2002 ISUZU AXIOM Brake fluid

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 pressure into a low
pressure accumulator.
The microprocessor activates the normally closed dump
valve to open, allowing fluid from the wheels to be
dumped into the accumulator. This is done with very short
activation pulses opening and closing the dump valve
passageway. Brake pressure is reduced at the wheel and
allows the wheel to begin rotating again. The fluid from the
brake piston is stored in the accumulator against spring
pressure and a portion of this fluid also primes the pump.
The dump valves are operated independently to control
the deceleration of the wheel.
C05RW009
Legend
(1) Brake
(2) Master Cylinder

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 pressure to reach the
brakes. This controlled pressure rise continues until the
wheel is at optimum brake output or until the brake
pressure is brought up to the master cylinder output
pressure.
If more pressure is required, more fluid is drawn from the
master cylinder and applied to the brakes. The driver may
feel slight pedal pulsations, or pedal drop, this is normal
and expected.As fluid is re-applied to the brakes, the wheel speed will
reduce. If the wheels approach imminent lockup again,
the module will isolate, dump and re-apply again. This
cycle occurs in millisecond intervals, allowing several
cycles to occur each second. It is a much faster and more
controlled way of ªpumping the pedalº.
C05RW014
Legend
(1) Brake
(2) Master Cylinder

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. As this fluid
returns into the system, the spring forces the piston back
to its original position.
The isolation valve opens and fluid may return to the
master cylinder. Conventional braking is then resumed.
C05RW013
Legend
(1) Brake
(2) Master Cylinder

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.

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

5A±16BRAKE CONTROL SYSTEM
DATA LIST
The data displayed by DATA LIST are as follows:
Display
ContentOK/NG Criteria for Data
Front Left Wheel Speed
Front Right Wheel Speed
Rear Wheel Speedskm/h (MPH)
Start the vehicle and make sure of linear change in
each wheel speed.

Turn each wheel by hand and make sure that each
speed data change.
Warning LampON/OFF
To be OFF usually
ABS StateON/OFF
To be OFF usually
ABS RelayActive/Inactive
To be Active usually
4 Wheel DriveActive/Inactive
2WD: Inactive

4WD: Active
Brake SwitchActive/Inactive
Inactive (Released)

Active (Pressed)
Brake Fluid LevelNormal or not
To be Normal usually
Return PumpActive/Inactive
To be Inactive usually
DRP (Dynamic Rear
Proportioning)Active/Inactive
To be Inactive usually
Rear Dump Valve CommandedActive/Inactive
To be Inactive usually
Rear Dump Valve Feedback
Rear Isolation Valve
Commanded
Rear Isolation Valve Feedback
FL Dump Valve CommandedActive/Inactive
To be Inactive usually
FL Dump Valve Feedback
FL Isolation Valve Commanded
FL Isolation Valve Feedback
FR Dump Valve CommandedActive/Inactive
To be Inactive usually
FR Dump Valve Feedback
FR Isolation Valve
Commanded
FR Isolation Valve Feedback
G±SensorVoltage
2.50V when vehicle is stopped
Battery VoltageVoltage
Between 10±16.9V

5A±23
BRAKE CONTROL SYSTEM
Basic Inspection Procedure
1. Basic Inspection of Service Brake
StepActionYe sNo
1Is the fluid level normal?
Go to Step 2
Replenish with
fluid
Go to
Step 2
2Does fluid leak?Repair
Go to
Step 3Go to Step 3
3Is the booster functioning properly?
Go to Step 4
Repair
Go to
Step 4
4Is the pad and rotor within specs?
Go to Step 5
Repair
Go to
Step 5
5Reconnect all components. Ensure all component are properly
mounted.
Was this step finished?
FinishedGo to Step 5
2. Ground Inspection
StepActionYe sNo
1Is there good contact with the ABS ground points?
Go to Step 2
Repair
Go to
Step 2
2Reconnect all components. Ensure that all component are
properly mounted.
FinishedGo to Step 2

