light ISUZU TROOPER 1995 Repair Manual

4-WHEEL ANTILOCK BRAKE SYSTEM (ABS) 5A4-1
SECTION 5A4
'--' 4-WHEEL ANTILOCK BRAKE SYSTEM (ABS)
CAUTION
All
brake attaching fasteners are an important attaching part in that they could affect performance of
vital parts and systems, and/or could result in major repair expense. They must be replaced with one
of the same part number or with an equivalent part if replacement becomes necessary. Do not use
replacement parts
of lesser quality or substitute design. Torque values must be used as specified
during reassembly to assure proper retention of these parts.
CONTENTS
General Description .................... 5A4-3
System Components ................. 5A4-3
Electronic Brake
Control Module ·
(EBCM) .......................... 5A4-3
Hydraulic Unit ...................... 5A4-3
ABS Warning Light .................. 5A4-4
Wheel
Speed Sensor ................. 5A4-4
G-Sensor
........................... 5A4-4
Normal and Antilock Braking .......... 5A4-4
Brake Pedal Travel
................... 5A4-4
Abbreviation ........................ 5A4-4
Diagnosis
............................. 5A4-5
General
Information ................. 5A4-5
ABS
System Service Precautions ....... 5A4-5
Computer System Service
Precautions
....................... 5A4-5
General Service Precautions
........... 5A4-5
Note on lntermittents ................ 5A4-6
Test Driving ABS Complaint Vehicles ... 5A4-6
II ABS11 Warning Light ................ 5A4-6
Normal Operation ................... 5A4-6
Basic
Diagnostic Flow Chart ........... 5A4-7
Basic
Inspection Procedure ............ 5A4-8
TECH 1
TOOL. ......................... 5A4-10
1. What can be done with TECH 1 ...... 5A4-10
2. How to Use TECH 1 ................ 5A4-11
3. Explanation of Modes .............. 5A4-15
Mode FO: Data List ................... 5A4-16
Mode F2: Trouble Code ............... 5A4-18
Mode F3: Snapshot .................. 5A4-19
Mode F4: Clear Code ................. 5A4-20
Mode F5: Actuator Test ............... 5A4-21
Mode F6: Wheel Sensors ............. 5A4-31
Pin-Out Checks ........................ 5A4-33
Circuit Diagram ..................... 5A4-34
Part Location ....................... 5A4-37
Symptom Diagnosis .................... 5A4-38
CHART A-1 1) ABS Works Frequently
but Vehicle does not Decelerate ...... 5A4-39
CHART TA-1 1) ABS Works Frequently
but Vehicle does not Decelerate ...... 5A4-40
CHART A-2 2) Uneven Braking Occurs
while ABS Works .................. 5A4-41
CHART TA-2 2) Uneven Braking Occurs
while ABS Works .................. 5A4-42
CHART A-3, T A-3 3) The Wheels are
Locked
........................... 5A4-43
CHART A-4 4) Brake Pedal Feel is
Abnormal ........................ 5A4-44
CHART A-5 , T A-5 5) Braking Sound
(from Hydraulic Unit) is Heard while
not Braking ....................... 5A4-45
Diagnosis by 11 ABS11 Warning Light
Illumination Pattern .................. 5A4-46
Diagnostic Trouble Codes (DTCs) ....... 5A4-47
1. How to Display and Erase DTCs ... 5A4-47
2. Diagnostic Trouble Codes ........ 5A4-49
CHART B-1 With the Key in the ON
Position (before Starting the Engine),
Warning Light (W /L) is not
•
Actuated ........................ 5A4-50
CHART B-2 II ABSII Light Flashes
Twice with Key ON ................ 5A4-51
CHART B-3 EBCM Abnormality (Diagnostic
Trouble Code 14) .................. 5A4-52
CHART B-4 Power Voltage Drop (Diagnostic
Trouble Code 15) .................. 5A4-53
CHART B-5 G-Sensor Circuit (Diagnostic
Trouble Code 21) .................. 5A4-54
CHART B-6 Brake Switch Trouble
(Diagnostic Trouble Code 22) ........ 5A4-55
CHART B-7 Abnormal Transmission Input
(A/T Modei)(Diagnostic Trouble
Code 23) ......................... 5A4-56
CHART B-7 Abnormal Transmission Input
(M/T Modei)(Diagnostic Trouble
Code 23) ......................... 5A4-57
CHART B-8 Hydraulic Unit (HU) Pump
Motor and Motor Relay Circuit
(Diagnostic Trouble Code 32) ........ 5A4-58
CHART B-9 Solenoid Valve Abnormality
(Diagnostic Trouble Code 41, 42,
& 44) ............................ 5A4-59
CHART B-10 Valve Relay Abnormality
(Diagnostic Trouble Code 45) ........ 5A4-60

