Isuzu KB P190. Manual — part 153

BRAKE CONTROL SYSTEM 5A-19

Parts Location (LHD) (2)

RTW78AXF047001

5A-20 BRAKE CONTROL SYSTEM

EHCU Pin-Assignment

RTW75ASF000101

EHCU Side

Pin No.

Pin Function

Wire Color

Typical Value

Note

1 Ground

1

BLK

0V

(Less than 0.1V)

Motor

2

Power Supply

WHT/RED

Battery Voltage

Motor

3

Power Supply

WHT/GRN

Battery Voltage

Solenoid

4 Ground

2

BLK

0V

(Less than 0.1V)

Solenoid,

Control Unit

5

Front Left Wheel Speed Sensor (-)

WHT

High Level: 0.8~1.3V

Low Level: 0.4~0.7V

DTC C0225, C0226

6

Rear Left Wheel Speed Sensor (+)

WHT/BLU

12±1.5V

DTC C0235, C0236

7

Rear Right Wheel Speed Sensor (+)

ORN

12±1.5V

DTC C0231, C0232

8

Rear Right Wheel Speed Sensor (-)

BLK

High Level: 0.8~1.3V

Low Level: 0.4~0.7V

DTC C0231, C0232

9

Front Right Wheel Speed Sensor (+)

BRN

12±1.5V

DTC C0221, C0222

10

Front Right Wheel Speed Sensor (-)

LT

GRN/BLK

High Level: 0.8~1.3V

Low Level: 0.4~0.7V

DTC C0221, C0222

11 Serial

VIO/GRN

-

Keyword

2000

12

EBD (Brake) Warning Lamp

LT BLU

More than 10V

-

13 Not

Used -

-

-

14

G Sensor Ground

YEL/GRN

0V

(Less than 0.1V)

4WD Only

DTC C0276, C0285

15 Not

Used -

-

-

16

Front Left Wheel Speed Sensor (+)

RED

12±1.5V

DTC C0225, C0226

17

Rear Left Wheel Speed Sensor (-)

WHT/BLU

High Level: 0.8~1.3V

Low Level: 0.4~0.7V

DTC C0235, C0236

18

Starter Switch ON

(Power Supply and Switch Position)

BLU/WHT

Battery Voltage

Control Unit

DTC C0277, C0278

19 Not

Used -

-

-

BRAKE CONTROL SYSTEM 5A-21

EHCU Side

Pin No.

Pin Function

Wire Color

Typical Value

Note

20

Stop Light Switch

RED

Open: 0V

Close: Battery Voltage

Close Condition:

Step on the Brake
Pedal

21

G Sensor Signal

YEL/BLK

2.0~3.0V

(MAX 4.0V, MIN 1.0V)

4WD Only

It checks in a flat place
(0G: 2.5V)

DTC C0276, C0285

22

ABS Warning Lamp

YEL

More than 10V

-

23 Not

Used -

-

-

24

Transfer (2-4WD Control Unit)

GRY

Pulse Signal

(High 4.5V, Low 1.5V)

4WD Only

DTC C0282

25

Serial

ORN/WHT

-

Short to GND:

Flash out DTCs

26 Not

Used -

-

-

5A-22 BRAKE CONTROL SYSTEM

System Components

Electronic Hydraulic Control Unit (EHCU), four Wheel
Speed Sensors, two Warning Lamps, and G sensor.

Electronic Hydraulic Control Unit (EHCU)

The EHCU consists of ABS control circuits, fault
detector, and a fail-safe. It drives the EHCU according
to the signal from each sensor, cancelling ABS to return
to normal braking when a malfunction has occurred in
the ABS.

The EHCU has a self-diagnosing function which can
indicate faulty circuits during diagnosis.

The EHCU is mounted on the engine compartment rear
left side. It consists of a motor, solenoid valves and a
fail safe relay.

Solenoid Valves: Reduces or holds the caliper fluid
pressure for each front brake or both rear brakes
according to the signal sent from the EHCU.

Buffer chamber: Temporarily holds the brake fluid that
returns from the front and rear brake so that pressure of
front brake can be reduced smoothly.

Motor: Drives the pump according to the signal from
EHCU.

Fail safe Relay: When failure occurs in ABS.

The power supply to solenoid Valve is cut.

ABS Warning Lamp

RTW75ASH000101

Vehicles equipped with the Anti-lock Brake System
have an amber “ABS” warning lamp on the instrument
panel. The “ABS” warning lamp will illuminate if a
malfunction in the Anti-lock Brake System is detected
by the Electronic Hydraulic Control Unit (EHCU). In the
case of an electronic malfunction, the EHCU will turn
“ON” the “ABS” warning lamp and disable the anti-lock
braking function.

The “ABS” warning lamp will turn “ON” for
approximately three seconds after the ignition switch is
in the “ON” position.

If the “ABS” warning lamp stays “ON” after the ignition
switch is in the “ON” position, or comes “ON” and stays
“ON” while driving, the Anti-lock Brake System should
be inspected for a malfunction according to the
diagnostic procedure.

Wheel Speed Sensor (WSS)

It consists of a sensor and a rotor. The sensor is
attached to the knuckle on the front wheels and to the
rear wheels.

The rotor is press-fit in the axle shaft.

G Sensor

The G sensor detects the vehicle deceleration speed
and sends a signal to the EHCU. In 4WD operation, all
four wheels may be decelerated in almost the same
phase, since all wheels are connected mechanically.

This tendency is noticeable, particularly on roads with
low friction coefficient, and the ABS control is adversely
affected.

The G sensor judges whether the friction coefficient of
the road surface is low or high, and changes the
EHCU's operating system to ensure ABS and EBD
control.

Normal and Anti-lock Braking

Under normal driving conditions, the Anti-lock Brake
System functions the same as a standard power
assisted brake system. However, with the detection of
wheel lock-up, a slight bump or kick-back will be felt in
the brake pedal. This pedal “bump” will be followed by a
series of short pedal pulsations which occurs in rapid
succession. The brake pedal pulsation will continue
until there is no longer a need for the anti-lock function
or until the vehicle is stopped. A slight ticking or popping
noise may be heard during brake applications when the
anti-lock feature is being used.

When the anti-lock feature is being used, the brake
pedal may rise even as the brakes are being applied.
This is also normal. Maintaining a constant force on the
pedal will provide the shortest stopping distance.