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She said our HH "gap" frequency has dropped significantly since switching to snow tires. This "slip/gap/lurch" normally occurs right from the first cold-morning start. The first gap almost always happen as we coast down our steep driveway. Then twice or thrice more as we hit various stop signs and traffic lights before getting on the freeway. That was the pattern earlier this winter and every winter since 2005.
Now, it rarely happens. I actually cannot remember it happening since we put on our snow tires.
Could it be that All-Season hardens in cold weather and the car is detecting something that we cannot feel in normal driving? So ABS turns on sooner as you suggest?
May be snow tires remain pliable and soft in low temperature so it is less likely to actuate the ABS?
THis is just a wild guess right now. We will try to be more alert about this and report back if we have any concrete repeatable observations.
Since some of us have slightly different symptoms, I would guess that we have slightlt different software updates..
They should hire me! I could fix our wagons... Just kidding
Again, a non-hybrid NEVER applies braking to ONLY the front wheels. In point of fact with a non-hybrid light braking results in more braking capability apportioned to the rear wheels than when moderate or heavy braking is being used.
With a FWD hybrid using regen braking the front wheels, ONLY the front wheels. are being used for braking. Thus I would fully expect one of these hybrids to activate ABS's transition to frictional braking more often than a non-hybrid ABS standard activation, given equivalent conditions overall.
In retrospect, certainly does seem to be a MUCH more common experience in my HH in cold weather compared to warm weather -
Would the theory apply to 4WD HH's like mine? Seems like the same principle (i.e. a pre-emptive move from regen to friction when weather is cold) could apply - in other words, maybe the engineers figured that cold weather = higher likelihood of slippery surfaces, and so write the program to proactively get the brakes ready for ABS to run if needed.
your comment about "gain" made me think of that term in another way. The thing I find disconcerting about the "braking gap" is not the gap itself - it lasts maybe 0.5 sec or so - it's the fact that when the friction brakes kick in after the gap, the "gain" if you will is turned down and the driver has to hit the pedal harder to get the same braking effect.
As I think about it, it would seem that it must be difficult for the engineers to perfectly match the two braking systems in terms of X amt of pedal force translates to Y amt of brake application. Perhaps they programmed the system so that when friction brakes kick in, they will, if anything, apply somewhat more "lightly" than regen? If they had biased the program the other way (friction > regen), the brakes would suddenly apply harder than intended and our cars would lurch to a sudden stop. Of the two outcomes, maybe they figured the former scenario was preferable?
Are you really sure about that...??
Our natural, HARD to overcome, instinct when we feel that "lurch" forward is to immediately apply the brakes harder. Not that it would be easy, but have you ever tried just maintaining a constant brake pressure to see if the frictional brake, once that take effect, comes on at the same braking level...?
Personally were I the design engineer writing the firmware specifications I would want the frictional brake to come online with even more braking ability than was just being used with regen.
But then maybe that's what the new firmware "reflash" does.
Might that actually be a conditional situation based on the current, INSTANT, frictional coefficient of the brake pads themselves..?
For instance the rotors being wet would undoubtedly result in having to press the brakes harder to get the same braking effect.
Regen to frictional braking transition... not an easy firmware specification to write.
Conundrum, for sure.
If some of you are so worried about this "brake" problem, trade your Toyota in for another brand GM/Ford/ect. Don't stress yourselves out and get a heart attack or a stomach ulcer.
As for myself, I will keep my Prius as long as possible to see how many miles I can put on it. Toyota and Honda are are the most reliable brands I ever owned in my 24 years of driving.
I do not believe that braking is happening for that split second with my car. There is a definite increase in speed when it happens. Not a sensation. It goes like this:
1. Apply brake at low speeds-Car slows down.
2. Slippage occurs-Car coasts and speeds up.
3. Brakes re-engage, car slows down and stops. Sometimes an abrupt stop to make up for increased stopping distance.
I have noticed this on totally dry smooth roads. Bumpy roads. Wet roads, snowy roads, etc. All conditions and most times when ABS should not be needed.
Yes, probably the 100 milliseconds or so it takes to open the electrically operated solenoid that controls the ABS pressure porting manifold, and then another 100 milliseconds or so for the hyraulic pressure to "push" the brake pads into firm contact with the brake rotor.
