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Highlander Hybrid Brake Problems
Having an issue with the brakes on your Highlander Hybrid? This is the place to work out a solution!
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Will be checking with dealer's shop as well in a week.
Ours seems to occur when applying the brakes after coasting. As we step on the brake for the final stop, there is a slight surge (gap) and then the brakes take hold. It does not happen all the time.
I wonder if it has anything to do with the car switching from "recharge-induced slowing" to actual braking.
mmreid :confuse:
First, as I was returning home, I was descending a l-o-n-g downhill grade ;;; ah, regeneration time ( I was traveling about 50mph). At the bottom of this downhill grade was a stop sign. So, I began breaking at a reasonable distance out. Then, about 20 yards out I hit a short (about 2 feet) rough spot in the road. The brakes released for less than a second and reapplied with out my doing anything. The added stopping distance couldn't have been much. But wonder what would have happened if the rough area would have been, say 10 or 20 feet long?? By the way, the anti-lock brake system did not come on.
Second, I was averaging about 27.3 mpg for about the first 200 miles of driving. Then, before today's short 88 mile trip, I was down to about 26.7 mpg and 300 miles. About 50 of these miles were highway and the rest around town (Stop and go but seveal blocks in between the stops). After todays highway trip at 50-55 mph, I'm again up to 27.4. Unlike the EPA estimates, I'm getting better highway mileage than city. I'm thinking that with a long city type stop and go period, more of the ice gas is used for recharging the battery than is the case during highway driving. In a week or so I am planning a 600 mile trip one way utilizing interstate highways all the way. I'll see what it does at 60-70ish.
I also noticed this sensation of "brake slip" when braking gently after coasting. The slip is so slight and fast, it leaves little time to react. The brakes kick in right after but it is disconcerting the first couple of times.
When braking more decisively, the slip never happens and the car stops quickly.
I wonder if when we brake gently enough, the system is still using regenerative braking and not the mechanical brakes. If so, it seems reasonable that when a tire loses traction for a second, the VDIM shifts power to other tires causing the surge sensation because of power transfer.
It is possible we normally will not feel this function while coasting or with foot on the gas pedal. It becomes detectable when we are on the brakes because the VDIM operates the braking system.
Just a guess. Someone asked earlier if this is a "problem". I think it is worth a call to Toyota for clarification. If nothing else, the call may cause them to research and look into it. If we all call, they will take it more seriously.
ABS....
In the instance you describe your "braking" may have been TOTALLY due to regeneration...
If so, and the front wheel(s) began to slip (no ground contact momentarily..?), even ever so slightly, in that rough spot (gravel, sand..??) the regeneration would instantly cease operation (release the "brakes") to simulate what would otherwise be a true Anti-lock Braking System, ABS, "function".
I quite sure, certain sure, Toyota and Lexus wishes they could perform that very same functionality, absent a quick shift into neutral, with engine compression braking. That would improve the overall safety factor of FWD or front biased AWD vehicles substantially.
An added note: I do not recall seeing (although I must admit I wasn't looking for) the "slip" warning light as the HH manual describes.
The rough spot was just that, rough. I did not even see it with my eyes. No sand or other debris was present. There was a slight drizzle so maybe a tire slip occurred??
I am having very similar results as yours.
We live in foothill type community and so are usually going up or down a grade of some type.
Living semi-rural we are getting about 27 mpg but go strictly highway, up & down some serious grades, using cruise and assiting it on the climb till near top, & we are getting 29.4 mpg.
After highway driving & switching to city we've seen 29.6 mpg. Once we start the semi-rural driving again it drops to 27 mpg or so.
This is all by the dashboard. We've mannually calculated the mileage and found it to be about 1 mpg lower than the dash but we are comparing dashboard to dashboard with our older family vehcile which averaged about 17.1 mpg in these same driving conditions.
I too noticed the vechile "surge" while braking. I could be mistaken but found decelerating a little sooner than usual seems to help.
Another question to ask is if the traction system is really active at speed below 25? The manual says all the electronic safety system activates above 25-MPH. So, does this slip thing happen above 25? or under 25? or both? Has anyone noticed the speed when it happens? I will pay attention next time.
Not being one of our highly skilled technicians, let me explain simply that the braking system on the vehicle is designed to shift from the Regenerative mode to a pure Hydraulic mode as the Highlander slows to around 8-9 MPH. If you are not accustomed to driving one of our hybrids (same on the Prius, too, BTW), the sensation could initially be a bit disconcerting--But it is perfectly normal.
