Mazda CX-3 Owner's Manual page 266

When Driving
Brake
When the brake pedal is depressed hard
or depressed more quickly, a motor/
pump operation noise may be heard.
This is a normal effect of the brake
assist and does not indicate a
malfunction.
The brake assist equipment does not
supersede the functionality of the
vehicle's main braking system.
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CX-3_8GT4-EE-18D_Edition8_old 2019-11-14 12:53:52