When testing a hydraulic brake with power assist, when you turn the engine on the pedal should?

The correct answer is that the pedal should drop slightly when testing a hydraulic brake with power assist and turning the engine on. This slight drop indicates that the power brake booster is functioning properly. When the engine starts, the vacuum or hydraulic pressure in the power assist unit begins to engage, which provides additional force to the brake system, resulting in a minor drop of the brake pedal.

This behavior is expected because the booster helps in reducing the effort needed to press the brake pedal, thereby making braking more effective. A slight drop confirms that the system is properly engaging and aiding the driver in achieving sufficient braking power.

If the pedal were to drop to the floor, this could suggest significant issues such as air in the brake lines or a malfunctioning brake system that requires immediate inspection. Conversely, if the pedal stays where it is, it may indicate that the power assist is not activating, which can also be a sign of a problem. A drop halfway is also not typical, as the reaction of the pedal should be minimal. Thus, a slight drop after the engine is turned on serves as an indicator of the power assist working as intended.