Automobile & Light Truck Certification Test A5 BrakesHydraulic System Diagnosis and RepairMedium
A technician is performing a diagnostic on a vehicle with an Anti-lock Braking System (ABS) that exhibits a 'hard pedal' symptom, but only when actively engaging ABS. The conventional braking feels normal. Which of the following components is MOST likely at fault?
- AABS Hydraulic Control Unit (HCU) pump motor
- BBrake booster check valve
- CVacuum hose to the brake booster
- DMaster cylinder primary cup seal
Show answer & explanationAnswer & explanation
Correct answer: A. ABS Hydraulic Control Unit (HCU) pump motor
A hard pedal specifically during ABS engagement suggests an issue with the ABS system's ability to modulate pressure. The HCU pump motor is responsible for generating and maintaining pressure within the ABS system during active ABS events, and its failure would lead to a hard pedal during those times.
Why the other options are wrong
- B. A faulty brake booster check valve would cause a hard pedal at all times, not just during ABS activation.
- C. A vacuum hose issue would cause a hard pedal at all times, not specifically during ABS engagement.
- D. A master cylinder primary cup seal issue would typically cause a soft or sinking pedal, not a hard pedal during ABS activation.
ABS HCU Pump Motor
An electric motor within the ABS Hydraulic Control Unit (HCU) that rapidly cycles to generate and release hydraulic pressure to individual wheels during anti-lock braking events.
- Responsible for pressure modulation during ABS events.
- Failure can lead to a hard pedal during ABS activation.
- Often controlled by the ABS control module.
Memory trick: ABS hard pedal, motor not pumping, wheels not stopping.