2002 ISUZU AXIOM Service Repair Manual

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Page 625 of 2100

ISUZU AXIOM 2002 Service Repair Manual 5A±6BRAKE CONTROL SYSTEM
Pressure Isolation (Pressure Maintain)
The electro-hydraulic control unit is activated when the
brakes are applied.
If the information from the wheel speed sensors indicates

Page 626 of 2100

ISUZU AXIOM 2002 Service Repair Manual 5A±7
BRAKE CONTROL SYSTEM
Pressure Reduction
Once the brake pressure is isolated, it must be reduced to
allow the wheels to unlock. This is accomplished by
dumping a portion of the brake fluid pressu

Page 627 of 2100

ISUZU AXIOM 2002 Service Repair Manual 5A±8BRAKE CONTROL SYSTEM
Pressure Increase (Re-apply)
The re-apply sequence is initiated to achieve optimum
braking. The isolation valve is momentarily opened to
allow master cylinder and pump pressu

Page 628 of 2100

ISUZU AXIOM 2002 Service Repair Manual 5A±9
BRAKE CONTROL SYSTEM
Brake Release
At the end of the anti-lock stop, when the brake pedal is
released, the pump will remain running for a short time to
help drain any fluid from the accumulators

Page 629 of 2100

ISUZU AXIOM 2002 Service Repair Manual 5A±10BRAKE CONTROL SYSTEM
System Components
Electronic Hydraulic Control Unit (EHCU), three Wheel
Speed Sensors, Warning Light, and G-sensor.
Electronic Hydraulic Control Unit (EHCU)
The EHCU consist

5A±10BRAKE CONTROL SYSTEM
System Components
Electronic Hydraulic Control Unit (EHCU), three Wheel
Speed Sensors, Warning Light, and G-sensor.
Electronic Hydraulic Control Unit (EHCU)
The EHCU consists of ABS control circuits, fault detector,
and a fail-safe. The signal received from each sensor
activates the hydraulic unit accordingly and cancels the
ABS to return to normal braking if a malfunction occurs in
the ABS system.
The EHCU has a self-diagnosing function which can
indicate faulty circuits during diagnosis.
The EHCU is mounted on the engine compartment rear
right side. It consists of a Motor, Plunger Pump, Solenoid
Valves.
Solenoid Valves: Reduces or holds the caliper fluid
pressure for each front disc brake or both rear disc brakes
according to the signal sent from the EHCU.
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
EHCU.
Check Valve: Controls the brake fluid flow.
ABS Warning Light
821R200015Vehicles equipped with the Anti-lock Brake System have
an amber ªABSº warning light in the instrument panel.
The ªABSº warning light will illuminate if a malfunction in
the Anti-lock Brake System is detected by the Electronic
Hydraulic Control Unit (EHCU).In case of an electronic
malfunction, the EHCU will turn ªONº the ªABSº warning
light and disable the Anti-lock braking function.
The ªABSº light will turn ªONº for approximately three
seconds after the ignition switch is turned to the ªONº
position.If the ªABSº light stays ªONº after the ignition switch is
turned to the ªONº position, or comes ªONº and stays
ªONº while driving, the Anti-lock Brake System should be
inspected for a malfunction according to the diagnosis
procedure.
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 rear axle
case on the rear differential.
The front sensor rotor is attached to the each brake rotor
by bolts.
The rear rotor is press-fit in the differential case.
The magnetic 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 ªsine
curveº with the frequency proportional to rotor speed and
it allows detection of wheel speed.
G-Sensor
The G-sensor installed inside the EHCU 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
road surface is low or high, and changes the EHCU's
operating system to ensure ABS 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 ªbumpº 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 features 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.
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.

Page 630 of 2100

ISUZU AXIOM 2002 Service Repair Manual 5A±11
BRAKE CONTROL SYSTEM
Acronyms and Abbreviations
Several acronyms and abbreviations are commonly used
throughout this section:
ABS
Anti-lock Brake System
CIM
Coil Integrated Module
CKT
Circuit
D

5A±11
BRAKE CONTROL SYSTEM
Acronyms and Abbreviations
Several acronyms and abbreviations are commonly used
throughout this section:
ABS
Anti-lock Brake System
CIM
Coil Integrated Module
CKT
Circuit
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
VA C
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
ªBASIC DIAGNOSTIC FLOWCHARTº 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 ToolSome 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 ªONº position.
Before removing or connecting battery cables, fuses or
connectors, always turn the ignition switch to the ªOFFº
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.
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 ªONº .
If only the rear wheels are rotated using jacks or drum
tester, the system will diagnose a speed sensor
malfunction and the ªABSº warning light will
illuminate. But actually no trouble exists. After
inspection stop the engine once and re-start it, then
make sure that the ªABSº 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
(50A). 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 ªmost likelyº failed component or

Page 631 of 2100

ISUZU AXIOM 2002 Service Repair Manual 5A±12BRAKE CONTROL SYSTEM
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 i

5A±12BRAKE CONTROL SYSTEM
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 suspected
circuits for damage:
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 of an intermittent ABS lamp illumination, see
ªDiagnosis by ABS Warning Light illumination Patternº or
go to 5A±37. In some cases, the vehicle may need to be
test driven by following the test procedure below.
1. Start the engine and make sure that the ªABSº 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 ªSYMPTOM DIAGNOSISº .
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.
ªABSº Warning Light
When ABS trouble occurs to actuate ªABSº 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 ªABSº 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 ªABSº warning light indicates
that anti-lock braking is no longer available. Power
assisted braking without anti-lock control is still available.
Normal Operation
ªABSº Warning Light
When the ignition is first moved from ªOFFº to ªRUNº , the
amber ªABSº warning light will turn ªONº . The ªABSº
warning light will turn ªONº during engine starting and will
usually stay ªONº for approximately three seconds after
the ignition switch is returned to the ªONº position. The
warning light should remain ªOFFº at all other times.

Page 632 of 2100

ISUZU AXIOM 2002 Service Repair Manual 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

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