Automobile & Light Truck Certification Test A5 BrakesPower Assist Unit Diagnosis and RepairHard
A vehicle with an electro-hydraulic power steering system (EHPAS) that also provides power brake assist experiences a complete loss of power steering and power brakes. The technician confirms the serpentine belt is intact and the engine is running. What is the MOST likely cause of this dual failure?
- AA failure of the EHPAS electric pump motor.
- BA low brake fluid level in the master cylinder reservoir.
- CAir in the power steering hydraulic lines.
- DA fault in the ABS hydraulic control unit.
Show answer & explanationAnswer & explanation
Correct answer: A. A failure of the EHPAS electric pump motor.
Electro-hydraulic power steering systems, sometimes called 'Hydraulic Brake Boost' or 'Hydro-Boost' systems, use a single electric pump to generate hydraulic pressure for both power steering and power brake assist. A failure of this electric pump would simultaneously disable both functions.
Why the other options are wrong
- B. Low brake fluid would primarily affect braking, not power steering, and typically wouldn't cause a complete, sudden loss of assist for both.
- C. Air in the power steering lines would cause noisy operation and reduced assist, but not a complete, simultaneous loss of both steering and braking assist if the pump is still running.
- D. The ABS hydraulic control unit primarily manages ABS functions and wouldn't typically cause a complete loss of base power steering and brake assist simultaneously.
Electro-Hydraulic Power Steering (EHPAS)
A system that uses an electric motor to drive a hydraulic pump, providing power assist for steering and sometimes braking, independent of engine speed.
- Electric motor drives hydraulic pump.
- Can provide assist to both steering and braking.
- Failure of electric pump affects both systems.
Memory trick: The electric heart of EHPAS, if it stops, steering and brakes are in a pass.