When tmsusa first drove the current generation Prius, he too detected a slightly different feeling from traditional braking--also an amazing ability to "coast" seemingly endlessly without the usual slight engine braking feel on traditional vehicles. Great regenerative forward momentum, and made me more attentive to the sea of cars on the 405 here in SoCal!
Thanks for being a Toyota customer--And as always, if you have any other questions or concerns about your Highlander Hybrid, your Toyota dealer should be able to help. Or give us a call and talk to one of our Customer Experience Center reps at 800-331-4331.
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But it's a bit of a one-man operation now, so certainly can't be everywhere all the time. Now, better get back on-topic before our host boots tmsusa! Thanks for your comments cdptrap.
Has anyone had this issue checked by the dealer?
Larry
Are you refering to situations where you step on the brakes, the car begins to stop and suddenly there is a brief hesitation (1 sec), the cars feels like it is not braking and then quickly it brakes again and stops normally?
This does not happen all the time, does it? Just occassionally, true?
I have had several cars and trucks with ABS, and they all have done that when braking hard on ripples or washboard roads.
It is because the computer gets slightly confused when the tire loses contact with the ground, and the tire loses contact with the road then regains contact with the road over and over and over multiple times in very rapid succession during braking over that type of surface because of the bouncing that the surface causes.
My recommendation is to plan ahead and slow down more before those surfaces and the ABS will not bother you as much.
That always seemed to help in my cars.
Ford was awarded a US patent that addresses this very thing with regard to regenerative braking on the front wheels of a hybrid vehicle. The patent specifies reducing the regenerative braking level substantially while the OAT is at, below, or near freezing, and disabling it altogether in any or all conditions the INSTANT ABS activates.
If you browse around on the various FWD and front torque biased AWD vehicle forums on the internet you will find that the industry is striving mightly to solve this very same problem with ALL FWD (and..) vehicles, eliminating the braking effects of the engine on these vehicles so as to reduce the rate of loss of directional control accidents due to loss of stearing capability and from unsafe interference with the functionality of ABS should the roadbed be slippery.
When travelling at speeds under 25 mph, the ABS braking systems do not engage in an emergency stop situation. This has been reported on several forums, including http://www.hybridcars.com/forums/brake-failure-2007-t1013.html, and happened to both me (in a 2006 Highlander Hybrid) as well as my neighbor in her Lexus RX.
In my case, I was travelling around 20 mph on the freeway. The person in front of me unexpectedly came to a complete stop; although I had plenty of space and quickly engaged my brakes, they never "grabbed"--I just slowed and coasted into the car ahead of me. Despite never having been in an accident in my 20+ years of driving, I am now liable for this rear-ender. I hate to think what would happen if a small child ran in front of me on a residential street where speeds are typically under 25 mph.
What is the definition and precise specification of "extraordinary"? 200-lb of pressure?
My wife is a smallish 5-4 and a meager 128-lbs and she has been able to successfully stop this car at low speed (<=25-MPH) without complaints countless times. The only complaint we have is that sensation of "slippage" when the regenerative braking changes to mechanical braking.
At times, when we travel at low speed and with plenty of room in front, we automatically "meter" how we press on the brakes in order to achieve a smooth stop. Were you doing this and the brakes just did not bite as you would expect? Or did you slam on the brakes and they just did not work?
We have had to make emergency stops many times at speed lower than 25-mph and the car have always stopped. This is true even when rolling downhill on our driveway at <10 MPH.
I am not disputing your report, just trying to understand if this is an isolated incident or a potentially bigger problem.
Thanks!
First the issue: We intermittently experience the "braking gap" both above and below the 25 mph mark. It is more apt to happen when the car is cold. We live on top of a hill in the rural / suburban northwest corner of CT. Sometimes when we apply the brakes at 30-40 mph for the first stop sign, half way down the hill, the KW needle goes negative indicating regenerative braking, then the regen braking gives up and the needle goes to zero. To stop the car at this juncture, additional brake force is required to engage the hydraulic brakes. Initially we thought it was a cold car / cold weather issue. We have experienced the the "brake gap" in both hot weather and with the vehicle fully warmed up.
After the last service visit, specifically for this issue, we were told by the hybrid tech that if the high voltage batteries were fully charged that the the regen braking would not engage. We now monitor the battery charge icon. The tech also mentioned that this battery charge icon is not very accurate. The highest level of charge we have seen indicated is a level above the + - signs at the top of the icon. The brake gap usually occurs when the batteries are at least 70% full to full.
He of course explained how the regen braking would disengage at low speeds. I assured him we were not complaining about that operation. We see and feel that, but it is nowhere near as disconcerting as the free fall feeling when it happens at 35 mph. In full accordance with Murphy's Law, it never happens when driving with the tech in the car.