"......ABS should not be needed..."
And if you weren't driving a FWD hybrid most likely "ABS" wouldn't be needed. I would imagine that during regen ONLY braking the ABS's ECU might be more sensitive, higher "gain", to the slowing of a braking wheel. Maybe even moreso, incrementally higher gain as putside temperature falls near freezing level.
The easier, quicker, regen braking slows the wheel(s) the more important it becomes to switch braking modes. A slight bump in the roadbed, slippery crosswalk stripping, a railway rail, anything that results in a braking wheel momentarily losing contact with the roadbed, and regen gets instantly cancelled.
What you are feeling is most likely NOT actual ABS activation, but the "switch" to a braking mode that CAN be controlled via the anti-lock system should the need arise.
Here's what happened:
I was traveling home from business and was heading northbound on NY State Thruway 87 with traffic more to the heavy side but moving smoothly, weather conditions were excellent. Well apparently a goat had wandered onto the Thruway and a tractor trailer driver locked up the brakes to stop for it. The few cars between myself and the tractor trailer quickly moved over to the left lane with the last one swerving almost at the last second. I moved my foot over to the brake seeing that there was probably slow moving traffic ahead and when I saw the truck, it didn't have brake lights or flashers on so it took me a moment to process that he was standing still. Well I had to make a quick decision: the left lane was blocked for me because everyone else had swerved to it, the right shoulder had a guard rail from the underpass I had just went under; I thought I could try to get through the small gap between the truck and the guard rail but I thought I might flip if I hit the rail too hard so I chose to square up on the truck's bumper and stood on the brake pedal and that was at about 90 to 100 yards till impact. Well the anti-locks started out well and I felt 5 to 10 pulses of the brake then (just as all of you have described and we all know happens with this vehicle) the brakes stop and the vehicle is coasting but doing it at 50+mph. The Highlander continues coasting for 40+ yards (1 to 2 seconds as I recall) before the anti-locks start working again but at this time it was too late and I hit the tractor trailers rear bumper at about 50mph and stopped dead (the bumper on the trailer was too high for the Highlander's frame so the bulk of the deceleration occurred at the motor and passenger compartment, 50mph to 0 in about 3 or 4 inches.) The collision guys couldn't believe I walked away from the accident, they told me that 'high hits' at that speed against tractor trailers are almost always deaths or paralysis at best. I am messed up for sure, hands and feet are numb and back and neck are incredibly painful. I have bruises that run from my ankle right up to my knee from the dash board and my right knee split open also from the dash. I had a large goose egg on the crown of my head from where the high hit of the trucks bumper drove the vehicle down. All in all, I shouldn't be here writing this post but could easily be in a funeral home somewhere waiting from my family to have me buried.
I called Toyota several times about this and no one has ever called me back. Last year, after the Prius recall, I wrote an email to the US Department of Transportation telling them that the Toyota 2007 Highlander Hybrid has the very same failure mode (I.e., brakes not functioning consistently during rough driving conditions.)
Reading through the previous posts here, my vehicle did the exact same thing as the rest of yours does. I know of at least three failure modes on my Highlander Hybrid and they have been described here previously but here they are as I know them: 1) the low speed surge while the regenerative braking system switches to friction braking, 2) stopping on slippery roads especially ice and slush, the anti-lock brakes stop functioning and don't work again till the vehicle is almost at rest 3) under rough driving conditions the brakes will stop working for 1 to 2 seconds before re-engaging ... which was the one that resulted in such a bad collision for me.
My advice to those of you who still have Highlander Hybrids is don't except any excuses from Toyota or the dealership. This is Toyota not doing the right thing because I'm sure they are aware of the problem. I had learned to live with the failure modes in the braking system like the rest of you have but one day you might be faced with the same situation as I just was and have to watch a stationary object (like a tractor trailer) come at you like a freight train and know there is nothing you can do about it.
I'll try to post pictures if I can ... pretty nasty looking I can tell you.
http://i758.photobucket.com/albums/xx223/bryankm_bucket/IMG00011-20100528-1047.j- - pg
http://i758.photobucket.com/albums/xx223/bryankm_bucket/IMG00015-20100528-1048.j- - pg
http://i758.photobucket.com/albums/xx223/bryankm_bucket/Highlander2.jpg
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Yes, including the tire treads.....
