Braking Problem

There is a vacuum system that makes the brake pedal easier to depress. This is called "power brakes" This system has developed a leak causing it to lose vacuum pressure when powered off and creating the "hard" brake pedal. It's not dangerous, maybe only a little annoying when you need to push the pedal to power on. But you actually don't need to deeply depress the brake pedal on starting, only a light touch on the pedal will activate the brake light, the thing that's needed to allow starting. You could try to have the vacuum system repaired, I guess, but as long as the vacuum returns after starting the car (an electric vacuum pump creates the pressure) then you should be able to live with it. This happens in many modern cars with electric brake vacuum systems. I have it in BMW and Ford as well.

 

That description gives the right basic idea, except that no vacuum is used in the Prius system. There is an electric pump that pushes brake fluid into a pressurized chamber, so the Prius "power brakes" are powered by (fairly high) positive pressure, not by vacuum.

The brake pump in the Prius will begin to run as soon as you open the driver's door to get in the car, if the pressure is below setpoint. You should be able to hear it as a soft, rattlesnake-like noise from under the hood, running for some number of seconds from when you open the door.

If you wait for the pump to shut off before trying to start the car, you should notice the brake pedal has its normal easy feel then.

If the pump is taking longer to shut off than it used to, it is possible that the pump itself is old and worn, or that the car's 12 volt battery is low on charge (as that is what has to power the pump, before you have started the car). When the battery is quite low, the pump will sound less like a rattlesnake and more like a dying wind-up toy.

If that's what's happening, you may see improvement by fully charging, or replacing, the 12 volt battery.

 

more likely you need a new actuator. how many miles/km on her?

 

My Prime does something similar. First thing in the morning, normal depress to start. But after parked for maybe half an hour or a little longer, strong depress (or a few pumps) to start.

Also, may consider moving thread from Prime plug-in charging to Gen 1 PiP forum.

 

Thank you for correcting my understanding of the Prius power brake booster!

 

Same idea applies to the power steering and A/C. In conventional internal combustion engine cars, the power brakes, power steering, and A/C are powered (in some form) by the gasoline engine. These are all electric in the Prius, so they function independently of the gasoline engine. I had a first generation (2001, I believe) Prius, in which the A/C was powered by belt to the gasoline engine, so the gasoline engine had to be run get get any cooling, like when stuck at a traffic light. Real annoying. Starting with the second generation (2003), the A/C is electrically powered by the hybrid battery.