B gear

Check your parking brake to make sure it is released.

'B' gear should cause no physical damage or burning smell, only a slightly reduced MPG in city conditions. For flat highway conditions where you never completely release the gas pedal, it may not even hurt MPG by any noticeable amount.

But in the absence of long downhill grades that would fill up the traction battery and get the friction brakes hot, 'B' is of little use.

 

Johan you're car is ruined. I'll give you ten bucks for it and take it off your hands. Best you apply that money to a new purchase.

 

What I found interesting was that when the traction battery filled up on a long downhill mountain road (the cruise control was engaged), the car automatically switched to "B" to keep the car from accelerating to warp factor 3.

You're right, driving in "B" shouldn't cause any problems.

 

Cool! Is that supposed to happen in cruise control?

 

Did it really go into 'B' as indicated on the dashboard, or did it just wind up the ICE into a semi-screaming mode to moderately retard the speed increase?

Mine does only the later, and the engine screams less than it would in real 'B' mode. 'B' and Cruise Control are mutually exclusive.

 

JE Sukara - When using the cruise control, the car tries to maintain the speed you set, so when going downhill it will automatically use rather agressive regenerative braking to slow the car down. The result is exactly the same as stepping on the brake to maintain a downhill speed. With cruise control disengaged, there will be only a small amount of regenerative braking when going downhill unless you step on the brake yourself. So, I typically engage cruise control before I start down a hill and let the car do the work with little concentration on my part. Of course, when the traction battery fills up from regenerative braking, the only other options it has is regular braking (from you stepping on the brake pedal) or engine braking (by either you or the cruise control putting the transmission into "B").

fuzzy1 - As I recall, there was no indication on the dashboard that the transmission was in "B" but I can't be positive on that. It was obvious that the little engine was really screaming. Once the hill flattened out, the car automatically went back to normal (no engine braking) without any action on my part.

johan314 - As I told fuzzy1, I don't remember seeing "B" show up on the dashboard when the cruise control used engine braking to try to slow the car down, but I could be wrong on that. Once the hill flattened out, the car went back to normal and definitely was not in "B" anymore.

 

I'll have to play with this a bit more, but will suggest that you weren't in real 'B' mode. If you get into this situation again, try shifting to 'B' as a test. On some of my hills, I believe this will cause a noticeable boost to the pitch of the engine's scream, and RPM will jump from low-mid-3000s in CC to low-4000s in B.

 

Good read on driving tricks and B Mode.
Toyota Prius/Driving tricks - Wikibooks, open books for an open world

 

I thought it was "B" for engine braking, as I use this mode when descending hills when the battery is full. The engine speeds up quite a bit.

 

Hi Drafty. When the battery is full from descending a hill, then that particular mode (the engine speeds up quite a bit) occurs whether or not you're in "B" mode. It does the same thing in "D" mode too, that's part of the confusion here.

What "B" mode does do is two things.

1. Keeps the engine turning (though not necessarily rapidly) even when you're foot is off the gas. This increases the losses and helps to slow the car.

2. It causes the prius to regeneratively brake more aggressively. That is, the mild regenerative braking (that the prius normally does when you're off the gas) to simulate engine braking, is increased to a higher level in "B" mode.

The effect of 1 and 2 above is to make the prius decelerate considerably more rapidly when you take your foot off the gas. Some people feel more comfortable in this mode when driving in mountainous terrain, it does indeed give a similar feeling to driving a manual car in a lower gear.

Now in both D and B modes, when the battery reaches its maximum state of charge then the regenerative braking can no longer operate unless it has somewhere else (apart from the battery) to dump the generated electric power. Here the Prius begins using one of it's motor/generators (MG1) to spin the engine fairly quickly in order to use up that unwanted electric power. Yes this is very similar to what "B" mode does all the time (as per 1 above), but the key difference is that the engine is typical rotated much faster here.

 

Hi Uart,

Thanks for that explanation. These are things that aren't really in the manual either I suspect.

 

Per gear B: We watched the video they gave us with the car (2014 Prius II). It recommends using gear "B" for hilly areas and suggested using it both going up and down. Does that make sense? And do we leave it on cruise when in hilly areas?

 

B mode has no effect unless you are braking, so it is harmless going uphill. B mode and Cruise Control are mutually exclusive in the Gen 2, I suspect it is true for every Prius.

 

B is the same as D when you're pressing the gas, so it doesn't really matter if you leave it in B going up hill. I don't know about the Gen3, but my Gen2 doesn't allow criuse in B.