Brake Systems Flashcards

To test a vacuum brake booster, the technician pumps the pedal with the engine off, holds pressure on the pedal, and starts the engine. What is a normal result?

Answer: The pedal drops slightly

Once engine vacuum reaches the booster, it adds assist and the held pedal moves down slightly.

What type of signal does a passive (magnetic) ABS wheel speed sensor produce?

Answer: An AC voltage whose frequency and amplitude increase with wheel speed

A passive sensor creates an AC sine wave as the tone ring teeth pass, and both frequency and voltage rise with speed.

An ABS wheel speed sensor sets a fault code only at very low speeds. What could cause this?

Answer: An excessive sensor air gap

A large air gap weakens the passive sensor signal, and the signal is weakest at low speed.

What powers a Hydro-boost brake assist system?

Answer: Pressure from the power steering pump

Hydro-boost uses hydraulic pressure from the power steering pump to assist the brakes.

The amber ABS warning lamp stays on, but the red brake lamp is off. What does this usually mean?

Answer: ABS is disabled, but normal base brakes still work

An amber ABS lamp means the anti-lock function is turned off, but the base hydraulic brakes still work.

Which test result shows that glycol-based brake fluid should be replaced?

Answer: Copper content of 200 ppm or more

Copper above about 200 ppm shows the corrosion inhibitors are used up, so the fluid should be replaced.

Before replacing rear pads on a vehicle with an electronic parking brake (EPB), what is usually required?

Answer: Use a scan tool or service mode to retract the EPB actuators

EPB calipers need the actuator motors retracted through a scan tool or service procedure before the pistons can be pushed back.