Engine braking is the process of slowing down a vehicle by using the retarding forces within an internal combustion engine, instead of using additional external braking mechanisms such as friction brakes or magnetic brakes. When the accelerator pedal is released, the fuel injection ceases and the throttle valve closes almost completely, greatly restricting forced airflow from, for example, a turbocharger. This causes a strong manifold vacuum which the cylinders have to work against, sapping much of the potential energy out of the system over time and producing the majority of the engine-braking effect.
Engine braking is beneficial to a vehicle because it helps reduce brake wear, which can eventually cause wear and tear to the braking system. It is also more fuel-efficient than normal braking because when engine braking is used, the engine stops consuming fuel.
To perform engine braking, the driver can step off the accelerator and downshift gears instead of pressing on the brake pedal. Some automatic transmissions do allow drivers to change gears with either a lever or a paddle shifter.
It is important to note that engine braking does not harm the engine at all, as engines are designed to run at thousands of revs per minute for hours at a time.
