You have R N D and B. What is the B for?

It is how you make your Prius use its engine to slow the car on grades, like steep downhills. This is used because keeping your foot on the brake to slow the car on long downgrades can burn out the brakes. That could lead to other difficulties you would be better to avoid, hence the "B" position on the selector for the transmission.

 

But you should know that when using the "B" position the car didn't run any more in the 'ECO' mode.
What New_Yorker said is right.

 

I think it strands for Engine Brake. The word Engine is silence. It slows the Prius down by the engine creating drag by pumping air in and out through a small intake opening.

Since it is designed to waste energy, there is no way to use it efficiently.

 

The "B" mode is a an engine braking mode. It is designed, as mentioned here for longer downhill grades (driving out of the mountains) where the vehicle may otherwise gain speed from it's own momentum.

What it does vehicle wise is allow the engine to spin without burning fuel, to add a little additional resistance to the wheels, in effect preventing it from speeding up. I would be concerned that doing this too much could cause engine issues.

The thing to keep in mind with the "B" mode is that while you should not keep it there (in "B"' mode) too long, the only time it functions is when you are off the accelerator. This means that if you kept it in "B", and drove that way for a while, you would not affect your performance the same way that you would in a normal car, as the engine is not in a different gear. Additionally, when you press the gas pedal, the reaction from the vehicle would be identical as when you accelerate in "D" mode. Only when the foot is off the gas, does the braking kick in.

I've driven that way a for a while one day when I 'accidentally' forgot to disengage"B" mode. After speaking with my dealer, they confirmed that it does not damage anything, but could cause me to burn slightly more fuel, as i will not get as much 'glide' in my pulse and glide driving...

 

Near you, where B is appropriate, coming down:

[ame="http://en.wikipedia.org/wiki/Palomar_Observatory"]Palomar Observatory - Wikipedia, the free encyclopedia[/ame]
[ame="http://en.wikipedia.org/wiki/Cajon_Pass"]Cajon Pass - Wikipedia, the free encyclopedia[/ame]
[ame="http://en.wikipedia.org/wiki/Tejon_Pass"]Tejon Pass - Wikipedia, the free encyclopedia[/ame]
[ame="http://en.wikipedia.org/wiki/Donner_Pass"]Donner Pass - Wikipedia, the free encyclopedia[/ame]

 

You didn't mention [ame="http://en.wikipedia.org/wiki/Monitor_Pass"]Monitor Pass[/ame]. You need it there too. :madgrin:

[ame="http://www.vimeo.com/1708849"]Monitor Pass on Vimeo[/ame]

Hobbit has a rather in depth explanation here:

http://techno-fandom.org/~hobbit/cars/b-mode.html

 

Dogfriend I did a walk of 2500 miles in 1981 along the PCT. I listed passes I remembered climbing down into near Southern CA, plus Donner as it is THE major pass in central CA.

We sure climbed down into a lot of passes in the Sierra.
http://www.pcta.org/images/media/pct_map_high.jpg

 

Yep, PCT goes a little to the west of Monitor Pass. There are a lot of steep hills in the Sierra. Here is another spot to use B mode: