Isuzu KB P190. Manual — part 154

BRAKE CONTROL SYSTEM 5A-23

Electronic Brake-force Distribution (EBD) System

ABS has the EBD function. EBD is a function which
controls braking force distribution of a front wheel and a
rear wheel, and makes brake fluid pressure of a rear
wheel the optimal. If the rate of slip of a rear wheel
becomes greater compared to a front wheel, the brake
fluid pressure of a rear wheel will be controlled in order
to perform braking force distribution between the front
and rear wheels. EBD enables the braking power of a
rear wheel to always be utilized for the maximum
according to the load change concerning the back axis
according to the vehicle’s loading state (No luggage,
loading, etc.), deceleration, etc. Brake fluid pressure
control to a rear wheel is performed by the EBD function
which uses the ABS function without the mechanical
proportioning valve.

C05L300016

Brake Pedal Travel

Vehicles equipped with the Anti-lock Brake System may
be stopped by applying normal force to the brake pedal.
Although there is no need to push the pedal beyond the
point where it stops or holds the vehicle, by applying
more force the pedal will continue to travel toward the
floor.

This extra brake pedal travel is normal.

Acronyms and Abbreviations

Several acronyms and abbreviations are commonly
used throughout this section:

ABS

Anti-lock Brake System

CKT

Circuit

DLC

Data Link Connector

EBD

Electronic Brake-force Distribution

EHCU

Electronic Hydraulic Control Unit

FL

Front Left

FR

Front Right

GEN

Generator

H/U

Hydraulic Unit

MV

Millivolts

RR

Rear

RPS

Revolutions per Second

VDC

DC Volts

VAC

AC Volts

W/L

Warning Lamp

WSS

Wheel Speed Sensor

General Diagnosis

General Information

ABS problems can be classified into two types, those
which can be detected by the ABS warning lamp and
those which can be detected as a vehicle abnormality
by the driver.

In either case, locate the fault in accordance with the
“BASIC DIAGNOSTIC FLOWCHART” and repair.

Please refer to Section 5C for the diagnosis of
mechanical troubles such as brake noise, brake judder
(brake pedal or vehicle vibration felt when braking),
uneven braking, and parking brake trouble.

ABS Service Precautions

Required Tools and Items:

• Box Wrench

• Brake

Fluid

• Special Tool

Some diagnosis procedures in this section require the
installation of a special tool.

5-8840-0366-0 High Impedance Multimeter

When circuit measurements are requested, use a circuit
tester with high impedance.

5A-24 BRAKE CONTROL SYSTEM

Computer System Service Precautions

The Anti-lock Brake System and Electronic Brake-force
Distribution interfaces directly with the Electronic
Hydraulic Control Unit (EHCU) which is a control
computer that is similar in some regards to the Engine
Control Module. These modules are designed to
withstand normal current draws associated with vehicle
operation. However, care must be taken to avoid
overloading any of the EHCU circuits. In testing for
opens or shorts, do not ground or apply voltage to any
of the circuits unless instructed to do so by the
appropriate diagnostic procedure. These circuits should
only be tested with a high impedance multimeter
5-8840-0366-0 or special tools as described in this
section. Power should never be removed or applied to
any control module with the ignition in the “ON” position.

Before removing or connecting battery cables, fuses or
connectors, always turn the ignition switch to the “OFF”
position.

General Service Precautions

The following are general precautions which should be
observed when servicing and diagnosing the Anti-lock
Brake System and/or other vehicle systems. Failure to
observe these precautions may result in Anti-lock Brake
System and Electronic Brake-force Distribution
damage.

•

If welding work is to be performed on the vehicle
using an electric arc welder, the EHCU and valve
block connectors should be disconnected before the
welding operation begins.

•

The EHCU and valve block connectors should
never be connected or disconnected with the
ignition “ON”.

Note:

•

If only rear wheels are rotated using jacks or drum
tester, the system will diagnose a speed sensor
malfunction and the “ABS and Brake” warning lamp
will illuminate. But actually no trouble exists. When
the DTC is not detected and the ABS and BRAKE
warning lamp is on, “How to erase code” is
performed and an ABS and BRAKE warning lamp
are off.

