Electronic Brake Control Module: Description and Operation

MAIN CONTROL
The ABS control unit detects the wheel speed based on the wheel sensor signal it received, then it calculates the vehicle speed based on the detected wheel speed. The control unit detects the vehicle speed during deceleration based on the rate of deceleration.
The ABS control unit calculates the slip rate of each wheel, and it transmits the control signal to the modulator unit solenoid valve when the slip rate is high.
The pressure reduction control has three-modes: pressure reduction, pressure retaining, and pressure intensifying.

SELF-DIAGNOSIS
1. The ABS control unit is equipped with a main Central Processing Unit (CPU)s and a sub CPU, that check each other for problems.
2. The CPUs check the circuit of the system.
3. Self-diagnosis can be classified into two categories.
- Initial diagnosis: Performed right after the engine starts and until the ABS indicator goes off.
- Regular diagnosis: Performed right after the initial diagnosis until the ignition switch is turned OFF.
4. When a problem is detected by self-diagnosis, the system:
- Turns the fail-safe relay OFF.
- Turns the solenoid valve OFF.
- Turns the pump motor OFF.
- Turns the ABS indicator ON.





SELF DIAGNOSTIC TABLE





OPERATION MODE TABLE

ON-BOARD DIAGNOSIS FUNCTION
The ABS control unit is connected to the 16P Data Link Connector.
The ABS can be diagnosed with the Honda PGM Tester.
The ALB Checker cannot be used with this system. For air bleeding, and checking wheel sensor signals, use the Honda PGM Tester. See the Honda PGM Tester user's manuals for specific operating instructions.

ABS MODULATOR





The ABS modulator consists of the inlet solenoid valve, outlet solenoid valve, reservoir, pump, 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, reservoir and the master cylinder.
The hydraulic control has three modes: pressure reduction, pressure retaining and pressure intensifying.
The hydraulic circuit is the independent four channel-type, one channel for each wheel.

Pressure intensifying mode:
Inlet valve open, outlet valve closed
Master cylinder fluid is pumped out to the caliper.

Pressure retaining mode:
Inlet valve closed, outlet valve closed
Caliper fluid is retained by the inlet valve and outlet valve.

Pressure reduction mode:
Inlet valve closed; outlet valve open
Caliper fluid flows through the outlet valve to the reservoir.

Motor operation mode:
When starting the pressure reduction mode, the pump motor is ON.
When stopping ABS operation, the pump motor is OFF.
The reservoir fluid is pumped out by the pump, through the damping chamber, to the master cylinder.

WHEEL SPEED AND MODULATOR CONTROL





When the wheel speed drops sharply below the vehicle speed, the inlet valve closes to retain the caliper fluid pressure. When the wheel speed drops further, the outlet valve opens momentarily to reduce the caliper fluid pressure. The pump motor starts at this time.
As the wheel speed is restored, the inlet valve opens momentarily to increase the caliper fluid pressure.

WHEEL SENSOR








The wheel sensors are the magnetic contactless type. As the gear pulser teeth rotate past the wheel sensor's magnetic coil, AC current is generated. The AC frequency changes in accordance with the wheel speed. The ABS control unit detects the wheel sensor signal frequency and thereby detects the wheel speed.