The ABS modulator consists of the inlet solenoid valve, the outlet solenoid valve, the reservoir, the pump, the pump motor, and the damping chamber. The modulator reduces the caliper fluid pressure directly. It is a circulating-type modulator because the brake fluid circulates through the caliper, the reservoir, and the master cylinder. The hydraulic control has three modes; pressure intensifying, pressure retaining, and pressure reducing. 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.

BRAKE FLUID SPECIFICATION

Mode

Inlet Solenoid Valve

Outlet Solenoid Valve

Brake Fluid

Pressure intensifying mode

open

closed

Master cylinder fluid is pumped out to the caliper.

Pressure retaining mode

closed

Caliper fluid is retained by the inlet and outlet valves.

Pressure reducing mode

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⁾	The motor will keep 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

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