Brake System Service Flashcards

How does the output of a passive (magnetic) wheel speed sensor change as wheel speed increases?

Answer: It produces an AC signal whose frequency and amplitude increase

Passive sensors generate AC voltage, and both frequency and amplitude rise with tone ring speed.

What is the likely result of an excessive air gap between a magnetic wheel speed sensor and its tone ring?

Answer: A weak or missing signal, especially at low speeds

A larger gap weakens the magnetic field change, so the sensor output may be too low for the module to read at low speed.

If the amber ABS warning lamp is on but the red brake warning lamp is off, what is generally true?

Answer: Base brakes should still function normally without ABS assist

An amber ABS lamp alone signals an ABS fault, while normal base braking remains available.

When replacing a component on many ABS-equipped vehicles, what is often required to fully bleed the hydraulic control unit?

Answer: Using a scan tool to cycle the ABS valves and pump during bleeding

Many systems need a scan tool automated bleed to purge air trapped in the modulator valves and passages.

During a hard stop on dry pavement, a driver feels rapid pedal pulsation and hears a buzzing noise from an ABS-equipped vehicle. What does this usually indicate?

Answer: Normal ABS operation

Pedal pulsation and pump/valve noise are normal when ABS is cycling to prevent lockup.

On many modern vehicles, what replaces the mechanical proportioning valve?

Answer: Electronic brake force distribution (EBD) using the ABS modulator

EBD uses wheel speed data and ABS valves to electronically limit rear brake pressure.

Which statement describes an active (Hall-effect or magnetoresistive) wheel speed sensor?

Answer: It requires a supply voltage and outputs a digital square-wave signal

Active sensors are powered by the module and produce a digital signal that can read speeds near zero.