Acura RDX 2019 Owner's Manual page 496

uuBrakinguBrake Assist System
Brake Assist System
Designed to assist the driver by generating greater braking force when you depress
the brake pedal hard during emergency braking.
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Brake assist system operation
Press the brake pedal firmly for more powerful braking.
When brake assist operates, the pedal may wiggle slightly and an operating noise
may be heard. This is normal. Keep holding the brake pedal firmly down.
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