4-WHEEL ANTILOCK BRAKE SYSTEM (ABS) 5A4-3
GENERAL DESCRIPTION
The Antilock Brake System (ASS) works on all four
wheels. A combination of wheel speed sensor and
Electronic Brake Control Module (EBCM) can
determine
when a wheel is about to stop turning
and adjust brake pressure to maintain best braking.
This system
helps the driver maintain greater
control of the vehicle under heavy braking
conditions.
Master Cylinder
I I I I
--------Electric
===== Hydraulic
,--1 I
I
I
-ld4
1. Hydraulic unit 2. Electronic brake control module (EBCM)
3. Front wheel speed sensor 4. Rear wheel speed sensor
5. G-sensor 6. Proportioning and bypass (P&Bl valve
(Refer to "Hydraulic Brakes"(Sec. 5A).)
Fig. 5A4-1
SYSTEM COMPONENTS
The Antilock Brake System consists of a Hydraulic
Unit, Electronic Brake Control Module (EBCM), four
Wheel Speed Sensors, Warning Light, and G­
sensor.
ELECTRONIC BRAKE CONTROL MODULE
(EBCM)
The EBCM consists of ABS control circuits, fault
detector, and a fail-safe. It drives the hydraulic unit
according to the signal from each sensor,
cancelling ABS to return to normal braking when a
malfunction has occurred in the ABS.
The EBCM is self-diagnosing function can indicate
faulty circuits during diagnosis.
'--" HYDRAULIC UNIT
The hydraulic unit is mounted on the engine room
front right side. It consists of a Motor, Plunger
Pump, Solenoid Valves and Check Valve. On
the
outside, the relay box containing a motor
relay and a valve relay is installed.
Solenoid Valves;
Reduces or holds the calip~r fluid
pressure for each front disc brake or both rear disc
brakes according
to the signal sent from the EBCM.
Reservoir;
Temporarily holds the brake fluid that
returns from the front and rear disc brake caliper so
that pressure of front disc brake caliper can be
reduced
smoothly.
Plunger
Pump; Feeds the brake fluid held in the
reservoir
to the master cylinder.
Motor; Drives the pump according to the signal
from EBCM.
Check
Valve; Controls the brake fluid flow.

