What is the B on the shift column ?

Engine braking. Use it for descending long and steep roads, like those you find in the mountains.

Tom

 

A normal Automatic is PRNDL, some one at Toyota was too honest to call theirs L because there are no Lower gears, just engine braking, so they called it B.

If you went down a long steep hill in a Prius, the HV Battery would fill part way down and you would have no regenerative brakes, just friction brakes. Toyota added engine braking (wasting energy by using the engine as an air pump, the harder you hit the brakes the faster and louder the engine gets) so the disc brakes do not over heat and boil the brake fluid. (that would be BAD)

The B mode allows you to plan ahead and start engine braking even before you run out of regenerative braking, so your friction brakes stay cool.

My 'favorite' down hill: http://www.oregon.gov/ODOT/MCT/docs/EmigrantHill.pdf?ga=t

You may use B anytime, but above about 20 MPH you are just wasting energy and lowering gas mileage. Cruise Control does not work in B

 

Just stressing to the OP that if you do go down a long/steep hill in B mode (or even in Drive) the engine will start to rev and sometimes rev loudly. It is normal and not a fault. Also, when you reach the bottom of the hill and stop at a traffic light, the engine might carry on revving away for a short time. This is also normal.

Your HV battery may be virtually full at the bottom of the hill and the car will do weird stuff like accelerate quickly and reach higher speeds than normal in electric only (not EV mode), but will quickly return to normal when the HV battery starts to lose charge.

My rule of thumb is that everything the car does is normal unless it flashes a warning or illuminates a warning light. But feel free to ask away with any questions or queries you have - that's what the forum's for.

 

Normally, the Prius does Not engage engine braking. It uses regen and friction brakes only. When you shift into "B," you are telling the car to engage engine braking in addition to regen.

 

so when I hit these decants if I can keep the car in regen without maxing it out to where frictions brakes are kicking in, then I don't need the B, but if I'm still accelerating and masking out the regen, then shift to B?

 

Yes. It comes down to anticipation. If you are reasonably sure that you can descend the hill without filling the HV battery to the high limit, then stay in D. If, on the other hand, you know that your battery will hit the limit before the bottom of the hill, shift to B. This will bleed-off excess energy and forestall the need for friction braking.

Tom

 

FWIW, I think it was close to a year back when I last put our Prius in B. Save it for really long and protracted downhills.