Just Bought an 09 Prius - need help on getting to know its sounds

Are both noises the same?

The second is definitely not a fault, that's just the braking system recharging or some such and is perfectly normal. Happens on both of ours all the the time.

LG-H815 ?

 

The sounds you describe are normal. You aren't getting any warning lights on the dashboard, or check engine light? If not, and brake performance doesn't seem to be affected, then don't worry about it.

 

The sound you are describing is considered normal. It is what you suspect, the actuator for the brakes. The Prius braking system is very complex and unlike traditional brakes on most vehicles. I have driven more than one Gen II Prius (2009) and heard the same noise. Other's have commented on it and have been told it is normal on this board.

The sound you are describing is normal. There is a thermos bottle that stores hot coolant and recirculates it into the ICE upon start up to aid in getting the ICE up to normal operating temp quickly. Sometimes that pump can get pretty noisy, especially during the winter. The thermos is hidden in front of the wheel well on the drivers side.

Best of luck to you,
Ron (dorunron)

 

You've already seen the answers, but I know sometimes an answer is more satisfying if there's an explanation with it, so:

Most cars have power assisted brakes these days. The conventional way to do that is to have a big "booster" between your brake pedal and the master cylinder. In most cars it looks like a big round tub that the master cylinder bolts onto, and it has a hose leading to the engine. There's a big flexible diaphragm inside that tub, and vacuum created by the engine intake is on one side of it, and when you step on the brake, atmospheric pressure behind the diaphragm shoves in the same direction, and adds to the force you put on the pedal.

A Prius can't work that way at all, because the engine isn't always running while you drive. So it needs a different way to boost your braking effort. What it does involves a metal can called the "accumulator" containing a bellows and a high-pressure gas, and an electric pump. The pump forces brake fluid into the can, against the gas bellows, until the can is filled with fluid at a couple thousand PSI of pressure. When you step on the brake, some of that pressurized brake fluid enters the master cylinder too and adds to the force you put on the pedal. (The antilock brake system can also make use of that pressurized fluid by opening valves under computer control.) When you back off the brake, the fluid travels back to the reservoir, so with every use of the brakes, some of the pressure in the accumulator is used up. Whenever the pressure goes below a minimum, the electric pump runs again and pumps it back up to the max. That's the sound you're hearing.

Notice I called this thing where the pressurized fluid is kept the accumulator. There is also a part in your car that's called the brake actuator (it's the box with the valves controlled by the ABS computer) and they're easy to confuse in the Gen 2 because they're in the same assembly and you can't buy them separately any more (from Toyota at least), but still, when you hear that sound, it's the accumulator pump you're hearing.

If the computer ever detects that pump isn't working right, it will light up BRAKE and ABS lights on your dash and sound a high-pitched beep. Pay attention if that happens, because it means you might (or might not) have a few stops left you can make with boost power (on whatever pressure is left in the accumulator), but after that you'll be braking on foot power alone and it will get a lot harder to stop the car.

-Chap

 

Thanks. I've been waiting for this. Great write up.