braking in reverse

The ICE starting does not affect the brakes, but it does affect the ability to move backward. All reverse thrust comes from MG2. When the ICE runs, part of its torque goes to MG1 and part goes mechanically to the drive train. The ratio is fixed. This means that when the ICE is running, MG2 has to overcome the mechanical torque from the ICE to move the car backward, making it harder to back up.

Tom

 

I am glad to hear I am not the only one with this experience. Happened only once so far, but it really puzzled me. Living in San Francisco, I do have to occasionally use "hill-assist" braking to prevent sliding back at full stop on a hill. The increasing resistance on the brake pedal as this braking-grabbing was happening, feels like it "hill-assist" was accidentally triggered somehow. Just speculation. Recalling from the incident, drive forward a little and then reverse again, solved it quickly. I had no answer when the wife asked what had just happened? lol. Hopefully Toyota can find a quick fix before our 1st scheduled tuneup.

 

This has happened to me numerous times. I've mainly noticed it when starting up and backing out of a sloped driveway and the engine has NOT kicked in. It is very annoying. I will try putting in park and pumping the brake the next time it happens. It could also be that I had been in EV mode when I pulled INTO the driveway when I last drove the car. I turn off EV when I park it, but I wonder if that could have something to do with it too.

 

Happened to me too. Three times in reverse, once going forward. Very annoying. I'm debating taking it in for service now or waiting for the first oil change.

 

Just to add my data point... It happened to me for the first time today while backing up. Dry conditions, 75 degrees, slight downward slope (10-15 degrees), car parked for one hour after having been driven for about half an hour (and after having been turned off without my first depressing the parking button), about 800 miles on the odometer. I had my foot on the brakes while starting the car and putting it into reverse. Probably only waited a few seconds between the time I started the car and put it into reverse. Brakes grabbed a couple of times before I shifted into drive. Brakes were fine after that.

 

My braking problem is when in forward motion and just barely moving. While waiting for a stoplight and I allow the car to drift forward a few feet and then gently apply the brake the brakes appear to lock up and jerk the car to a stop. This has also happened several times in parking lots while following other cars without using any throttle. Never experienced that with my 04,2G Prius. I have always had pride in my ability stop the airplane at the gate with passengers never sensing the loss of motion. My highly educated toe has been unable to accomplish this in the situations mentioned above. I find this unacceptable and will return to it the dealer.

2010 3G, II, 2500 miles, 54 mpg city, 58 mpg highway, best trip 62.7. I think this car is a huge improvement over the 2G. My only complaint is losing Smart Entry on the pax and rear hatch doors as I did not know driver's door only was a limit on the II.

 

It happened again yesterday, backing out of the garage, which is a level surface. As soon as it happened, I thought back to when I pressed the power (on) button with my foot on the brake, and I think the brake pedal sunk further to the floor than usual. The problem is I was trying to remember the pedal behavior 5 seconds before and I wasn't paying close attention as I wasn't expecting the problem. I just got in the car to go as usual. I believe the ICE also started around the time of the reverse brake grabbing. It could have been before or after. Again, when it happened, I was caught off guard and didn't pay close attention to everything going on prior to it occurring. I'll have to try to watch this more closely. Oh yes, for the first time, I put it in park and then back in reverse, and the problem was gone.

 

Does any of this problem, (Since I have yet to experience it and have not in 5 weeks of ownership) come from how hard someone is stepping on the brake prior to going into reverse, which may somehow kick in the "Hill Assist functionality" when trying to back up?? If I should experience it, trust me I will post it as well. I just have not had it happen yet.

 

Wondering that, myself--is the pedal being pushed quite a way down before the actuator pump finishes it's pumping when you open the door? I tend to not apply the brake at all until the pump completes its cycle, then just lightly. Never had the problem, either.

 

In a word... NO! Like I said before, if a bug landed on the pedal it would lock the tires up. Not being rude here but when it happens to you, you will know and you will be stumped just like the rest of us.

 

Thats not a bad idea, however when it happened to me, we had just finished about a 30 mile road trip, parked in a lot for about 15 min (with the car "on") and then backed out (no slope) and whamo.

 

Had it happen again today but this was the first time it happened going forward, and just like when it happens in reverse, the brake pedal sinks further to the floor than usual when I press the Power button. I let off the brake partially repeatedly and it kept doing it. I stayed in Drive and let off the brake completely and then it was gone. We need to somehow narrow down the conditions under which it happens. I'll have to watch for the problem in relation to the actuator pump doing its thing.

 

That's what I did to stop the problem.

 

Happened to me this afternoon. Backing out of the driveway, downhill, in Neutral, as I go N and drift a bit before choosing R at a very low speed (habit from past vehicles to keep the tranny from kicking into R and pushing me down the hill). I use the left foot on the brake and after trying to feather it a couple of times, unsuccessfully, I held the brake and sensed that it was much closer to the floor than usual. I stayed on the brake, shifted to D, pressed the throttle and eased off the brake to let the engine/motor hold it on the hill. I tested the brake and it seemed to come back up and stay in the normal depth. I then braked and shifted back to N and drifted out as usual with gradual braking. I will definitely do more troubleshooting next time.

 

It's happened a couple more times and I may be noticing a pattern. If after powering up and shifting into reverse, I let off the brake completely to start rolling and then use the brake to control speed, it does not occur. It only seems to occur when I let off the brake partially as I begin to back up, but it doesn't occur every time I let off partially. I still notice that the brake pedal sinks lower I power up prior to it occurring. I'm starting to feel like I can predict when it will happen based on the brake pedal feedback when I power up.

 

Happened to me again today. Like DetPrius I think there is a pattern evolving. In the parking lot I shutdown and then powered to Accessory mode. About 10 minutes later my wife came back and I pressed the brake and powered up. I partially let off the brake and started to back up and pressed down. The brake pedal got hard like it bottomed out and they grabbed. I pumped the pedal a couple of times quickly and all was fine. I almost felt like air in the brake lines. Or perhaps the pump hadn't finshed pumping up. Very odd.

 

It happened to me yesterday at the mall, going forward this time. I can tell now when it's going to happen by the feel of the brake. It feels hard to the touch. I think I just pumped the brake and it cleared up.

 

Spiderman and Pugsy are describing my experience in that you can feel it is going to happen. Only partially letting up on the brake after going to "gear" seems to be key to this for me. I am always able to get rid of it by completely releasing the brake and reapplying and then it's fine. One of these days I'm going to have to start trying to recreate the problem.

 

I now have over 13,500 miles on my car, will say that I have not had this happen to me once in the last 10,000 miles. Does anyone that has put significant miles on their 2010 still have this issue? Or is it something that seems to go away with time (and could be reintroduced when I eventually get a brake job?)

For those of you who have experienced this issue in forward, does it only seem to happen when starting up, taking off, or also once you have been driving? If it continues, has it even happened at a high speed?

 

Recently I had it happen for the first time driving forward. I have had it happen twice before in reverse.
Drove out of a car park and slightly applied the brakes as I crossed the footpath. The pedal felt tight so I was not surprised when the brakes came on harder than required.
I immediately took my foot off the pedal and drove about 150 yards to a roundabout. Applied the brakes again to slow down and the same thing happened.
When I was free of traffic (about 200 yds further on) I applied the brakes several times and the problem went away. My speed would not have exceded 20km/h.
I have over 7000km on my Gen 3 Prius.