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Toyota Prius Brake Problems



  • wwestwwest Posts: 10,706
    edited March 2010
    Directly from the factory shop/repair manual for the 2008 Prius.


    (a) Electronically Controlled Brake:

    The skid control ECU recieves signals from the pedal stroke sensor, master cylinder sensor and wheel cylinder pressure sensor. Based on these signals, the skid control ECU calculates the necessary braking force for each wheel. The necessary hydraulic pressure braking force is sent to the hybrid control ECU via CAN communication. The skid control ECU receives a braking force (regenerative braking force) signal from the hybrid control motor via CAN communication. The ECU calculates the necessary hydraulic pressure braking force based on the necessary braking force and regenerative braking force.

    Rephased/structured for clarity:


    (a) Electronically Controlled Brake:

    The skid control ECU recieves signals from the pedal stroke sensor, master cylinder sensor and wheel cylinder pressure sensor.

    Based on these signals, the skid control ECU calculates the necessary (TOTAL) braking force for each wheel.

    The necessary (TOTAL) hydraulic pressure braking force is sent to the hybrid control ECU via CAN communication.

    (In return) The skid control ECU receives a braking force (regenerative braking force) signal from the hybrid control (ECU) motor via CAN communication.

    The (skid control) ECU (re-)calculates the necessary hydraulic pressure braking force based on the necessary braking force and (Less the) regenerative braking force.

    So what happens if the hybrid control ECU is "out to lunch" and never sends the results of its calculation back to the skid control ECU...??

    No braking at all...?? :sick:

    Lean on the brake pedal as hard as you wish but unless the skid control ECU opens the ABS/TC manifolds to allow the master cylinder pressure to reach the wheels....
  • PMOPMO Posts: 278
    I am finding through no fault of Toyota ownership most were being told it was new. Then you have the ones that have no idea where to go. There are I would guess a few untrustworthy types as in lottery winners try for a dishonest buck.Then spend time in Jail for the fraud for their deeds.Make sure your kids get them in for any recall NHTSA has a web site for all Toyota recalled cars and has branded them unsafe unless it has been to the dealer for the rework.
  • PMOPMO Posts: 278
    My understanding that until 80% has been applied the braking is sending power to Charge the batteries ? This would leave 20% is this time well spent?
  • wwestwwest Posts: 10,706
    edited March 2010
    When you apply the brakes then the skid control ECU FIRST calculates the TOTAL braking force required and then sends this information to the HSD control ECU. The HSD control ECU then calculates HOW MUCH (0 to 100%) of this TOTAL braking force can be accomplished using regenerative braking. The HSD control ECU then sends its calculated answer to the back to the skid control ECU. The skid control ECU now RECALCULATES the level of hydraulic braking required minus the level the HSD system ECU "said" it could supply using regenerative braking.

    If the HSD control ECU for some reason cannot supply 100% of the TOTAL required braking force then the skid control ECU will begin supplying its portion, %.

    There are two possible "holes" in this procedure.

    1.) The skid control ECU, CLEARLY, will not begin ANY hydraulic braking absent "knowing" what percentage of overall braking it is responsible for. No "message" returned from the HSD control ECU = NO BRAKING.

    2.) Suppose the HSD system control ECU defaults to 100% when in reality it is currently in WOT runaway mode.

    In case #1 absent some sort of timeout on the part of the skid control ECU there might be no braking, EVER. This, the time out, might actually be the "reflash" currently being applied to 2010 Prius models.
  • Have read something like this in the shop manual for 2010, from which my dealer sent me an excerpt. I think I understand the intended workings, but we need your expert opinion, please:

    1. Does the brake system, hardware/software/system control, sound sensible? If not, in what way is it deficient?.

    2. You identify a vulnerability. To your knowledge, has that happened What needs to be done to prevent it from happening?

    3. What would trigger the problem scenario that you describe?

    Thanks as always for your expertise.
  • wwestwwest Posts: 10,706
    edited March 2010
    1. NO...!

    Based on the description given in the shop manual.

    "..what way is it deficient.."

    There is a clear need for a timeout. If the skid control ECU does not recieve a "return" message from the HSD system control ECU within a very short period, <100 milliseconds, it should assume FULL braking responsibility and set a fault code accordingly.
  • wwestwwest Posts: 10,706
    2. NO.

    "...what needs to be done..."

    See above.
  • wwestwwest Posts: 10,706
    3. Most anything. Absent a problem within the HSD system control firmware, race condition, deadly embrace, etc, my best guess would be RFI/EMI.
  • wwestwwest Posts: 10,706
    [quote]If all else fails there is direct hydraulic pressure from the brake pedal.[/quote]

    The documentation clearly implies that the skid control ECU will NOT open the ABS/TC manifold ports to allow hydraulic braking to the wheels if the HSD control ECU "says" it will provide 100% of the braking. So it might not matter how hard your depress the brake pedal the resulting hydraulic pressure may not be ported to the wheels or maybe only a portion provided what the HSD control ECU "reports".

    Yes, clearly there should be, SHOULD BE, a "time out" period if the HSD control ECU doesn't report back within a very short time limit, say <10 milliseconds.

    But if you look at the 2010 Prius TSB regarding the fix for delayed hydraulic braking in the event ABS disables regenerative braking then it becomes quite clear that NipponDenso has overlooked, until now, the need for this type of time out.

    It appears, from reading the TSB, that the early HSD control ECU was sometimes LATE (to busy, too many other more important tasks..??) in responding to the skid control ECU's query and the skid control ECU simply stood by and waited.

