Correct answer
There is air in the hydraulic circuit.
Air in the circuit, which is compressible and can impair pressure transmission to the brakes. This symptom alone does not identify a single fault: the circuit, possible leaks and other components require inspection. Do not continue driving with abnormal braking or rely on pumping as a repair; stop safely and request assistance and professional diagnosis. Bleeding follows the manufacturer’s procedure when appropriate.
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Loss of brake-servo assistance, whose characteristic effect is a harder pedal.
There is air in the hydraulic circuit.
Worn tyre tread, without a fault in the braking circuit.
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