Has anyone had any action from Toyota other than attempt to explain away this issue? Is this still considered "normal" behavior?
You may also want to share your experiences with the following
organizations, which may be able to provide you with information and/or
offer assistance:
1. Center for Auto Safety, 1825 Connecticut Ave NW, Suite 330, Washington,
DC 20009-5708. The CAS compiles information on defective automobiles,
ranging from transmissions problems to paint problems. If you wish, you
may send them a letter sharing your experiences with them. Should they
have any information on your particular automobile, they will forward it to
you, along with helpful information and advice within 10 days from date of
receipt of their letter. They ask, but do not require, a $.60 SASE to help
keep their costs down. Or, you can visit their website at
http://www.autosafety.org.
2. Council of Better Business Bureaus, Inc. at 4200 Wilson Boulevard,
Arlington, VA 22203; 1-703-276-0100. The Council of Better Business
Bureaus, the umbrella organization for the BBBs, also provides programs and
publications for consumers, and helps to settle disputes with automobile
manufacturers through the BBB Auto Line program.
3. Your State Attorney General's Office, which helps to resolve individual
consumer complaints, conducts informational and educational programs, and
enforces consumer protection and fraud laws. You can find their telephone
number in the blue section of your telephone book.
Maybe even replace the control relay with one that has heavier duty contacts, or 2 pole wired in parallel.
Yes, as with mimers' explanation, we have experienced this as well. It does not happen often but once in a while, it does happen. Recently, over the past two weeks, it is happening more often as overnight temperature is now down to 50 or below. This was reported quite sometimes back in 2006 when we all first bought and drove the first version of the HH.
It does seem to happen most often for the first 3 miles. After that, it never happens again. We are also on a hill and shift to "B" for part of the drive and ride the brakes down the rest. It has never happened on this downhill stretch. When it does happen, it is always at one of the stop signs or traffic lights within that 3 mile range.
We went through this whole summer with hardly any problems. I believe WWest mentioned once before in an informative post that it may have to do with the temperature difference. Something that Ford filed patent for? [WWest: is that true?]
Anyway, if any of you pursue this far enough and need extra support or more evidence, let us know with a link or a process and I will be happy to add our experience.
Since it is clearly NOT a good idea to be using regen braking on a slippery surface ABS may be programmed to be even more sensitive to wheelspin/slip as the OAT declines due to the approaching winter.
As a safety measure Ford significantly reduces the level of regen available on the FEH/MMH if the OAT is near or below freezing.
All Anti-lock Braking systems have this "sensitivity", undesirable as it may be.
The "bump" pushes the wheel upward and the shock does not allow it to rebound right away. As a result the wheel loses traction with the roadbed momentarily and the "braked" (Regen ONLY..??) wheel's resulting rotational rate reduction causes an ABS activation.
The only fix would be to disable ABS...
Or modify ABS such that it doesn't activate unless VSC indicates the need. ABS has no functional purpose, NONE, unless directional control is somehow threatened during braking. If the vehicle isn't or doesn't yaw during braking, or the driver doesn't need to make corrective directional maneuvers, ABS activation not only serves NO purpose, but can be detrimental, as can be seen here.
Obviously this effect might be much more detrimental on a modern day FWD hybrid. Up until hitting the bump the braking may be PURELY from Regen, and therefore ONLY on the front wheels. Regen MUST be DISABLED the very instant ABS activates otherwise ABS functionality would be reduced, or maybe even non-existent.
In point of fact since frictional braking may not have been in use AT ALL at the time of the "bump" the instant disabling of same results in NO BRAKING AT ALL until brake fluid pressure can "arrive".
There is an indication, Ford has a US patent concerning this, that the Escape/Mariner/Tribute substantially reduces Regen capability when the OAT is below ~34F to reduce the potential for this happenstance.
Not these days, technology has moved FORWARD.
The microprocessors used to control anti-locking are now fast enough that they can PREDICT when a wheel is approaching lockup, "skidding", based on the rate at which the wheel rotation is decaying.
Have a wheel hit a bump, bound away with no quick rebound due to shock action, and the braking will suddenly become the MAJOR force affecting the wheel rotation rate.
Anti-lock systems are designed to control hydraulic braking via controlling the brake fluid pressure to each individual wheel using the electric solenoid valves. So the only solution for preventing wheel lockup, skidding, due to regen is to disable regen the INSTANT ABS detects impending wheel lockup.
