A lot of people ask us for the purpose of the “B” mode in the Toyota Prius transmission and its intended use.
What is meaning of B on the Gear selector lever ?
We have written a small article for the understanding of this mode and its right use can save the costly transmission from breaking down.
A driver can use B mode on the Toyota Prius all the way he wants, but the intended purpose of B mode is when coasting down long gradients (downhill), just like using lower gears in traditional vehicles. During long descents, the traction battery can become “full” and regenerative braking will be stopped in order to protect the battery from over-charging. A classic case is while coasting down from Salt range on the Motorway M-2 ,Murree Expressway , Babusar Top and Khunjerab Top.
All subsequent braking is then via the friction brakes / brake pads. To help keep the friction brakes from over-heating, B mode uses the resistance of spinning the ICE (Internal Combustion engine) to help with additional braking. The engine will kick in and the driver may get confused why its kicking in because the batteries are at full but it is actually providing resistance to the gearbox to keep brakes wear and tear at minimum by putting fake load on the gearbox.