Engine braking

This causes fuel injection to cease and the throttle valve to close almost completely, greatly restricting forced airflow from, for example, a turbocharger.

The restriction 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.

[2] While some of the braking force is produced due to friction in the drive train, this is negligible compared to the effect from the manifold vacuum caused by the air-flow restriction.

This type of brake produces extreme amounts of noise pollution if there is no muffler on the intake manifold of the engine, loud enough to disturb the surrounding area.

Numerous cities, municipalities, states, and provinces have banned the use of unmuffled compression brakes, which are typically only legal on roads away from populations.

In hybrid vehicles, the engine runs on electric power to dissipate excess energy when the battery has been fully recharged.

A well-executed rev-match in the same setting minimizes stresses on transmission components, so engine braking does the work of slowing the vehicle.

Improper engine braking technique can cause the wheels to skid (also called shift-locking), especially on slippery surfaces, as a result of too much deceleration.

If the driver reduces engine braking by shifting back up, or disengaging the clutch on a manual transmission, traction can be regained.

In hybrid electric vehicles, like the Toyota Prius, engine braking is simulated by the computer software to match the feel of a traditional automatic transmission.

For long downhill runs, the "B" mode acts like a lower gear, using the higher RPM of the internal combustion engine to waste energy, preventing the battery from being overcharged.