Home › CDL Practice Tests › Air Brakes Questions › Question 204
How does ABS know a wheel is about to lock up?
- A.The driver tells the system by tapping the pedal twice
- B.A sensor in the air tank measures total pressure only
- C.Wheel speed sensors monitor each controlled wheel's rotation and signal the controller when one slows much faster than the others
- D.The system uses the speedometer alone
Correct answer
C. Wheel speed sensors monitor each controlled wheel's rotation and signal the controller when one slows much faster than the others
Why
Comparing wheel speeds lets the controller spot a wheel that is decelerating toward a slide before it fully locks. The controller then holds, reduces, or reapplies pressure at that wheel many times per second.
Manual topic: Air Brakes - ABS · From the Air Brakes practice bank (AB-204).