310S Brake Systems 3 — Questions and Answers
Question 1: What is the function of the wheel speed sensor in an ABS system?
- To measure tire pressure
- To monitor individual wheel rotational speed and send data to the ABS module for skid detection (Correct answer)
- To activate the brake lights
- To measure brake rotor temperature
Correct answer: To monitor individual wheel rotational speed and send data to the ABS module for skid detection
Wheel speed sensors generate a signal proportional to wheel rotational speed. The ABS module compares all four wheel speeds; if one decelerates faster than the others (indicating lockup), it modulates brake pressure to that wheel.
Question 2: What is the purpose of the parking brake equalizer?
- To adjust the parking brake automatically
- To distribute equal cable force to both rear brakes when the parking brake is applied (Correct answer)
- To release the parking brake when driving
- To connect the parking brake to the hydraulic system
Correct answer: To distribute equal cable force to both rear brakes when the parking brake is applied
The parking brake equalizer splits the single parking brake cable into two cables (one for each rear wheel) and ensures equal tension is applied to both sides so the vehicle is held evenly.
Question 3: When measuring brake rotor thickness with a micrometer, where should measurements be taken?
- At the thickest point only
- At multiple points around the rotor to check for thickness variation (parallelism) (Correct answer)
- At the centre hub area
- Only at the outer edge of the friction surface
Correct answer: At multiple points around the rotor to check for thickness variation (parallelism)
Brake rotor thickness must be measured at multiple points (typically 8-12) around the friction surface to detect thickness variation (parallelism). Variation as small as 0.013 mm can cause pedal pulsation.
Question 4: What is the function of the ABS hydraulic modulator?
- To boost brake pedal pressure
- To independently control brake pressure to each wheel by holding, releasing, or reapplying pressure during ABS activation (Correct answer)
- To distribute fluid between the front and rear circuits
- To store pressurized brake fluid
Correct answer: To independently control brake pressure to each wheel by holding, releasing, or reapplying pressure during ABS activation
The ABS modulator contains solenoid valves and a pump. During ABS activation, it can isolate (hold), release (decrease), or reapply (increase) brake pressure to individual wheels many times per second to prevent lockup.
Question 5: What causes a hard brake pedal with poor stopping power?
- Air in the brake lines
- A failed vacuum brake booster or loss of vacuum supply (Correct answer)
- Worn brake pads
- A leaking brake caliper
Correct answer: A failed vacuum brake booster or loss of vacuum supply
A hard pedal with poor braking indicates the brake booster is not providing power assist. This can be caused by a failed booster diaphragm, a cracked or disconnected vacuum hose, or a faulty check valve.
Question 6: What is the purpose of the brake fluid level sensor in the master cylinder reservoir?
- To measure the quality of the brake fluid
- To illuminate the brake warning light when fluid drops below a safe level, indicating a possible leak or worn pads (Correct answer)
- To control the brake fluid pressure
- To activate the ABS system
Correct answer: To illuminate the brake warning light when fluid drops below a safe level, indicating a possible leak or worn pads
The fluid level sensor triggers the brake warning light when fluid drops below the minimum level, alerting the driver to a potential hydraulic leak or significantly worn brake pads that have displaced fluid into the calipers.
310S Brake Systems 3
What is the function of the wheel speed sensor in an ABS system?