Hello: I have a customer that says her 2010 Prius accelerates when she is lightly braking under normal conditions on a flat surface. This has apparently happened to her a couple of times while driving in town and then coming up to a stop with light braking. Today I recieved an email from her stating "the car jolted forward" when they were coming up to an intersection and braking lightly. Back in February this year this was her complaint "CUSTOMER REPORTS WHEN VEHICLE IS PARKED ON A DOWNHILL SLOPE - START THE VEHICLE AND PUT INTO DRIVE THE VEHICLE LURCHES FORWARD ON ITS OWN ONY OCCURS ON DOWNSLOPE" at this time we did what we call a health check on the car and found nothing abnormal and did the reburn as per Campaign 21(A0B US) at 11704kms. she then said in April at 15816kms that she had the unintended acceleration when coming to a stop. At this time we did what is called for by Toyota Canada which is a check of any codes,floor mats etc and found nothing. She then came in again in May at 18126kms and complained that she was losing braking power when braking around town-on smooth roads and in town driving and again we checked for any codes and inspected brakes to again find nothing. She then brought the Prius in again in June at 18744kms for the complaint about the brakes again-also that her shifter would not go into reverse or drive at times which we again scanned for any codes and found nothing. Which now leads us to the email I recieved this morning regarding the car accelerating when braking. I personally think that they do not want the car but as a manager I am taking their complaints very serious. We are metting with them next week to discuss the possibility of giving her my demo which is a Venza and for me to drive their Prius for a least a month. I am sorry for the long post but I am getting to the end of my wick and has anyone come across any of theses complaints. Thanks for listening and I look forward to any comments or suggestions.
Jamkat and welcome to PriusChat! :welcome: Since I'm not there, I'm going to speculate. I'm also not a technician and tend to talk in broad terms. Others will fill in the gaps. When the Prius transitions from regenerative braking to friction braking, there is a brief moment in which there seemingly is no braking. By brief, I'm talking about 0.8 seconds. There is nothing wrong. However, there is a huge difference between momentarily non-braking and lurching forward. The sensation experienced when deceleration unexpectedly stops feels like a lunge even though there is no lunge. The driver is expecting to slow and instead they maintain the same speed. To the mind, that feels like a lunge and those 0.8 seconds feels like a few seconds. My advice is to ride with her or - better yet - drive the car with her as a passenger. I'm guessing - again, remotely - that you will experience the braking transition for yourself.
Sounds like the traction control is kicking in. Rather than acceleration, what is being experienced is that braking is momentarily interrupted until traction is regained. I don't like it either, but it is normal behavior when the tires slip on gravel or a pothole. There are a number of treads discussing this.
This just occured to me. It won't solve the customer's problem but will shed some light on the lunging sensation. In a parking lot or other safe area, get a car up to a about 50 KPH. Then start braking. When you're at about 25 KPH, shift into neutral. It would be more fun with a passenger and if the passenger doesn't expect it. What you'll feel is the free-wheeling of the car. Since you're in neutral, you know as a fact that you can not possibly be applying acceleration to the vehicle. But as soon as the braking cuts out, you will feel as though you are lunging forward. Close observation of the speedometer will show you maintaining speed (assuming you're not going downhill).