5A4-4 4-WHEEL ANTILOCK BRAKE SYSTEM (ABS)
ABS WARNING LIGHT
Vehicles equipped with the Antilock Brake System
have an
amber "ABS" warning light in the
instrument panel. The "ABS" warning light will
illuminate if a malfunction in the Antilock Brake
System is detected by the Electronic Brake
Control
Module (EBCM). In case of an electronic
malfunction, the EBCM will turn "ON" the "ABS"
warning light and disable the Antilock braking
function.
The
"ABS" 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.
If the "ABS" light stays "ON" after engine start-up,
or comes "ON" and stays "ON" while driving, the
Antilock Brake System should be inspected
for a
malfunction according to the diagnosis procedure.
Fig. 5A4-2
WHEEL SPEED SENSOR
It consists of a sensor and a rotor. The sensor is
attached
to the knuckle on the front wheels and to
the axle shaft bearing holder on the rear wheels.
The
rotor is press-fit in the axle shaft.
The
flux generated from electrodes magnetized by
a magnet in the sensor varies due to rotation of the
rotor, and the electromagnetic
induction generates
alternating voltage in
the coil. This voltage draws a
"sine curve" with the frequency proportional to
rotor speed and it allows detection of wheel speed.
G-SENSOR
The G-sensor installed inside the center console
detects the vehicle deceleration speed and sends a
signal
to the EBCM. It is normally on, and is turned
off when the vehicle deceleration speed exceeds
about 0.35G.
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 road surface is low or high, and changes the
EBCM's operating system to ensure ABS control.
NORMAL AND ANTILOCK BRAKING
Under normal driving conditions, the Antilock 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 antilock function or until the vehicle is
stopped. A
slight ticking or popping noise may be
heard
during brake applications when the Antilock
features is being used.
When the
Antilock 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.
BRAKE PEDAL TRAVEL
Vehicles equipped with the Antilock 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.
ABBREVIATIONS
Several abbreviations are commonly used
throughout this section:
ABS .......................................... Antilock Brake System
CKT ...................................................................... Circuit
DLC ............................................... Data Link Connector
EBCM ....................... Eiectronic Brake Control Module
FL. ................................................................... Front Left
FR ................................................................. Front Right
GEN ............................................................... Generator
HU .......................................................... Hydraulic Unit
MV ................................................................... Millivolts
RL .................................................................... Rear Left
RR ................................................................. Rear Right
RPS .......................................... Revolution per Second
UVR ............................................................. Valve Relay
VDC .................................................................. DC Volts
VAC .................................................................. AC Volts
W/L .........................................................
Warning Light
WSS ............................................ Wheel Speed Sensor

4-WHEEL ANTILOCK BRAKE SYSTEM (ABS) 5A4-5
DIAGNOSIS
GENERAL INFORMATION
ABS troubles can be classified to 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 5A, 5A1, 5A2, 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 SYSTEM 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.
PINOUT BOX
In order to prevent damage to the 35-pin Electronic
Brake
Control Module (EBCM) connector, J-35592
pinout box should be installed on the EBCM
connector prior to probing any circuit with the
digital
multimeter. This pinout box is to be used
combined with J-35616 connector test adapter kit.
W IMPORTANT
Do not probe the 35-pin EBCM connector
without installing J-35592 pinout box. Damage
to connector terminals may occur if the pinout
box is not installed, resulting in improper
system operation. The following procedure
should be used to install J-35592 pinout box.
1. Ignition must be "OFF" when installing or
removing the 35-pin EBCM connector.
Fig. 5A4-3
2. Disconnect the 35-pin EBCM harness connector
by depressing the connector locking plate and
rotating
the connector toward the front of
vehicle.
3. Inspect the 35-pin connector for damage.
Connect J-35592 to the 35-pin connector.
4. Proceed with test as outlined in the diagnostic
procedure.
J-39200 HIGH IMPEDANCE MUL TIMETER
When circuit measurements are requested, use a
circuit tester
with high impedance.
COMPUTER SYSTEM SERVICE
PRECAUTIONS
The Antilock Brake System interfaces directly with
the Electronic Brake Control Module (EBCM) 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
EBCM 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
Antilock Brake System and/or
other vehicle
systems. Failure
to observe these precautions may
result in Antilock Brake System damage.
If welding work is to be performed on the
vehicle using an electric arc welder, the EBCM
and valve block connectors should be
disconnected before the
welding operation
begins.
The
EBCM and valve block connectors should
never be connected or disconnected with the
ignition "ON".
Hydraulic units of the Antilock Brake System
are not separately serviceable and must be
replaced
as assemblies. Do not disassemble
any
component which is designated as non­
serviceable in
this Section.

