What does the brake pedal do when the engine is started during a Power Assist Braking System check?

When conducting a Power Assist Braking System check, the correct response is that the brake pedal drops slightly when the engine is started. This occurs due to the activation of the brake booster, which uses vacuum or hydraulic pressure to assist in braking.

When the engine is off, there is no power assist, and the brake pedal may feel stiff or firm as it relies solely on the driver's foot pressure to engage the brakes. However, once the engine is started, the brake booster activates and produces a slight drop in pedal height as it allows for greater braking force to be applied with less effort from the driver. This characteristic indicates that the brake booster is functioning correctly, providing the necessary assistance for effective braking.

The other options would not accurately represent the expected behavior of the brake pedal during such a system check. For instance, if the pedal were to stay firm or become soft without the expected slight drop, it would suggest potential issues with the power assist function. Understanding this system is crucial for ensuring vehicle safety and effective braking performance.