If the battery has been discharged

The engine may stall if the battery has been completely
discharged and the engine is started via jumper cables.
This is because the Anti-lock Brake System (ABS) and
Electronic Brake-force Distribution (EBD) System
requires a large quantity of electricity. In this case, wait
until the battery is recharged, or set the ABS and EBD
to a non-operative state by removing the fuse for the
ABS. After the battery has been recharged, stop the
engine and install the ABS fuse. Start the engine again,
and confirm that the ABS warning Lamp does not light.

Note on Intermittents

As with virtually any electronic system, it is difficult to
identify an intermittent failure. In such a case duplicating
the system malfunction during a test drive or a good
description of vehicle behavior from the customer may
be helpful in locating a “most likely” failed component or
circuit. The symptom diagnosis chart may also be
useful in isolating the failure. Most intermittent
problems are caused by faulty electrical connections or
wiring. When an intermittent failure is encountered,
check suspect circuits for:

•

Suspected harness damage.

•

Poor mating of connector halves or terminals not
fully seated in the connector body (backed out).

•

Improperly formed or damaged terminals.

Test Driving ABS Complaint Vehicles

If there has been an abnormality in the lighting pattern
of the “ABS” warning lamp, the fault can be located in
accordance with the “DIAGNOSIS BY “ABS” WARNING
LAMP ILLUMINATION PATTERN”. Although such
problems can be detected by the driver as a vehicle
symptom, it is still necessary to perform a test drive
following the test procedure mentioned below, in order
to reproduce the symptom for problem diagnosis on a
symptom basis:

1. Start the engine and make sure that the “ABS” W/L

goes OFF. If the W/L remains ON, it means that
the Diagnostic Trouble Code (DTC) is stored.
Therefore, read the code and locate the fault.

Note: The DTC cannot be cleared if the vehicle speed
does not exceed about 10km/h (6mph) at DTC, even
though the repair operation is completed.

2. Start the vehicle and accelerate to about 30 km/h

(19 mph) or more.

3. Slowly brake and stop the vehicle completely.

4. Then restart the vehicle and accelerate to about 40

km/h (25 mph) or more.

5. Brake at a time so as to actuate the ABS and stop

the vehicle.

6. Be cautious of abnormality during the test. If the

W/L is actuated while driving, read the DTC and
locate the fault.

7. If the abnormality is not reproduced by the test,

make best efforts to reproduce the situation
reported by the customer.

8. If the abnormality has been detected, repair in

accordance with the “SYMPTOM DIAGNOSIS”.

Note:

•

Be sure to perform a test drive on a wide, even road
with light traffic.

•

If an abnormality is detected, be sure to suspend
the test and start trouble diagnosis at once.

BRAKE CONTROL SYSTEM 5A-25

“ABS” Warning Lamp

When ABS and problems occur that actuate the “ABS”
warning lamp, the code corresponding to the problem is
stored in the EHCU. Only ordinary braking is available
when the ABS is deactivated. Even when the “ABS”
warning lamp is actuated, if the starter switch is set ON
after setting it OFF once, the EHCU checks up on the
entire system. If there is no abnormality, the EHCU
judges ABS to work correctly and the warning lamp is lit
normally, even though the problem code is stored.

NOTE: Illumination of the “ABS” warning lamp indicates
that anti-lock braking is no longer available. Power
assisted braking without anti-lock control is still
available.

Normal Operation

“ABS ” Warning Lamp

When the ignition is first moved from “OFF” to “RUN”,
the amber “ABS” warning lamp will turn “ON”. The
“ABS” warning lamp will turn “ON” during engine
starting and will usually stay “ON” for approximately
three seconds after the ignition switch is returned to the
“ON” position. The warning lamp should remain “OFF”
at all other times.

Brake (EBD) Warning Lamp

RTW75ASH000101

Vehicles equipped with the EBD (Electronic Brake-force
Distribution) System have a “Brake” warning lamp on
the instrument panel.

If the ABS warning lamp and Brake warning lamp are
turned "ON", then EBD has failed. ( Parking brake
switch is "OFF")

In the following conditions, the EBD warning lamp is
"ON".

•

Starter switch is "ON", engine "OFF".
( Parking brake switch is "OFF")

If engine is started, then EBD warning lamp is "OFF".
( Parking brake switch is "OFF")

5A-26 BRAKE CONTROL SYSTEM

Tech 2 Scan Tool

Operating Procedure

The power up screen is displayed when you power
up the tester with the systems PCMCIA card. Follow
the operating procedure below.

060R100102