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