Applications
As soon as the accelerator is released and the throttle closes, engine braking comes into effect as long as the wheels remain connected via the transmission to the engine. (A clutch or a torque converter can disengage the wheels or absorb braking energy.) The braking force varies depending on the engine, but also what gear the vehicle is in (Generally, the lower the gear, the higher the braking effect as long as the wheels continue to maintain traction with the road surface).
Engine braking passively reduces wear on brakes and helps a driver maintain control of the vehicle. Active use of engine braking (shifting into a lower gear) is advantageous when it is necessary to control speed while driving down very steep and long slopes. It should be applied before regular disk or drum brakes have been used, leaving the brakes available to make emergency stops. The desired speed is maintained by using engine braking to counteract the gravitational acceleration.
Improper engine braking technique can cause the wheels to skid (also called shift-locking), especially on slippery surfaces such as ice or snow, as a result of too much deceleration. As in a skid caused by overbraking, the vehicle will not regain traction until the wheels are allowed to turn more quickly; the driver must reduce engine braking (shifting back up or disengaging the clutch on a manual transmission) to regain traction.
Engine braking is intrinsically available in non hybrid vehicles with gasoline-powered internal combustion engines, regardless of transmission type. With diesel engines however, there is no intrinsic engine braking effect so more care must be taken. Turbo-diesel engines, on the other hand, generally have a more noticeable engine braking effect due to the turbo stalling when the accelerator is released and increasing the back-pressure in the exhaust.
In almost all cases, it is active when the foot is lifted off the accelerator, the transmission is not in neutral, the clutch is engaged and a freewheel is not engaged. Using frequent engine braking while changing down gears may cause higher than normal wear on clutch plates if the driver uses the poor gear-changing technique of slipping the clutch to raise the engine's rpm to match the transmission speed, instead of rev-matching using the throttle. This is in contrast to "conventional" braking where the engine's rpm is already reduced prior to the downshift.
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 higher RPM in the internal combustion engine to waste energy, preventing the battery from becoming overcharged. Almost all electric and hybrid vehicles are able to convert kinetic motion into electricity, i.e. regenerative brakes, but this is not the same as engine braking.
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