Automobile & Light Truck Certification Test A5 BrakesPower Assist Unit Diagnosis and RepairHard
A technician is inspecting a vehicle with a hydro-boost brake system. The customer complains of a hard brake pedal and excessive effort required for steering, especially at low engine RPMs. Upon inspection, the power steering fluid reservoir is found to be below the 'add' mark, and the fluid appears dark and burnt. What is the MOST likely cause?
- AA failing power steering pump.
- BA faulty hydro-boost accumulator.
- CAir in the hydro-boost system.
- DA restricted high-pressure power steering hose.
Show answer & explanationAnswer & explanation
Correct answer: A. A failing power steering pump.
Hydro-boost systems use the power steering pump to generate hydraulic pressure for both power steering and brake assist. A failing power steering pump, indicated by low fluid and dark/burnt fluid (suggesting overheating and wear), would result in insufficient pressure for both systems, leading to a hard brake pedal and heavy steering.
Why the other options are wrong
- B. A faulty accumulator would primarily affect brake pedal feel (e.g., hard pedal after several applications) but wouldn't typically cause heavy steering or dark, burnt fluid.
- C. Air in the system would cause noise and erratic assist, but low fluid and burnt fluid point to component wear, not just air.
- D. A restricted high-pressure hose would cause issues, but the discolored fluid and dual system failure point more strongly to the pump itself.
Hydro-Boost System
A power brake assist system that uses hydraulic pressure from the power steering pump instead of engine vacuum to amplify brake pedal force.
- Uses power steering pump for pressure.
- Assists both braking and steering.
- Pump failure affects both systems.
Memory trick: Hydro-Boost shares the pump's might, if it fails, both systems fight!