Anyone else notice this: whenever my Prius has been at rest for a while, such as sitting overnight, and I come out in the morning for my drive to work, as soon as I grab the handle and the door unlocks there is a distinct sound like a motor/servo/positioner under the bonnet that runs for about 3 to 4 seconds. I am curious as to what this is. It's 100% consistent, so it appears the car is prepping something in anticipation of starting the hybrid system - part of the "pre-flight prep" procedure perhaps? Going on my first month and 1200 miles in my new Prius Model Four w/Advanced Solar Roof package, Sea Glass exterior / dark gray interior, and loving it! Calculated average so far is a tad over 54 mpg!
Brake booster making sure you have enough pressure in the brakes since the braking system is different from a regular ICE car since the engine isn't always running to create vacuum for the brakes. I'm probably vaguely touching the surface. I know in the Gen II they have a coolant reservoir/thermos but they removed that for the Gen III
sdtundra, thanks for the insight, even my PiP does make a similar noise in the morning, but i have not paid attention that much. if its related to brake, your explanation makes sense.
Well, it's the brake booster pump priming the accumulator so you have extra hydraulic energy for braking. I say "extra" because there is enough without running the pump to stop several times with hard braking. These engineers -are- Japanese after all. It wouldn't do to tempt fate!
