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#304 of 366 08 Prius Brake Failure: Stroke Sensor Malfunction
Apr 26, 2010 (11:56 am)
Definitely hitting an oldie but goodie here. Not to beat a dead horse, but this thread came up as I was investigating a problem my daughter had recently with her 08 Prius and wanted to jump in with our details:
First off, a few caveats - I'm an Engineer, and have approached this in a typical engineering fashion. I'm not an automotive engineer, but I did do quit a bit of MechE studies and earn my living as a Software Engineer, and I've got a pretty good handle on both the mechanical and electrical diagnostics. In addition to the Prius, which my daughter drives, we've got a VW Bora, an Audi Q7 and a Porsche 996, and I'm constantly tinkering with all of our cars to find out what makes them tick and how to make them tick better.
On Saturday, 24 April 2010, my daughter was driving over Hwy 17 to Santa Cruz, CA when she rounded a corner and executed a panic brake due to completely stopped traffic. She was able to keep the car under control and avoid collision. ABS likely was engaged. It's likely that the Stroke Sensor failed at this point. One or more calipers continued to be engaged after she stopped stepping on the brake pedal. She drove another several miles in this state, and experienced brake fade when she tried to come to a stop at a traffic light. When she finally pressed fully on the brake pedal, secondary braking was engaged and the wheels locked. She fishtailed, but was able to maintain control of the vehicle and avoid collision. She immediately parked and called me. Vehicle was towed to nearest Toyota dealer. Diagnostics indicated a DTC C1247 Stroke Sensor Malfunction, but upon electrical reset all mechanical functions resumed normally.
Brake failures are pretty frightening, especially when it's your inexperienced teenage kid behind the wheel. However, I suspect that failures of this nature are fairly endemic to all regenerative braking systems. No extent of mechanical controls would be capable of balancing the engine and brakes, so you've got to trust these things to a computer. And I can guarantee you that all software has bugs, especially around edge conditions. It's simply impossible to test for everything, all you can do is document and learn from your field data.
That being said, I would certainly hope that these situations have been heeded and improved by Toyota. I'm reading stuff here that's five years old, which what appear to be ample field reports. Toyota needs to step up to the plate and take immediate action on this stuff, and stop dismissing it as Edmunds/GM propoganda.
#305 of 366 Re: Brakes failed to stop my 2010 prius and wreck ocurred [cgolliher]
Nov 02, 2010 (5:49 pm)
I have the same problem with my 2010 Prius. It seems to happen more when the weather gets colder. I had the computer "fix" done at the dealer, but it didn't fix it. I bought my car last Dec. & slid through 3 intersections in snowy weather. I'm a very good winter driver, but when brakes release, even for a second or two, when you are stopping on snow covered roads, the car lunges and skids. I start stopping three blocks ahead in snow now because I'm not sure when it will lunge forward.
This is dangerous. I think people in California won't understand because they won't drive in these conditions. I can see where a tight turn on a gravel road would be hazardous with this braking problem as well.
The dealer tells me the brakes releasing for a second isn't a problem and I should learn how to drive with it. At first they act like they don't know what I'm talking about. They know very well what the problem is and the computer flash doesn't fix it. I hope you reported your accident to the NHTSB. I hope everyone does! This is dangerous.
#306 of 366 Re: Prius 2010 Brake fix [hal_cat]
Nov 03, 2010 (6:44 am)
The problem with the brakes releasing is actually happening quite regularly. I'm noticing it more now as the air gets colder. I think some kind of sensor may be involved. I agree about the danger in driving a car with this problem. I wouldn't let my sister borrow my new 2010 Prius because this might happen. It may not be a problem in warmer climates, but in the Northeast it is huge. You don't want your brakes releasing while coming to a stop at a snowy intersection - this happened to me several times- because you'll slide through the intersection (and so I did!). I'm a very good winter driver and couldn't understand what was happening until I realized it was the brakes releasing for a second, causing the car to lunge forward. I encourage everyone with this problem to report it to the NHTSB. The "flash" fix provided by the dealer does not fix this problem & I was told by the dealer that I have to live to drive with it. This is outrageous! I waited 3 years to buy my 2010 Prius & I am sick about this and I am not going away until they fix my car!
