The modulator unit consists of the inlet solenoid valve, the outlet solenoid valve, the TCS NO (normally open) solenoid valve, the ESV NC (normally closed) solenoid valve, the reservoir, the pump, and the pump motor.

The hydraulic control has three modes of ABS action; pressure intensifying, pressure retaining, and pressure reducing. Pressure intensifying (VSA) mode is combined of the TCS, VSA, CAS, HSA and brake assist action.

The hydraulic circuit is an independent four channel type; one channel for each wheel.

Fig 1: Modulator Unit Circuit Diagram

Courtesy of AMERICAN HONDA MOTOR CO., INC.

Mode

TCS NO Valve

ESV NC 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

Caliper fluid is retained by the inlet and outlet valves.

Pressure reducing mode

open

closed

open

Caliper fluid flows through the outlet valve to the reservoir.
The motor pumps the reservoir fluid through the damping chamber to the master cylinder⁽¹⁾.

Pressure adding mode

closed

open

closed

Master cylinder fluid is pumped out by the pump through the ESV NC valve to the caliper.
Caliper fluid pressure exceeds master cylinder pressure.

⁽¹⁾	The motor will continue running until the operation of the one anti-lock brake control is finished with the first pressure reducing mode.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Modulator Unit

Use the Manual With the Right Hardware

When to See a Mechanic

Rather have a pro handle this?