Isuzu Rodeo UE. Service manual — part 97

5A–11

BRAKE CONTROL SYSTEM

DLC
Data Link Connector

EHCU
Electronic Hydraulic Control Unit

FL
Front Left

FR
Front Right

GEN
Generator

H/U
Hydraulic Unit

MV
Millivolts

RR
Rear

RPS
Revolution per Second

VDC
DC Volts

VAC
AC Volts

W/L
Warning Light

WSS
Wheel Speed Sensor

General Diagnosis

General Information

ABS troubles can be classified into two types, those
which can be detected by the ABS warning light 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:

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Box Wrench

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Brake Fluid

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Special Tool

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

J-39200 High Impedance Multimeter
When circuit measurements are requested, use a circuit
tester with high impedance.

Computer System Service Precautions

The Anti-lock Brake System interfaces directly with the
Electronic Hydraulic Control Unit (EHCU) which is a
control computer that is similar in some regards to the

Powertrain 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 (J-39200) 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 damage.

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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.

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

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If only rear wheels are rotated using jacks or drum
tester, the system will diagnose a speed sensor
malfunction and the “ABS” warning light will
illuminate. But actually no trouble exists. After
inspection stop the engine once and re-start it, then
make sure that the “ABS” warning light does not
illuminate.

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)
requires a large quantity of electricity. In this case, wait
until the battery is recharged, or set the ABS to a
non-operative state by removing the fuse for the ABS
(60A). After the battery has been recharged, stop the
engine and install the ABS fuse. Start the engine again,
and confirm that the ABS warning light 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:

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Suspected harness damage.

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

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Improperly formed or damaged terminals.

5A–12

BRAKE CONTROL SYSTEM

Test Driving ABS Complaint Vehicles

In case that there has been an abnormality in the lighting
pattern of “ABS” warning light, the fault can be located in
accordance with the “DIAGNOSIS BY “ABS” WARNING
LIGHT ILLUMINATION PATTERN” . In case of such
trouble as can be detected by the driver as a vehicle
symptom, however, it is necessary to give a test drive
following the test procedure mentioned below, thereby
reproducing the symptom for trouble 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 12 km/h (8 mph) 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:

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Be sure to give a test drive on a wide, even road with a
small traffic.

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

“ABS” Warning Light

When ABS trouble occurs to actuate “ABS” warning light,
the trouble code corresponding to the trouble is stored in
the EHCU. Only ordinary brake is available with ABS
being unactuated. Even when “ABS” warning light is
actuated, if the starter switch is set ON after setting it OFF
once, the EHCU checks up on the entire system and, if
there is no abnormality, judges ABS to work currently and
the warning light is lit normally even though the trouble
code is stored.

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

Normal Operation

“ABS” Warning Light
When the ignition is first moved from “OFF” to “RUN” , the
amber “ABS” warning light will turn “ON” . The “ABS”
warning light 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 light should remain “OFF” at all other times.

5A–13

BRAKE CONTROL SYSTEM

Tech 2 Scan Tool

From 98 MY, Isuzu dealer service departments are
recommended to use Tech 2. Please refer to Tech 2 scan
tool user guide.

901RW257

Legend

(1) PCMCIA Card
(2) SAE 16/19 Adaptor

(3) DLC Cable
(4) Tech–2

5A–14

BRAKE CONTROL SYSTEM

Getting Started

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Before operating the Isuzu PCMCIA card with the
Tech 2, the following steps must be performed:

1. The Isuzu 98 System PCMCIA card (1) inserts into

the Tech 2 (4).

2. Connect the SAE 16/19 adapter (2) to the DLC cable

(3).

3. Connect the DLC cable to the Tech 2 (4).
4. Make sure the vehicle ignition is off.
5. Connect the Tech 2 SAE 16/19 adapter to the vehicle

DLC.

740RW060

6. The vehicle ignition turns on.
7. Power up the Tech 2.
8. Verify the Tech 2 power up display.

060RW009

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

060RX065