I just rented a '08, and it has no manual. Not that I would have' read it! I thought it might be "battery", but it doesn't seem ta change anything... See it here...
Quick answer - "Braking". It increases the drag when your foot is off the accelerator - partly by engine braking. Use it to help maintain control and relieve wear on the brake pads when going down a steep hill. Someone will come along with the complex answer shortly - but that's for anoraks and efficiency obsessives, which I suspect you're not.
Here's the complex answer: http://techno-fandom.org/~hobbit/cars/b-mode.html One-handed driving w/ narration and controlling a camborder at 100+ MPH? I'm glad I wasn't on the road near you! Also, FYI, the Prius has a software-limited top speed, so not much need to test it
"B" stands for engine Braking. You might use it like a lower gear when going downhill. I wouldn't bother. Most Prius owners never use it. I've never used it in 11 months of driving my Prius. If you're going forward, just keep in Drive.
"B" is for Bad mileage Its primary function is to make loud noise and waste gas. Funny they didn't label it "V8" Rob
Thanks for the link! The take-home message I got is to use the "B" mode when highway signs instruct truckers to use lower gear. (Gotta love all those signs on I-70 west of Denver.)
I-70 west of Denver is EXACTLY what B-mode is designed for. I was actually going to write about that stretch as an example. It's pretty fun flying down that road into Utah, but I haven't driven that one in the Prius yet. That'd be a nice 90 MPH warp-stealth glide... maybe it's time for a road-trip!
'B' works so well there!!! Hwy 119 west of boulder is another great place to use it. It's useless in Florida!
When I was young, we had a 57 chevy that had a GR shifter position which stood for Grade Retarder. Folks said it was for the noise it made when we used it.
A comment and a question on the B shift issue: 1: Coming down a long and winding mountain road in Shenandoah National Park, I used B the whole way down. Then, for a few days, every time I let up on the brake pedal, there was a squeak. Sounded like the car needed WD-40. After a week or so, it went away. What's the deal? 2: When the engine turns on and off for no reason (other than to charge the battery, I suppose) does it use gas? (This may be a really stupid question...) If so, is there a way, during hohum city driving, to force it not to do this?
1. I doubt if there's any causal relationship between a braking noise and the use of B mode. 2. Don't worry too much about it. You can make yourself familiar with the warmup stages of the Prius, which require different behaviors from the system at different times. Your best bet is to get yourself into stage 4 of the warmup cycle as early in the drive as possible. Then you can minimize engine use. The engine cycling is really never for "no reason," even though sometimes you don't want it on
The squeak was probably from extended use of the friction brakes coming down the hill. Regen and B mode can only do so much; after that it's friction. You probably polished them a bit, and they squeaked until the glaze wore off. Tom