Sudden Acceleration - It Happened To Us Today

Are you saying you and the wife are driving with no floor mat on the driver's side?

If not too much trouble, could you take and upload a quick photo of the gas pedal / brake area to show what repair work the dealer did a couple months ago?

I'll go first ... No chance for interference below ...





That said, I've had no unintended acceleration of any kind and if there was a hint of unintended / uncontrolled acceleration, I'd be on it immediately.

 

How long did it happen? Was it for a fraction of second or so? Was there any pothole on the turn where she was braking? Any manhole cover there?

In Prius when you are braking lightly (regenerative braking), it is a fairly common experience to feel a momentary surge if you hit a pothole or go over a manhole cover.

I have experienced it multiple times. It is quite possible something similar may have happened. It is unnerving first few times you experience it for sure.

 

My owner's manual p.492 states ...

'If you believe that your vehicle has a defect which could cause a crash or could cause injury or death, you should immediately inform the NHTSA in addition to notifying TMS ...'

 

she was approaching a red light and did not come to a complete stop before proceeding? does she drive with both feet?

 

He did state his wife was thrown back into her seat and road was clean and dry, so that seems to rule out any minor surge going over a manhole cover. But, I've never experienced it so don't really know.

 

in all due seriousness, even from a dead stop, if i stomp the throttle, i dont think the prius would accelerate anywhere near to hurt my neck.

any type of pothole would cause de-celleration, not acceleration.

I'm giving you 100% of the benefit that you're NOT a troll. Keep us posted on this. Hope your wife is well.

 

This was not sudden acceleration, but sudden loss of braking. What you describe is a classic case of traction control kicking in during braking. Normal braking with a Prius is done regeneratively, which means only the front drive wheels are slowing the car. If one of them slips over a bump or rough pavement, the traction control system detects the loss of traction and switches to ABS friction braking. The transition induces a short dropout in braking, which to untrained human senses feels like acceleration. It's really a momentary reduction is deceleration, but to your wife it would feel like the car lurched ahead.

People anticipate actions and reactions. When you press the brake, you expect to feel deceleration forces, and you compensate by pushing backward against the expected forces. When those forces suddenly vanish, you end up throwing yourself against the back of the seat, which is what your wife did.

What you describe is normal for a Prius. It will happen when you brake over an uneven surface. Pressing harder will cause the brakes to work as expected. Better tires will help, but it will still happen if the tires lose traction during braking.

If you want to read more about this, search for terms such as "brake dropout".

Tom

 

when braking with constant pressure at low speed (> 8mph) and there is wheel spin, what the OP described will happen. The symptom is - light to moderate braking over uneven terrain or slippery surface (manhole cover, broken asphalt, etc), if wheel spin occurs, traction control light will flash, braking power reduces (leading driver to think it is acceleration) for about 1 second or less.

My 07 does this over the same right turn about half of the time on the way to work, depending on whether or not there is wheel spin. I can recreate it at will over that turn, or other similar conditions.

the first time it happened, the lurch forward (reduced braking) caught my brain by surprise as I expected the car to continually slow down. Since then I plan ahead to compensate for this symptom.

I suspect it is a bug in the software.

 

MY PRIUS HAS NEVER HAD THE POWER TO EVER LURCH! Would be nice to have that power at times though!

 

I think Ive heard this story before. Oh yeah A DOZEN TIMES. NEXT.

 

A few questions for your consideration:

- How many miles on the odometer?
- Are the tires original equipment?
- How much tread depth remains on the front tires?

I would be inclined to agree with the other posters that it sounds like a front tire momentarily lost traction. This caused the amber skidding car icon to appear. The loss of traction also caused the braking system to switch from regen braking to friction braking, which takes a brief moment and provides the illusion that the car is accelerating (vs. a momentary pause in deceleration.)

In any event, your wife did the right thing by pressing harder on the brake pedal.

I'd suggest that you see if you can replicate the incident by driving over bumpy pavement, a manhole cover, or other low-traction surface while braking. Turning while braking provides an additional challenge to the front tires, and they are more likely to slip then.

Especially if your tires are original equipment, or if the tread depth is less than 5/32", I would say that your car will handle much better if you invest in a set of decent tires (not Goodyear Integrity.) Good luck.

 

Ironic that this ad appeared next to cthindi's post in my display:




Pat, you asked if anyone else had a similar experience. Here's a recent thread, but involved a 2010 Prius:

YIKES: Experienced unexplained acceleration, already had brakes reprogrammed - PriusChat Forums

2007's aren't subject to the 2010 Prius recall to flash the software for braking. But it's interesting that your scenario sounds like same thing 2010's were having: While braking-- ABS tries to engage (traction light would come on)-- "lurch forward" felt while Prius switches from regen to friction brakes-- keep mashing the brake pedal and the brakes grab again.

 

It seems that some low rolling resistance tires would be more susceptible to loss of traction, because they are of harder compound, right?

I wonder if Bridgestone Ecopias are better green tires than Integrity's since they ship on '10 Prius'.

 

I have the Ecopia EP100 tires on my 2004 and with ~5K miles so far, they have been great. However I haven't needed to drive in heavy rain since installing those tires. Also, they are summer tires, not all-season; so they are definitely unsuitable for snow driving.

 

Did she also hear the engine rev loudly? I don't think the prius can generate the power for that type of acceleration without the petrol engine coming on and revving fairly substantially.

In the current situation I think Toyota is very keen to investigate any unintended acceleration issues. I would have thought they'd take it very seriously.

 

This post is excellent and really should put the ops concerns to rest. Wouldn't it be nice if the dealership was astute enough to reply like this? My experience with Toyota maintenance people is that they don't know their products.

 

I hate potholes.

 

I have never experienced UA of the kind that OP describes, and I think I know why: I do not brake going around corners. The motivation stems from wanting MPG, but in addition to earlier suggestion to wear tyres with good traction, this is the other practical piece of driving advice to avoid the unexpected traction control kicking in.

By the way, I don't brake much going *into* corners either; I let the car bleed off speed by taking my foot off the fuel pedal enough ahead of time to reach the speed I want to turn the corner.

 

It is illegal and very dangerous not to stop at the red light before making the turn. Plus it is a sharp turn at a very busy intersection as the OP wrote. She may be lucky not having accidents in 25 years but she does not seem like a safe driver at all. I would encourage her to go through a driver safety class ASAP. Drive safely.