maybe someone with more expertise on the mechanics/electronics of this could comment? I have not had any instance of ABS activation in 5 months on this car, braking has been outstanding and consistent, same as my prior RX 400h. Maybe our roads are too good.

 

That sickening feeling has happened to me 3 times so far and I know for sure that I wasn't going to fast. I do love my car but I guess it's like being in a marriage...... Sometimes there will be (bumps in the road).

 

Does not seem likely to me - if you are already in regen usually the ICE is off or just spinning with no fuel. But I suppose it is possible depending on how you drive. In my experience, the ICE is usually not running because I am slowing for a stop at a stop sign or red light and hit a bump. I try to stay off the brakes except when I need to come to a stop.

 

Advice: don't be rude.

 

I have a similar experience with the brake cutting out over a pothole -- very dangerous. It is a route I drive regularly; the pothole is about 30 feet before a traffic light on a downhill section of the road. I drive the same road with another car that also has ABS and never have this problem in that car. And I clearly stop faster at that spot with the other car.

Today I was approaching a different stop light with three cars in front of me. I was doing under 20 MPH when I applied the brakes -- and nothing happened. There was no pulsing or anything, just no brakes. In the end, I had the choice between hitting the car in front of me or swerving into a fence to stop. I took the latter option and have a nice dent in my bumper. It did turn out to be icy at that spot but I was the only car to have trouble (and I have new tires).

Comparing the Prius with our other car (1999 Subaru Outback with ABS), the Prius ABS system comes on FAR more frequently. With the Subaru, the ABS is obvious -- ratchet noise and a clear pulsating in the pedal. With the Prius, it feels like the brake just stops working and there is no pulsating in the pedal.

My questions: Does this sound like normal Prius ABS behavior or is there a malfunction? If it is normal, is there any way to adjust or disable the ABS? I'd be happier to pump brakes that will actually do what I ask than to have brakes that cut-out inappropriately.

 

For those of with 3rd Gen Prii that are experiencing "brake cut out" I *highly* suggest you visit your local dealer and tell them what is going on and have them submit a product report for a quality concern. This is the only way you will ever get any where with TMC on this issue.

 

Our streets became ice covered a couple days ago and I tried braking on ice for the first time and the wheels quickly locked up with no ABS activation. I was very surprised and pressed the brake pedal much harder and the ABS activated. I have never experienced this in my Odyssey as it activates ABS as soon as the wheels stop turning. I went down the same street the next day and was able to recreate the situation. Gentle braking, which would normally use regen braking only, and the wheels locked up. Push harder on the brake pedal and the ABS kicked it. I also found the pulsing from the ABS to be slower in the Prius than the Odyssey. The Prius seemed to be maybe two pulses/second.