braking in reverse

[garygid]

THE BACKUP BUG - UNEXPECTED ACCELERATION

Just yesterday, my Prius-III backed up with sudden unintended acceleration, with my foot only on the brake pedal. No, the accelerator pedal was not "stuck" or being touched in any way. The parking spot was level.

I recognized what was happening because it happened once before, just over 2 months ago, just a few days after I got the car, when I was backing out of an inclined driveway. Perhaps insignificant, but both times, I had a passenger in the passenger seat.

I suspect that some unusual element of the timing of turning the car ON, and shifting into Reverse, and possibly the internal state of the computer and the hybrid power system combine to produce this "abrupt" reverse acceleration as I am gently easing off my foot pressure on the brake pedal. Others describe this as an annoying "Abrupt Braking", and the abrupt braking effect does occur, but only in response to the much more DANGEROUS "unexpected, unintended" reverse power (acceleration), to stop the car motion. No matter how gently the brake is eased further ON to stop, the stop is "abrupt", not smooth.

Yes, in this case pressing the brake gently, just a little, stops the car, but with a big "Jerk" (the Abrupt Braking effect). Then, shifting into Neutral and then to Reverse again "resets" the software so that further backing is the normally expected gentle movement of the car.

However, the unexpected "jump" backward (due to the unexpected power and acceleration) might have caused an accident, crashing my car into anything behind it. This is DANGEROUS.

And, after the crash, who would believe me when I said, "The Prius-Backup-Bug did it, not Me!"?

Sincerely trying to help Toyota have a better Prius,
Gary ..., PhD
Prius-III + Nav, made July 2009 in factory "5"

[macdonald]

I have experienced the brake grabbing problem on more than one occasion. When it happened yesterday I was backing out of a parking space where I could not see behind me well, and had to move very slowly.

[prius4driver]

I'm so glad I found this topic! Have had my Gen III nearly 3 weeks--have under 700 miles on it. Saturday night I experienced the grab--thank goodness not as severe as many here. It had been parked on an inclined driveway at a party. It grabbed when I first used the brakes. This house is just over the crest of a hill--dangerous spot. Can back enough to then pull forward on the shoulder before going into the road, and it grabbed in forward also. Figured it was just me. So far that is the only time it has done it. It was OK at the first stop sign a couple of blocks down the road. Thanks to ALL!

[Pugsy]

I've reached the point where I know when it will happen. Every time it's happened to me it's been when I sat in the car a minute or 2 before turning it on: at the dealer, as the salesman explained some things to me; at the mall, going through a bag of items I just purchased; writing a check I'm about to mail; chatting with my passenger before I power up; eating a burger I just bought at Sonic, etc. The last few times I thought to myself, "um, I didn't turn it on right when I got in, so I'll probably experience the jerking," and sure enough, I do. Now I turn the car on right when I get in, even if I'm not expecting to drive off immediately, and I haven't experienced it since.

[garygid]

Pugsy,
I have been trying to find the timing combination that will
reproduce this problem.
I thought it happens when I drive too soon after I turn the car ON.

I will try your "sit-wait-ON" method, and maybe a
"sit-wait-ON-move-quickly" variation.

I am SURE that this is NOT related to the "gas" pedal being physically stuck down.
Thanks.

[energyandair]

Its only happened to me on one occasion.
I has stopped for a few minutes in a steep uphill driveway off a cul de sac,to drop a friend off.

When I tried to back slowly out into the cul de sac (no throttle as the driveway was very steep), the brakes would not modulate. They were either off or grabbed tight. Off was not a good option as the space was very tight and I had to turn sharply.

IIRC, I had stayed in the car but I'm not sure if I left the car in drive, put it in park or turned it off.

[egale]

I am finding this is what triggers it for me. I drive to pick my wife up at the train station. I pull in a space and turn the car off. The car then sits 5 minutes give or take before I turn the car back on. If it is going to happen, this is it. The parking lot is flat and level. I don't think an incline has anything to do with it. I think it has to do with turning the car off and turning it on too soon again.

[organist]

I have also experienced the violent locking of the brakes on my 2010 Prius. I just press the brake pedal about 3/8" and they lock so hard that the car rocks on its suspension. This happened a lot while backing out of parking spaces when the car was new. That has diminished recently, but I had my first lock-up while going forward yesterday. The car now has about 4,500 miles on it.

This has always happened while backing out or going forward out of parking spaces, never while actually driving. It's pretty erratic, so it's hard to figure out exactly what causes it. It doesn't seem to be related to how long the car has been parked. Yesterday I was sitting in the car talking to a friend before turning the car on.

My best hunch is that it happens when I put the car in gear before its system has booted completely. It's possible that I tend to start up the car more hastily if I've been sitting and talking first. Today I counted to about 25 after all of the warning lights on the display had gone off and the gasoline engine had kicked on, and had no problems. Unfortunately one day's experience doesn't mean much.

[KDC]

I had this happen to me a few days ago. Backing out of a parking place downhill, it seemed that the motor was producing more torque than normal, and I was unable to modulate the brakes, they would grab quickly when applied. After moving forward and backing again the problem went away. The car had only a little over 100 miles on it then, and only 300 miles now and has not had a problem since. I was more worried about the extra acceleration than the grabbing of the brakes; several others in this thread mentioned a greater acceleration, so maybe this is also part of the problem.

[rrolff]

Well - just adding another me too (well not me - my neighbor). Neighbor bought a 2010, and the other day we were talking about our cars - she mentioned that it acts strangely sometimes when backing up - something about the brakes. I haven't noticed it on mine though.