5C±1 POWER±ASSISTED BRAKE SYSTEM
AXIOM (Vehicles Produced Before July/31/2001)
BRAKES
POWER-ASSISTED BRAKE SYSTEM
CONTENTS
Service Precaution 5C±2. . . . . . . . . . . . . . . . . . . . . .
General Description 5C±2. . . . . . . . . . . . . . . . . . . . .
Diagnosis 5C±6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
General Diagnosis 5C±7. . . . . . . . . . . . . . . . . . . . . . .
Hydraulic Brakes 5C±10. . . . . . . . . . . . . . . . . . . . . . . .
Filling Master Cylinder Reservoir 5C±10. . . . . . . .
Deterioration of Brake Fluid 5C±10. . . . . . . . . . . . .
Leakage of Brake Fluid 5C±10. . . . . . . . . . . . . . . . .
Bleeding Brake Hydraulic System 5C±10. . . . . . . .
Flushing Brake Hydraulic System 5C±11. . . . . . . .
Brake Pipes and Hoses 5C±11. . . . . . . . . . . . . . . .
Brake Hose Inspection 5C±11. . . . . . . . . . . . . . . . .
Front Caliper Brake Hose 5C±12. . . . . . . . . . . . . . . .
Front Caliper Brake Hose and Associated
Parts 5C±12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Removal 5C±12. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 5C±12. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Rear Axle Brake Hose 5C±13. . . . . . . . . . . . . . . . . . .
Rear Axle Brake Hose and Associated
Parts 5C±13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Removal 5C±13. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 5C±13. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Brake Pipe 5C±14. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Removal 5C±14. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 5C±14. . . . . . . . . . . . . . . . . . . . . . . . . . . .
P & B (Proportioning and Bypass) Valve 5C±15. . . .
P & B (Proportioning and Bypass) Valve
Sectional View 5C±15. . . . . . . . . . . . . . . . . . . . . . . .
Removal 5C±15. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 5C±15. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Main Data and Specifications 5C±16. . . . . . . . . . . . .
Brake Pedal 5C±17. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Checking Pedal Height 5C±17. . . . . . . . . . . . . . . . .
Checking Pedal Travel 5C±17. . . . . . . . . . . . . . . . .
Brake Pedal and Associated Parts 5C±18. . . . . . .
Removal 5C±18. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 5C±18. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stoplight Switch 5C±19. . . . . . . . . . . . . . . . . . . . . . . . .
Parts Location 5C±19. . . . . . . . . . . . . . . . . . . . . . . .
Removal 5C±19. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 5C±19. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Main Data and Specifications 5C±20. . . . . . . . . . . . .
Fluid Reservoir Tank 5C±21. . . . . . . . . . . . . . . . . . . . .
Fluid Reservoir Tank and Associated Parts 5C±21Removal 5C±21. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 5C±21. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Master Cylinder Assembly 5C±22. . . . . . . . . . . . . . . .
Master Cylinder Assembly and Associated
Parts 5C±22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Removal 5C±22. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Inspection and Repair 5C±22. . . . . . . . . . . . . . . . . .
Installation 5C±23. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Main Data and Specifications 5C±24. . . . . . . . . . .
Special Tools 5C±24. . . . . . . . . . . . . . . . . . . . . . . . . .
Vacuum Booster Assembly 5C±25. . . . . . . . . . . . . . .
Vacuum Booster Assembly and Associated
Parts 5C±25. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Removal 5C±25. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Inspection and Repair 5C±26. . . . . . . . . . . . . . . . . .
Installation 5C±26. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Exterior Components 5C±28. . . . . . . . . . . . . . . . . . . .
Exterior Components and Associated Parts 5C±28
Removal 5C±28. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Inspection and Repair 5C±29. . . . . . . . . . . . . . . . . .
Installation 5C±29. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Vacuum Booster Overhaul 5C±29. . . . . . . . . . . . . . . .
Vacuum Booster 5C±29. . . . . . . . . . . . . . . . . . . . . . .
Main Data and Specifications 5C±30. . . . . . . . . . . . .
Special Tools 5C±31. . . . . . . . . . . . . . . . . . . . . . . . . . .
Front Disc Brake Pads 5C±32. . . . . . . . . . . . . . . . . . .
Front Disc Brake Pads Inspection 5C±32. . . . . . . .
Front Disc Brake Pads and Associated
Parts 5C±32. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Removal 5C±33. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 5C±33. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Front Disc Brake Rotor 5C±35. . . . . . . . . . . . . . . . . . .
Inspection 5C±35. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Replacing Brake Rotors 5C±35. . . . . . . . . . . . . . . .
Refinishing Brake Rotors 5C±35. . . . . . . . . . . . . . .
Front Disc Brake Caliper Assembly 5C±36. . . . . . . .
Front Disc Brake Caliper Assembly and
Associated Parts 5C±36. . . . . . . . . . . . . . . . . . . . . .
Removal 5C±37. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 5C±37. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Front Disc Brake Caliper 5C±39. . . . . . . . . . . . . . . . .
Front Disc Brake Caliper Disassembled
View 5C±39. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Disassembly 5C±39. . . . . . . . . . . . . . . . . . . . . . . . . .