Automobile & Light Truck Certification Test A5 BrakesPower Assist Unit Diagnosis and RepairEasy
Which of the following is a common characteristic of a vehicle equipped with an electro-hydraulic power brake system (EHPB) compared to a traditional vacuum-assist system?
- AA direct mechanical link between the brake pedal and master cylinder.
- BIndependence from engine vacuum for brake assist.
- CA larger, more visible vacuum reserve tank.
- DA requirement for specialized power steering fluid.
Show answer & explanationAnswer & explanation
Correct answer: B. Independence from engine vacuum for brake assist.
Electro-hydraulic power brake (EHPB) systems use an electric motor to power a hydraulic pump, which then provides pressure for brake assist. This design makes them independent of engine vacuum, a key advantage, especially for vehicles with low engine vacuum or electric powertrains.
Why the other options are wrong
- A. While some EHPB systems retain a mechanical backup, the primary assist is electro-hydraulic, often with a 'brake-by-wire' feel, meaning the direct mechanical link is less emphasized for primary assist.
- C. EHPB systems do not use engine vacuum, therefore they do not require a vacuum reserve tank.
- D. EHPB systems use standard brake fluid (DOT 3/4/5.1), not specialized power steering fluid, as they are part of the brake system, not steering.
Electro-Hydraulic Power Brake (EHPB)
A brake assist system that uses an electric motor-driven hydraulic pump to provide power braking, eliminating reliance on engine vacuum.
- Common in hybrid/electric vehicles and some gasoline vehicles.
- Provides consistent brake assist regardless of engine vacuum.
- Often integrates ABS, traction control, and stability control functions.
Memory trick: EHPB is electric, not engine vacuum – like a 'battery-powered' brake.