Brake pedal won't depress

shouldn't be any different from any other car, no matter what you do. maybe something loose down there. get it back to the dealer for inspection.
to start the car, the brake interlock switch must be activated. this happens when you apply the brake before pushing the go button. if it is not, you enter accessory mode only.
sometimes, the switch needs adjustment, but if the pedal isn't moving, you have another problem.

 

The 'gone to sleep' idea makes me wonder if the accumulator for the power assist (or 'stroke simulator') lost its pressure, and failed to re-trigger the pressure pump. It that case, it still should operate in old-fashioned manual mode, without the power assist. This is a federal requirement for passenger cars, as a failsafe for power assist failure.

If you put your full body weight (or at least 113 pounds-force, or metric 500 Newtons) into the brake pedal, does the brake still work in that old fashioned manual mode? If it doesn't, it is an automatic safety failure that should be reported to NHTSA: File a Vehicle Safety Complaint | Safercar.gov | NHTSA

Most importantly, if-when you feel a stiff brake pedal, don't automatically give up and assume that it doesn't work. Train yourself to revert to the old days of non-power brakes, and really stomp on the pedal. Use your full body weight.

 

My bare-bones '16 liftback does that too. So I open the door, get out, close the door, walk around the car, CUSS, throw something, re-open the door, get back in, close the door, and then the brake pedal depresses fine and I can power up that Disneyland car. I got it down to a science!

These cars are full of all kinds of weird glitches, flaws, and annoyances. Especially the Prime it seems. Toyota quality has fallen off a cliff! (HOW LONG have they been building the Prius??? And it's getting worse.) We got two choices: sell it; or put up with all these freakin' strange oddities and Just Drive It.

I know one thing for sure... I'll never buy another one. After only 24 months, I'm already tired of playing in Disneyland.

 

i'm on my third, never had it happen, take it to the dealer.

 

When the boost pressure is lost, the pedal does feel pretty much rock hard. In fact, that's a procedure in the manual for making sure the pressure is all relieved before checking fluid level or doing work (except on Gen 2, which works differently): disable the pump, then press the pedal some 20 or 30 times until—BAM—you know the boost pressure is used up, there's no mistaking it.

In truth, you can still press it in that state and make the car stop; it just feels like you have to really stand on it.

If that much fluid is escaping the accumulator between the time you open the door and the time you go to press the pedal, there would have to be an internal leak, not small. It's more typical for the pressure to mostly hold overnight (with the pump only running a few seconds in the morning to top off). Ought to be tracked down and fixed, not Just Driven.

-Chap

 

It has happened on my Gen 4 several times, mostly when it has been shut off (for refueling, for example) for only a short time. I can still power up just putting pressure on the brake pedal even though it does not seem to move, and after starting the normal boosted brake pedal feel returns immediately. Now, I'd worry about it if the boosted brake pedal did not return after powering up.

 

interesting, i wonder if this is a new toyota 'feature and benefit'?

 

No such problem in my Prime. This sounds like a warranty item.

 

No such issue on my 2017. I agree it should be a warranty issue and may be a safety issue.

 

But what are the chances that the OP takes it to the dealer and they will not be able to replicate the problem?

 

100%

 

It sounds like a new problem. I'd recommend taking it in to at least get it on a service report even if the local service center isn't able to fix it on the first attempt. In the meanwhile, I'll see if I (any helpers?) can replicate the problem.

This is typically called an intermittent which is difficult to diagnose until we find a way to replicate it at will.

Additional details:

1. Parked on level?
2. Use parking brake?
3. Climate conditions, temperature, rain/wet?
4. How long off?

Bob Wilson

 

I vote for "gone to sleep" idea. I believe it is just a power-assist thing. No problem.

It happened to me once a while, but I never paid too much attention to it because I could normally turn on without further depression and brake was normal once I started driving.

You know brake is harder in a normal car before turning on the ICE. Prime experience should be a similar thing and same with my G2 prius, as I recall, although Prime brake is much harder when it happens.

It happened this morning and as I read your post, I realized I forgot something to do on my phone when I got in, and spent a few minutes without turning on the power!

So I tested after work this evening. I got in, did nothing for 3+ minutes. And voila! It reproduced.
BTW, it didn't happen when I moved my car to the charge station in the parking lot in the mid afternoon.

Hope other folks will reproduce and convince you.

 

Similar, but not the same, because your assist in a normal car comes from atmospheric air pressure against vacuum created by the running engine. That doesn't stay stored very long while the engine is off.

The assist in a Prius comes from a pressure vessel pumped up with brake fluid to very high pressure, and most of us (with older generation Prii, anyway) are used to that pressure holding up for long periods, even pretty well overnight. (The pump will run briefly to top it off again, but nowhere near like pumping up from nothing.)

So this is odd. I guess I can't rule out that Prime (or Gen 4 generally) added a solenoid that just seals off the pressure source when 'asleep' ... if they did, probably the New Car Features manual has something to say about it.

If that isn't it, then it's still weird to be able to lose assist so quickly.

-Chap

 

This same situation has occurred at least half a dozen times with my Prime Advanced. It has not failed to start, nor affected braking performance after starting or moving. I'm not at the point where I'll bring it in for this, but now that I've read the OP's report, I might consider calling this an oddity and short of a defect.

 

If that isn't it, then it's still weird to be able to lose assist so quickly.

-Chap[/QUOTE]

I would assume some kind of lock system rather than losing its pressure. I anyway hear the buzz sound right after turning on, though.

Hope other guys will test (no wait vs 3+ min wait) to confirm.

 

Hmm, there are two things you could mean by "the buzz sound" right there ....

One could just be the normal whirring sound of the pump when it runs. That's normal (as long as it doesn't happen too often or last too long when it happens).

The other is the actual buzzer that Toyota builds into the system to sound a warning when the pressure has dropped too low. Hearing that would be a sure sign of a problem. (It's called a "buzzer", but the type they've usually used is more of a high-pitched steady beeeep.)

Here's hoping you just meant the pump sound.

"Some kind of lock system" could be a possibility, which, again, I'd expect to find discussed in the New Car Features book, which has always described the braking system in detail for each model, with special attention paid to whatever features are new or different from the previous. I'm not quite curious enough to make it the question that spurs me to another $15 weekend of techinfo browsing. But ISTR maybe Bob Wilson downloaded a lot of the Gen 4 NCF. Maybe he'll have downloaded a section that covers this.

-Chap