I agree with this response, happens every time at low speed coasting to a stop and suddenly going over rough ground (railroad tracks), it could be mistaken for sudden acceleration(because your speed is not decreasing)
The "acceleration" while braking is not acceleration; it's a momentary drop in braking. The human mind perceives the lowered braking as forward acceleration. The short reduction in braking occurs when traction control kicks in, which forces the car to transition from regenerative to friction braking. This is normal and happens with all Prius when traction is lost during braking. As for lurching forward while stopped, unlike most cars, a Prius will start and stop its engine at random times. The torque from the engine will cause the Prius to try and move forward if you don't have your foot on the brake. This is also normal and simply an artifact of having the engine start and stop. Even if you don't have your foot on the brakes, it won't move very far. The parking pawl will keep it from moving while in park, but it will rock a few inches. Tom
In addition to TonyPSchaefer's suggestion to ride along, I have an accelerometer I can loan you: Send me a PM with your business address. We used the Gulf Coast Data Concepts accelerometer to quantify the brake pause: Later, we used the same accelerometer to demonstrate the problem is gone: If you have an iPhone or iPad, there are less precise accelerometer software applications that can record some data. Although I was able to extract events, they are rubbish for long-term measurements, too much drift. You didn't mention SSC-A0B. Has it been applied? Has anyone verified it is in the car? We had one report of a car that upon return to the dealer they discovered someone had failed to apply SSC-A0B. BTW, a ride-along is unlikely to reproduce the problem at will. It is an intermittent problem. HOW REPRODUCE Requires 'slippery' street, light rain or drizzle damp. Speed less than 19 mph (30 km/h) at bump or pot hole Significant bump or pot hole, 4" (10 cm.) Light braking approaching the bump or pot hole If the streets are dry, no luck. If the speed is above 19 mph, no luck. If the braking is not light, no luck. If the bump or pot hole is too small, no luck. It is the combination needed to ensure replication. One last thing, I collect photos of sites that replicate the problem. Just give me enough information for a Google StreetView or take digital camera photos of the location. From my collection: http://hiwaay.net/~bzwilson/prius/Prius_bump_010.jpg http://hiwaay.net/~bzwilson/prius/Prius_bump_020.jpg http://hiwaay.net/~bzwilson/prius/Prius_bump_030.jpg http://hiwaay.net/~bzwilson/prius/Prius_bump_040.jpg http://hiwaay.net/~bzwilson/prius/Prius_bump_050.jpg http://hiwaay.net/~bzwilson/prius/Prius_bump_060.jpg http://hiwaay.net/~bzwilson/prius/Prius_bump_070.jpg http://hiwaay.net/~bzwilson/prius/Prius_bump_080.jpg http://hiwaay.net/~bzwilson/prius/Prius_bump_090.jpg http://hiwaay.net/~bzwilson/prius/Prius_bump_100.jpg http://hiwaay.net/~bzwilson/prius/Prius_bump_110.jpg http://hiwaay.net/~bzwilson/prius/Prius_bump_120.jpg http://hiwaay.net/~bzwilson/prius/Prius_bump_130.jpg http://hiwaay.net/~bzwilson/prius/Prius_bump_140.jpg http://hiwaay.net/~bzwilson/prius/Prius_bump_150.jpg http://hiwaay.net/~bzwilson/prius/Prius_bump_160.jpg http://hiwaay.net/~bzwilson/prius/Prius_bump_170.jpg http://hiwaay.net/~bzwilson/prius/Prius_bump_180.jpg http://hiwaay.net/~bzwilson/prius/Prius_bump_190.jpg http://hiwaay.net/~bzwilson/prius/Prius_bump_200.jpg http://hiwaay.net/~bzwilson/prius/Prius_bump_210.jpg http://hiwaay.net/~bzwilson/prius/Prius_bump_220.jpg http://hiwaay.net/~bzwilson/prius/Prius_bump_240.jpg I remain interested because it is not uncommon to find a second, less frequent, intermittent problem associated with the first. We know SSC-A0B fixes a problem so my mind is still open the possibility of a second. Bob Wilson
Bob, That's a cute little logging accelerometer package. Is it this one? GCDC X6-1A Usb-Accelerometer 3-axis Data Recorder Also that was a nicely done experiment. I hadn't seen it before. Thanks!
Yes, they have two models. One requires a AA battery and the other comes with a small LiON cell. Bob Wilson
It appear the person does drive a lot The only unintended acceleration when coming to a stop happen to me about 3 weeks ago on a very rough road under construction, there was a lot of loose stone on the road, we have not had the braking reprogramed But beside that I have had no problems The mind does funny things once a person does not like something and this is probably the problem
I have felt this condition when applying the brakes after the cruise control is activated. It is very slight but it is there.
This thread needs a more specific title! I almost missed it... I was going to post about this problem, which I'm also experiencing. I have plenty of experience with cruise control in cars, but the Prius's reaction to braking in Cruise is a little unnerving. When I apply the brakes while in Cruise mode, the car does feel like it surges forward a bit, briefly. My theory is that the cruise isn't cutting out when the pedal reaches the Regen portion of its travel - it's waiting until the brakes are actually applied to switch off. It may be that the brakes are hesitating before they engage, but it feels more like the Cruise Control isn't disengaging quickly enough...
It disengages when your brake light switch is activated, so take a look at when the lights come on versus your pedal movement. It could be you need to adjust (or have the dealer adjust) the switch which contacts the pedal arm. My lights come on very early in pedal movement (as delivered), and I've noticed nothing unusual about the Cruise.
