This feature of the Toyota Prius is a complete mystery to most owners

Matthew DeBord/Business Insider

The gearshift on the Toyota Prius is something of a legendary feature.

It sticks out of the dashboard like the shifter on an old Alfa Romeo. But it's far from old school.

In fact, it's more like a video-game joystick than an automotive component. 

The Prius is a complex piece of electrical and mechanical engineering, plus software, and the gearshift is one of the driver's primary connections with that.

However, there's an aspect of the Prius gearshift that has always been shrouded in mystery.

As you can see from the photo below, you have the usual "Reverse," "Neutral," and "Drive" selections. No "Park," but there's a button for that on the dash. (This is the shifter from a 2016 Prius that we reviewed, by the way, but the component has been on vehicle for a while).

Matthew DeBord/Business Insider

Simple enough. 

But what about that "B?"

Well, it stands for "Braking," and this is where the mystery comes in.

Because the Prius has "regenerative braking," which returns otherwise wasted energy from braking to the hybrid drivetrain, a lot of folks seem to think that "B" improves the re-gen and sends more energy back into the system.

But that's completely wrong. I know because I was wrong about it, and I'm supposed to know something about cars!

The "B" creates something called "engine braking," which mimics the behavior of a traditional transmission: it fakes a downshift to slow the Prius if it's descending a hill.

Why? To keep the brakes from being overloaded if you're on a long, steep grade. That's when you would want to use the feature — just like a lower selection on an old-fashioned automatic transmission, or a lower gear in a stickshift.

So there, mystery solved! Myths debunked!

Now the next time you're in a Prius and the driver is tooling around in "B," tell them that it's pointless and that they should keep it it "D."

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