The Ford Escape hybrid was using a F/R brake system split so hydraulic braking could be used at the rear simultaneous with (ONLY) regen braking at the front but it appears that with their adoption of a form of VSC this technique was abandoned.
An ABS "refinement" that is long overdue now that VSC systems are becoming more commonplace.
I suspect you meant to say: "..slid a little before the anti-lock kicked in..."
Provided there was no threat to directional control during that "sliding" period your braking was likely more effective than after ABS activated and began to alternately release and reapply brake fluid pressure.
With a hybrid the initial action of ABS might ONLY be to disable regen. That action ALONE might suffice to remove the impending wheel lockup at the level of hydraulic braking you are currently applying.
So while you would never "feel" the ABS activation via the pulsing brake pedal in actuality it will have completed it task.
"..before I could react on the rain-soaked road..."
"..rain-soaked road.."
Primed for ABS activation.......
With very little experience with ABS we begin to expect that brake pedal throb/vibration the instant ABS activates. But now with a hybrid you have two sources of braking capability. With a hybrid when your Anti-lock system initially detects that a wheel or wheels are approaching lockup/skid/slide (the wheel's rotation rate is decaying TOO rapidly) the first action of the ABS will be to INSTANTLY disable regen braking. It is entirely possible that the disabling of regen will resolve the problem in its entirety and now "you" are left setting there wondering why the braking suddenly got weaker just momentarily.
Following a bit TOO close for conditions...??!!
All this may be true about the ABS and emergency stops, but the "feeling" is there even in a non emergency stop situation or without hitting bumps. I live on a steep hill and generally go down with the intent of riding my brakes to help charge the battery and warm up the engine. It's a long hill, about a quarter of a mile. I drive about 20 - 25 mph during this time. Near the bottom of the hill there is a sharp curve at the same point that the slope lessens. Almost 100% of the time as I approach this area I get the sensation that my brakes briefly quit. However I believe that the sensation I get is the switchover and that it should not be a cause of concern, or at least if I realize this sensation will occur. It is a little unnerving at first, but the HH appears to slow at the same rate.
I liken this feeling to the same one people complained about with the TCH on initial takeoff. Many complained that when they floored the gas there seemed to be a hesitation. In reality, the torque of the electric motor immediately started the car in motion and then the ICE kicked in. They felt the ICE kick in and it gives the sensation that the motor by itself was not doing the job. I believe that to be a feeling, not a fact. The TCH is a quick car, much faster on acceleration than most "sporting" sedans of the 80's. Much quicker than the 4cy ICE only Camry.
It is quite possible that a person could be in the wrong place at the wrong time and the worst happened; all you could remember is that the brakes felt like they gave away briefly.
From what I've learned so far from driving a hybrid, thereare a lot of things with a hybrid they should tell new customers. They should describe some of the quirks and sounds that you will hear, and assure you it's the nature of the beast. It's a different machine than you've had in the past.
Sorry to say this, but my opinion is that if someone slid into the back of another car with the HH, then they were driving too fast or following too close. I don't believe the momentary "feeling" in and of itself whould be a contributing factor in a wreck.
And personally I do not know of ANY road speed and/or road condition wherein ABS should NOT engage.
This slippage is periodic, it seems. I thought it was a bump once, not any more. Then I thought it was temperature but not that either. Now I think it is likely just brakes warming up or something warming up.
Not bumps because it would happen even on perfectly flat asphalt. On a dirt road with pot holes, it does not slip. Not temperature because we have driven in snow and ice and the car did not slip and stopped dead straight on clear ice that we thought were water.
When it does happen, it is often within the first two to three miles after starting from a cold engine. I am beginning to think it has something to do with something NOT warming up. After the first three miles, it never happens again.
Even when it does happen, the car continues to slow and stop as intended. We have never had problems with "run away", at least not yet.
The "slide" I've experienced is very brief and I don't believe it is really anything other than a sensation one feels rather than a performance issue.
As far as being "helpful", 99.9% of the time you run into the back of someone you were driving too close or not paying attention. Hitting deer is a completely different situation.
I was referring to the "bumper tap" post.
Please understand that I think my 06 HH is the best vehicle I have owned. It has brought me on many long trips to Minnesota and back twice, to Branson, Mo. to No. Carolina three times and back safely and without one breakdown. I would buy one again and probably will. As a matter of fact-I am headed this AM to pick up a new Prius because I believe in their technology. I think probably the 2010 is even better but our 09 will have to do for now. Hopefully we will keep our local yota dealer in business and a few salesmen working. My objective is only to keep Toyota painfully aware that this is not something just in our head or a perceived feeling. Thank you all for your patience.