* Brake booster: This is the most common and important function. The vacuum pump provides the vacuum needed to assist the driver in applying the brakes. Without it, braking would require significantly more force.
* Cruise control: Some cruise control systems utilize vacuum to operate the throttle.
* Transmission shifting (some older models): Older automatic transmissions might use vacuum for shifting gears. Modern automatics usually rely on electronically controlled hydraulic systems.
* Other vacuum-operated accessories: Some older vehicles might use vacuum for other systems like power locks or climate control, though this is less common in modern diesel vehicles.
Essentially, the vacuum pump replaces the function of the intake manifold vacuum that's more readily available in gasoline engines. Because diesel engines' intake manifolds have less vacuum due to the higher pressures involved, a separate vacuum pump is necessary.
