ABS System Description (ABS)

ABS System Description

ABS Control Unit Inputs and Outputs for 25P Connector

Terminal number	Wire color	Terminal sign	Description	Measurement (Disconnect the ABS control unit 25P connector)
				Terminals	Conditions				Voltage
2	ORN/BLK	FR +B	Detects right-front wheel sensor signal	———	———				———
3	BRN/ WHT	FL-GND	Detects left-front wheel sensor signal	———	———				———
4	WHT/ BLK	STOP	Detects brake switch signal	4- GND	Brake pedal		Pressed		Battery Voltage
							Released		Below 0.3 V
5	RED	RL-GND	Detects left-rear wheel sensor signal	———	———				———
6	GRN/ YEL	RR +B	Detects right-rear wheel sensor signal	———	———				———
8	WHT	+B-FSR	Power source for the fail-safe relay	8- GND	At all times				Battery Voltage
9	WHT/ RED	+B-MR	Power source for the motor relay	9- GND	At all times				Battery Voltage

Terminal number	Wire color	Terminal sign	Description	Measurement (Disconnect the ABS control unit 25P connector)
				Terminals	Conditions				Voltage
10	BLU	DIAG-K	Communications with Honda PGM Tester or HDS	———	———				———
11	BLK/ RED	EBD	Drives brake system indicator	11- GND	Brake system indicator			OFF	Battery voltage
								ON	Battery voltage (via brake fuild level switch or parking brake switch)
								ON	Below 0.3 V (via ABS control unit)
12	BLU/ WHT	FL +B	Detects left-front wheel sensor signal	———	———				———
13	BRN	SCS	DTC indication	———	———				———
14	YEL/ RED	RL +B	Detects left-rear wheel sensor signal	———	———				———
15	BLU/ YEL	RR-GND	Detects right-rear wheel sensor signal	———	———				———
16	YEL	IG1	Power source for activating the system	16- GND	Ignition switch ON (II)				Battery Voltage
18	PNK	FR-GND	Detects right-front wheel sensor signal	———	———				———
21	BLU/ RED	ABS	Drives ABS indicator	21- GND	ABS indicaor (Ignition switch ON (II))			ON	About 6 V
								OFF	Below 0.3 V
24	BLK	GND	Ground for the ABS modulator-control unit	———	———				———
25	BLK	MR-GND	Ground for the pump motor	———	———				———

Features

When the brake pedal is pressed during driving, the wheels can lock before the vehicle comes to a stop. In such an event, the maneuverability of the vehicle is reduced if the front wheels are locked, and the stability of the vehicle is reduced if the rear wheels are locked, creating an extremely unstable condition. The ABS precisely controls the slip rate of the wheels to ensure maximum grip force from the tyres, thereby ensuring the maneuverability and stability of the vehicle.
The ABS calculates the slip rate of the wheels based on the vehicle speed and the wheel speed, then it controls the brake fluid pressure to reach the target slip rate.

Grip Force of Tire and Road Surface

COMPONENTS		MAIN FUNCTION
Wheel sensor		The wheel sensor outputs the speed signal to the ABS control unit according to the encoder's (pulser's) rotation speed.
Modulator- control unit	ABS control unit	The ABS control unit processes the signal from the wheel sensor, then outputs the ABS control signal to the modulator unit.
	Modulator unit	The modulator unit receives the control signal, then controls brake fluid pressure for each wheel.
Motor relay (inside of the ABS control unit)		The motor relay drives the ABS pump motor.
ABS fail-safe relay (inside of the ABS control unit)		The ABS fail-safe relay cuts the power to the solenoid valve when a problem is detected.

ABS Control Unit

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 transmits the control signal to the modulator unit solenoid valve when the slip rate is high.

The hydraulic control has three modes: pressure reducing, pressure retaining, and pressure intensifying.

Electronic Brake Distribution (EBD) Control

The electronic brake distribution (EBD) function helps control vehicle braking by adjusting the rear brake force before the ABS operates. Based on wheel sensor signals, the ABS control unit uses the modulator to control the rear brakes individually. When the rear wheel speed is less than the front wheel speed, the ABS control unit retains the current rear brake fluid pressure by closing the inlet valve in the modulator. As the rear wheel speed increases and approaches the front wheel speed, the control unit increases the rear brake fluid pressure by momentarily opening the inlet valve. This whole process is repeated very rapidly. While this is happening, there is kickback at the brake pedal.

During self-diagnosis, if the ABS control unit detects a problem that affects the EBD, it turns on the brake system indicator and the ABS indicator.

Self-diagnosis Function

1.	The ABS control unit is equipped with a CPU and a monitor IC. They check each other for problems.

2.	The CPU check the system circuits.

3.	The ABS control unit turns on the ABS and possibly the brake system indicator when the unit detects a problem, and the unit stops ABS operation.

4.	The self-diagnosis can be classified into these two categories: Initial diagnosis Regular diagnosis

On-board Diagnosis Function

The ABS can be diagnosed with the Honda PGM or HDS Tester.
The ALB Checker cannot be used with this system. For air bleeding, and checking wheel sensor signals, use the Honda PGM or HDS Tester. See the Honda PGM Tester user's manual or HDS help menu for specific operating instructions.

ABS Modulator

The ABS modulator consists of the inlet solenoid valve, outlet solenoid valve, reservoir, pump, and the pump motor. 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: normal braking, pressure retaining, and pressure reducing. The hydraulic circuit is an independent four channel type, one channel for each wheel.

Shown in normal braking mode

Normal braking 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 reducing mode:	Inlet valve closed, outlet valve open Caliper fluid flows through the outlet valve to the reservoir. When in pressure reducing mode, the pump motor is ON. The reservoir fluid is pumped out by the pump, through the damping chamber, to the master cylinder. When stopping ABS operation, the pump motor is OFF.

Wheel Sensors

The wheel sensors are the magnetic contactless type. The wheel sensors detect changing of magnetic polarity on the magnetic encoder contained inside the front wheel bearings. The ABS control unit calculates the wheel speed based on signals received from the wheel sensor.

NOTE: The front wheel bearings are directional.

Wheel Speed and Modulator Control

When the wheel speed drops sharply below the vehicle speed, 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.