Automobile & Light Truck Certification Test A5 BrakesAnti-lock Brake System (ABS) Diagnosis and RepairMedium
A vehicle with traction control (TCS) experiences wheel spin on a slippery surface. To regain traction, the TCS activates. Which component within the ABS hydraulic control unit (HCU) is primarily responsible for reducing brake fluid pressure to the spinning wheel?
- AThe ABS pump motor
- BThe accumulator
- CThe outlet solenoid valve
- DThe inlet solenoid valve
Show answer & explanationAnswer & explanation
Correct answer: C. The outlet solenoid valve
The outlet solenoid valve, when opened, allows brake fluid pressure to be released from the caliper/wheel cylinder back to the master cylinder or accumulator, thus reducing braking force on the spinning wheel.
Why the other options are wrong
- A. The ABS pump motor increases pressure or returns fluid, but doesn't primarily reduce pressure to a specific wheel.
- B. The accumulator stores excess fluid and pressure, but doesn't directly reduce pressure to a specific wheel.
- D. The inlet solenoid valve isolates the caliper from the master cylinder or allows pressure to build, not reduce it.
ABS Solenoid Valves
Electrically controlled valves within the ABS HCU that modulate brake fluid pressure to individual wheels during ABS, TCS, or ESC events.
- Inlet valves control pressure application to the wheel.
- Outlet valves control pressure release from the wheel.
- Work in conjunction with the pump and accumulator.
Memory trick: Inlet IN, Outlet OUT, Pump POWER, Accumulator STOUT!