Keep in mind that you are driving a FWD vehicle that is potentially a very DANGEROUS vehicle to be driving on a wintertime adverse condition, slippery, roadbed. Add to that the fact that your hybrid "wants to" make use of regen braking, FRONT WHEEL BRAKING ONLY, as a priority, a HIGH priority, and you have a somewhat (potentially) deadly mix of technologies.
Loss if traction, even momentarily so, on the driven, FRONT, wheels of your vehicle is a matter that requires INSTANT and URGENT attention. On a standard FWD with TC even the slightest level of wheelspin/slip arising from too much engine torque being used for conditions will result in INSTANT TC activation, engine dethrottling and braking of the engine driven wheels.
ABS is simply the "inverse" of TC, prevention of wheel lockup or skidding MUST be attended to INSTANTLY otherwise loss of directional control leading to an accident it far too likely.
So, with even the detection of the slightest level of impending (IMPENDING) front wheel lockup or skidding due to regen braking the braking mode MUST be switched. Regen braking, FRONT ONLY BRAKING, must be quickly disabled in favor of frictional braking ONLY, front and REAR frictional braking.
So, now, how should that transition be handled...?
The initial application of frictional braking in this instance MUST be, by default, calculated at the factory to be LOWER than the previous regen level. Otherwise we would soon find ourselves in the very same "boat"....impending wheel lockup/skidding and continuing ABS intervention.
So yes, in these instances, transitions from regen braking ONLY to frictional braking as a result of impending wheel lockup detection there MUST BE a transitional period of "lighter" braking. I don't see that the design engineers had much of a choice in this matter.
Your HH might well have the same feature. And/Or more likely the "gain" used to detect impending lockup is increased as the OAT declines below, say, 35F.
It'l be interesting to know how well that works in real life conditions....
In my experience the slight shift of acceleration or lurching forward happens at less than 15mph and maybe at even less than 10mph. It is just very surprising and disturbing when you have to "all of a sudden" add extra braking power as you are coming to a stop.
They will only pay attention to a class action suit unless there deaths (see acceleration problems).
Let's get together and sue them and maybe we'll get their attention!!
During coastdown periods the engine is starved of fuel, FULLY starved, and the transaxle is sequentially downshifted in order to keep the engine turning over above the point of stalling. Once a "too" low speed is reached fuel flow is restored and the transaxle is upshifted. That last bit is why you feel a "lurch forward", due to the "relaxation" of engine compression braking.
The truck slipped in black ice at 60 kmh, and failed to be controlled as the brakes did not even slow down it as there were dry patches too,but i did not have winter tires then.I got this truck repaired on Dec 18th 2012.
The highlander was in the dealership body shop for two months.
After driving for three weeks,Jan 22nd 2013, i had a second accident this at the speed of 25kmh at the play ground zone as the second car ahead stopped with no apparent reason,but my brakes failed again,this time had to apply the brakes hard as the low end delivery truck did and the highlander brakes failed even after pressing hard.
My first cost for the repairs were paid by my insurance and it was $15000
That brake is still running just as hot, as I almost burned another finger checking it. Where do I go from here?
Since you had the rotors changed, the smell could have come from the protective coating on the rotors that keeps them from rusting as they sit on the shelf waiting to be installed. A lot of people also notice a burning or hot smell when you replace exhaust parts. Same thing there. The protective coating burns off, but it's normal. If the brakes smelled hot, it's because they are. That smell will dissipate as the coating burns away. Have you checked the other brakes? I'd wager they may be just as hot and it's just that the smell got your attention and you noticed how hot rotors actually get.
I had a brake pad start to drag on a rotor one time. After about a 10 mile trip to the store one evening, I parked and noticed a hot smell. When I got out and looked at the wheel where I thought the smell was coming from, the rotor was glowing red! So if something was touching as you were driving, you'd know.
Brought it back to dealer last week, they report to me today that I am feeling the transition from regenerative braking to friction braking, and it is normal. In other (my) words, get used to it, this is how this vehicle brakes. For now, I am willing to monitor this issue on this car, since we bought a 1-yr warranty and the braking distance does not seem to be affected. I will monitor this forum and would appreciate any updates about Toyota service bulletins or recalls.
Hope this helps someone!