5A4-6 4-WHEEL ANTILOCK BRAKE SYSTEM (ABS)
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
a
jumper cable. This is because the Antilock 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 (40A). 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:
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
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.
2. Start the vehicle and accelerate to 30 km/h (19
mph) or more.
3. Slowly brake and stop the vehicle completely.
4. Then restart the vehicle and accelerate to 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
theW/Lis 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 give a test drive on a wide, even
road
with a small traffic.
If an abnormality is detected, be sure to
suspend the test and start
trouble diagnosis at
once.
II ABS" WARNING LIGHT
When ABS trouble occurs to actuate "ABS"
warning light, the trouble code corresponding to
the trouble is stored in the EBCM. 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 EBCM
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 antilock braking is no longer
available. Power assisted braking without
antilock control is still available.
NORMAL OPERATION
II 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.
•

4-WHEEL ANTILOCK BRAKE SYSTEM (ABS) 5A4-7
BASIC DIAGNOSTIC FLOW CHART
I CUSTOMER COMPLAINT I
I
' I QUESTIONING TO CUSTOMER 1
I
BASIC INSPECTION I REFER TO "BASIC INSPECTION PROCEDURE"
+
I
I TECH 1 AVAILABLE I
I TECH 1 UNAVAILABLE REFER TO "DIAGNOSIS BY 'ABS'
t
WARNING LIGHT ILLUMINATION
PATTERN"
I MAKE SURE OF DTC BY I MODE F2: TROUBLE CODE I CHECK IF THE DTC IS STORED OR NOT
I I
I DTC I I NO DTC I I NO
DTC I
I DTC I
I I
I TEST
DRIVEl
I
I W/L NOT LIT I I W/L IS LIT I
I
I TROUBLE DIAGNOSIS I BASED ON SYMPTOM I LOCATING THE FAUL Tj BYDTC
REFER TO "SYMPTOM
DIAGNOSIS"
I REPAIR OF FAUL TV PART I
I
CHECK TRANSMISSION/TRANSFER~ INPUT (CHART C-3, C-4, TC-3, TC-4)
ELIMINATION
OF DTC I
I
INSPECTION OF "ABS" W/L ILLUMINATION
1 PATTERN WITH IGNITION SW "ON"
+ I TEST DRIVE ~ REPEAT THE DIAGNOSIS IF
THE SYMPTOM OR DTC
APPEARS AGAIN
I FINISHED I
DTC = Diagnostic Trouble Code

5A4-8 4-WHEEL ANTILOCK BRAKE SYSTEM (ABS)
BASIC INSPECTION PROCEDURE
1. Basic Inspection of Service Brake
VISUALL V CHECK PAD & ROTOR
2. Inspection of Transfer Switch
3. Ground Inspection
PUT THE KEY SWITCH ON AND
SHIFT T/F LEVER TO 4H
CHECK IF 4WD LIGHT IS LIT
VISUALL
V CHECK ASS-RELATED
GROUND POINTS
•

5A4-10 4-WHEEL ANTILOCK BRAKE SYSTEM (ABS)
TECH 1 TOOL
TECH 1 is an effective tool for the diagnosis of
electrical fault of Antilock Brake System (ASS) and
system check.
Although you can completely
diagnose the system without a TECH 1, using the
tool is quicker. In the following procedures, the
!TECH 11 symbol shows where the TECH 1 is used.
The
t::nettll symbol means the tool is not used.
1. WHAT CAN BE DONE WITH TECH 1
ON TECH 1
TECH 1 is a hand-held tester (Fig. 5A4-4).
Connected
to the Data Link Connector (DLC)
installed in the vehicle, it communicates with
ABS control unit (EBCM), thereby conducting
various diagnoses and tests.
Fig. 5A4-4
For this
vehicle, use ISUZU '90-'94
TRANSMISSION/ASS cartridge.
TECH 1 can check the following items:
(1) Input values of EBCM sensors and
switches, and
working conditions of
solenoid valves.
(2) Diagnostic Trouble Code (DTC) No.
(3) Incoming/outgoing data records.
(4) The function of ABS through the
operation
of the motor and solenoid
valves.
(5) Clearing DTCs stored in EBCM.
How to connect TECH 1 with the vehicle (Fig.
5A4·5, 5A4-6)
(1) Insert the program cartridge (TK02500B-1)
securely
into the TECH 1 main unit (J-38770-1).
(2) Attach the adapter to the cable.
(3) Plug the ISUZU 3-pin adapter (T A-02279-8) into
the adapter.
(4) Insert one end of the power plug into the TECH
1 and the other end into the cigarette lighter of
the vehicle.
The power plug may as well be coupled
directly
to the battery using the battery cable
adapter (J-38770-4).
(5) Turn the ignition key OFF, and connect TECH 1
with DLC (Orange colored).
Fig. 5A4-5
Data link Connector (Orange)
Fig. 5A4-6