#307 of 366 Re: Prius 2010 Brake fix [mission1]--RELATED ISSUE
Nov 03, 2010 (8:43 am)
These messages have focused me on seasonal sense of dread about facing the second winter with my 2010 (in the Wash DC area, where at one point last Feb we had three feet of snow on the ground and few have decent winter driving skills). I agree the flash fix did not resolve the issue. On the other hand, I grew into getting used to it and did not take a "lunge" in a bad place like a snowy intersection. I probably need to steel myself to get back into robotically compensating for this problem.
RELATED PROBLEM--This is related only insofar as it concerns what happens when you depress the brake pedal. Every once in awhile another driver tells me my brake lights come on late. Where I can see the red glow from my own brake lights reflecting off a surface visible in my rearview mirror, I occasionally get the same feeling. No need to describe how dangerous late brake lights can be, especially with the endemic tailgating at any speed on the roads where I am. Does this sound familiar? Can it be fixed by a dealer?
#308 of 366 Re: Brakes failed to stop my 2010 prius and wreck ocurred [mission1]
Nov 03, 2010 (11:02 am)
Have you not driven a FWD vehicle on an adverse condition, slippery, roadbed previously...??
But to be fair I have had EXACTLY the same instance you describe in a '92 Jeep cherokee Limited. On a truly slippery surface the Jeeps ABS system will become so active that you literally cannot bring the vehicle to a full stop.
The conditions you describe are exactly the reason FWD vehicles are so hazardous for wintertime use. Now here you are in a vehicle with tires specifically desired for low rolling resistance....LOW TRACTION coefficient except on a reasonably tractive surface.
Next time try careful/judious use of the rear implemented e-brake, parking brake.
#309 of 366 Re: Prius 2010 Brake fix [mission1]--RELATED ISSUE [masterpanda]
Nov 03, 2010 (11:07 am)
!!...CAUTION, HAZARD, DANGER..!!
The rear brake light switch, control, is an integral, KEY component of your hybrid's braking system. If the brake lights are not coming on the very INSTANT you touch the brake pedal, even lightly, the regen/frictional braking system will not operate as designed.
#310 of 366 Unintended Sudden Braking
Dec 22, 2010 (5:44 am)
Just bought a 2010 Prius V with the Technology Package. Bought from a Ga dealer 200 miles away. On my trip home to TN, on two occasions, while traveling 70 mph, dynamic radar cruise control on, lane keep assist on, the vehicle suddenly braked. Both times I was passing a semi-tractor/trailer rig on a slight right curve. I understand how the pre-collision avoidance system could be a cause if I was on a sharp left turn. But this was on a slight right curve. I'm taking it to a dealership today. Has anyone else had this issue? I know there aren't many Priuses with the Tech Package. I'm confident that one of these tech features failed to operate as intended.
#311 of 366 Prius brake problem fix
Jan 06, 2011 (11:13 am)
I believe that bleeding the brakes can correct the Prius brake grabbing / failure problem. I believe bleeding of the brakes, flushes air of foreign material out of the “Brake Actuator” module.
I have a 2004 Prius that we bought new.
At about 90,000 miles the brakes would grab at low speed (less than 5 MPH) when backing out of the garage or coming to a stop. This was a intermittent problem which could not be reproduced at the dealer, and the dealer could find no problem with the brakes. There were no alarm light on the instrument panel.
At about 100,000 miles the car developed a second brake problem, in that at higher speeds (about 30 to 50 MPH) when braking, the brakes would suddenly fade for a second and then grab, this would repeat it self, bringing the car to a very jerky stop. There was no alarm lights, and this was not an ABS stop. The dealer could got find any problem with the brakes.
At about 112,000 miles the higher speed braking event happened twice with in a month. I took it back to the dealer and they did a 100% inspection of the brakes and could find no problem. As part of this inspection they bleed the brakes. I have now driven the car for over 3 months and greater than 1,000 miles, and have had no problems with the brakes.
#312 of 366 Re: Prius brake problem fix [bandorgan]
Jan 06, 2011 (11:26 am)
Bleeding the brakes prolly did not do any good. If there was air in the system previously, you would have noticed it when stopping. Pumping the brakes would have been required, and a "low" pedal would have been present.
#313 of 366 Re: Prius brake problem fix [bandorgan]
Jan 06, 2011 (12:39 pm)
Thanks for the info. My 2010 Prius is JUNK!!!!! I wish someone would steal it and I would never have to see the car again! Paid way too much for it, can't sell it now that it has been wrecked. Continue to feel like my car is very slow to respond if/when urgent braking is needed. The braking system on this car is unsafe.