    Meanwhile......NO braking.
  • whitey9whitey9 Posts: 138
    edited March 2010
    Not so much. That SBC braking system on the M-B has been eliminated on all but the most expensive cars. It was a "brake by wire" system with a hydraulic back-up system. All we did after that system was released was to try to make it work properly. There were parts modifications, and software update, after software update, after software update. Finally M-B must have decided it was just too "expensive" to have this system of their most popular cars due to all the warranty claims, so it was eliminated on almost all cars except the SL. It was one of those Formula 1-derived systems that seemed like a good idea at the time, but was just too trouble prone. It had a whole bunch of features such as the rotor-clearing during rain, but could not be adapted to passenger cars without constant updates.
  • cgollihercgolliher Posts: 16
    I loved my car before it scared the h--- out of me while taking a turn, lots of rocks on the raod, brakes failed. I am inclined to get it all fixed and sell it immediately. What is know about the cars that have had the recall fix? Any infor would be appreciated. Had a Honda Accord that took that corner almost daily without any trouble, sliding, or braking issues. Darn I wish I had that car back!!
  • PMOPMO Posts: 278
    In conversations with the Canadian Transportation Department,strange things happen .I was told a Motor Home was found to have intermittent problems with transmission shift because a cell phone located above the motor on the dog house (engine cover) another truck Three problems when a new garage door opener was installed . I contend Cell Phones have been on crash sites in more than one case,My Question to you could any of this RF do things to Toyota's software? The other thing Toyota has just sent an Experimental reader to read the Black Box with no instructions,what in your opinion would this mean?
  • whitey9whitey9 Posts: 138
    edited March 2010
    Many years ago, on a 1972 M-B V-8 w/EFI, an owner complained whenever he parked the car at night, in the morning it would crank over but not start. After a myriad of "adventures" it was determined the EFI control unit under the hood was not "shielded" properly. The electrical utility transformer at the top of the pole next to where he parked the car at night was affecting the control unit negatively with magnetic waves. I know that's not radio waves, but they are not too far apart. M-B ( Robert Bosch ) produced a modified ( shielded ) control unit and everone lived happily ever after. Years later we had a problem with some of our cruise control units that were mounted underdash. We "shielded" them w/tinfoil and off they went.
  • I had my 2010 Prius in for the brake repair a few weeks ago and thought it was fixed but I experienced the same temporary brake failure during a soft stop before a stop sign where there is a rill/bump in the pavement. The road is slightly downhill and the ABS is apparently not working properly. I lose a few feet of braking distance when I hit the bump in the road. It's not of great concern because the ABS sensor seems to be consistent in these situations. However, going around a curve on a gravel road would be of concern. I need to report the fact that the software update didn't fix the problem to my local dealer.
  • Ks2010, you are not alone, I have the same problem. I have reported it to toyota, and they tell me the same as they did before, its normal, they can duplicate it on all Prius Models..thats how they work, who wants a car with a defect that the manufacture will do anything but fix it..time for a group to get together..
  • PMOPMO Posts: 278
    Go to NHTSA and the information is there. The thing on Fix for recall is You take it in and it is fixed under that recall. The other thing is if it failles for any reason outside the Recall fix ?
  • PMOPMO Posts: 278
    I contend Toyota has this problem ,the answer is out there. The thing, some thing ( the UAW GM and other things are causing Toyota to have made up this problem, is dumb at best.)
  • wwestwwest Posts: 10,706
    The way I read it the 2010 Prius brake recall does not resolve the issue of the "momentary" (0.20 seconds..?) feeling of "lurching forward" when ABS activation results in a switch from regenerative braking to frictional braking.

    The recall seems to address only the issue of a braking "lurch" of 1-2 seconds or more when the HSD control ECU has other higher priority tasks to perform..

    Driving around a curve on a gravel road in a FWD vehicle under just a bit of acceleration is fraught with PERIL...!!

    So VSC or TC will be highly sensitive in that case. Anyone having previously driven a FWD car without VSC or TC would undoubtedly quickly note the difference in handling dynamics.
  • dasnakedasnake Posts: 1
    I just had my 2010 Prius at the dealer for the brake problem recall. Got the car back yesterday afternoon and this morning on the way to my child's day care....bam! same loss of brakes over the same bump that brought this problem to my attention when I first bought the car (current mileage only 4600). Called the dealer and they are suggesting that this is normal (???) and want me to come down and replicate the problem on the other side of town. Where am I going to find a bump in the road that will cause this problem to reappear in an area that I am not familiar with??? absolutely ridiculous....I have placed Toyota far behind me now and will not purchase another one of their vehicles... I have driven Mercedes, BMW, Chevy, Chrysler...with ABS systems and none had these issues.
  • cgollihercgolliher Posts: 16
    Dear Dasnake,
    Wow, when and how is this all going to stop!!! My advice to you is not to transport your child in this VERY UNSAFE VEHICLE!!! It is so frightening when your loose control of your braking, it is indescribable. Mine is going to Toyota tomorrow for the recall, straight from the auto body shop. I am going to have an intense conversation with the general manager. I plan on having the conversation on the showroom floor. I want all those people considering purchasing a Pruis to STOP and rethink this purchase. I am an RN and I am an advocate for all people!!!! I too have had many vehicle with abs breaking systems without any problems. The problem here is the computer. I believe the brains get "scrambled" when the surface changes on the road. I have driven Fords, Chryslers, Volkswagens, Mercedes, BMWs, and Hondas. Would take any of these over a Toyota. This was my first Toyota and will be my last!!!!! I will gladly pay the high price for gas if it offers me and my family safety. THE 2010 PRIUS IS NOT SAFE! TOYOTA HAS KNOWINGLY AND WILLINGLY PUT UNSAFE VEHICLES ON THE ROAD! TO ALL DRIVERS, BE CAREFUL IF A PRIUS IS BEHIND YOU, IT MAY NOT BE ABLE TO STOP!
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