ABS-2E
NO TROUBLE CODE
SELECT MODE
FO:DATA LIST
F1: NOT USED
F2:TROUBLE CODE
SELECT MODE
F3:SNAP SHOT
F4:CLEAR CODE
F5:ACTUATOR TEST
SELECT MODE
F6:WHEEL SENSORS
*note 1
ABS-2E
NO DATA!
CHECK ALDL CONN.
SEE CHART 1
4-WHEEL ANTILOCK BRAKE SYSTEM (ABS) 5A4-13
There is no trouble code in ABS system.
(In case of trouble, trouble code is displayed)
Select
desired mode (see following explanation of modes). (Scroll up and
down by key III. m operation.)
Chances are
that the picture as shown in the box appears next to the 8th
picture.
It is displayed when there is no communication between TECH 1
and the EBCM. The
following causes are considered:
CHART
1:
There are three different situations in which EBCM does not communicate
with TECH 1:
1) Disconnection of Data Link Connector (ALDL) Harness
Check
to see "ABS" warning light is normally actuated with IGN being
ON. lfthe light is not actuated, harness abnormality is suspected.
2) While driving (wheel speed values inputted)
No problem in running the vehicle after communicating with TECH 1
while the vehicle stops.

5A4-16 4-WHEEL ANTILOCK BRAKE SYSTEM (ABS)
MODE FO: DATA LIST (When connected (communication with EBCM) while warning light is
off)
The data displayed by MODE FO: OAT A LIST are as follows:
Display Content OK/NG Criteria for Data
FL WHEEL SPEED km/h (mph) • Start the vehicle and make sure of linear change in each
FR WHEEL SPEED wheel speed.
• Turn each wheel by hand and make sure that each speed RL WHEEL SPEED data changes.
RR WHEEL SPEED
UVR MONITOR
Voltage • About 5V with key ON
VALVE RELAY INACTIVE • ACTIVE with key ON
ACTIVE
Voltage •
About 5V with brake pedal
BRAKE SWITCH • About OV with brake pedal
released
OPEN (Released)
• CLOSE
with brake pressed
CLOSE (Pressed) • OPEN with brake pedal released
ABSWARNING ACTIVE
• To be ACTIVE usually
LIGHT
INACTIVE
WHL. SENSOR RES. FAULT • Normal, if OKAY
OKAY
-FL SOL. VALVE ACTIVE • To be INACTIVE usually
FR SOL. VALVE INACTIVE
REAR SOL. VALVE
P. MOTOR RELAY ACTIVE • To be INACTIVE usually
INACTIVE
OFF-ROAD-INPUT Voltage A/T 1 L, R: less than O.SV
Other: 3 ±O.SV
MIT 1, 2, R: more than 4.0V
Other:
3 ± O.SV
T/F SWITCH OPEN • 4WD: CLOSE
CLOSE •
2WD: OPEN
As for ABS vehicle speed unit, km/h and mph are displayed alternately through Key F7.
•