What effect might air in the brake hydraulic system have?

Air in the brake hydraulic system can lead to a spongy brake pedal due to the compression of the air bubbles within the hydraulic fluid. In a properly functioning hydraulic brake system, the brake fluid should be incompressible, allowing for the effective transfer of force from the brake pedal to the braking components. When air is present, it introduces compressibility, which means that instead of solid pressure being applied to the brake components, the pressure is dissipated by the compressible air. This results in the brake pedal feeling soft or spongy when pressed, which compromises the driver’s ability to maintain firm control over braking.

The other effects listed, such as enhanced braking power, increased fuel efficiency, and reduced engine noise, are not related to the presence of air in the brake hydraulic system, and in fact, air leads to diminished performance in braking capability, posing safety risks.