VSA System Description - VSA Modulator
The VSA modulator unit consists of the inlet solenoid valve, the outlet solenoid valve, the VSA NO (normally open) solenoid valve, the VSA NC (normally closed) solenoid valve, the reservoir, the pressure sensor, and the pump motor.
The hydraulic control has three modes of ABS action; pressure intensifying, pressure retaining, and pressure reducing. Pressure intensifying mode (VSA) is a combination of the TCS, VSA, and brake assist action.

Mode
VSA NO Solenoid Valve
VSA NC Solenoid Valve
Inlet Solenoid Valve
Outlet Solenoid Valve
Brake Fluid
Pressure intensifying mode
open
closed
open
closed
Master cylinder fluid is pumped out to the caliper.
Pressure retaining mode
open
closed
closed
closed
Caliper fluid is retained by the inlet and outlet solenoid valves.
Pressure reducing mode
open
closed
closed
open
Caliper fluid flows through the outlet solenoid valve to the reservoir.
Pressure intensifying mode (VSA)
closed (current control )
open
open
closed
Master cylinder fluid is pumped out by the pump through the VSA NC solenoid valve to the caliper.
Caliper fluid pressure exceeds master cylinder.
The VSA modulator unit controls amount of intensified fluid pressure to respond to each mode through current control of VSA NO solenoid valve.