2002 ISUZU AXIOM brake sensor

5A±3
BRAKE CONTROL SYSTEM
General Description
The Anti-lock Brake System (ABS) works on all four
wheels. A combination of wheel speed sensor and
Electronic Hydraulic Control Unit (EHCU) 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.
NOTE: The Electronic Hydraulic Control Unit (EHCU)
comprises the Hydraulic Unit (H/U) and the coil Integrated
Module.
C05RW004
Legend
(1) Electronic Line
(2) Hydraulic Line
(3) Hydraulic Unit (H/U)(4) Coil Integrated Module
(5) Front Wheel Speed Sensor
(6) Rear Wheel Speed Sensor
(7) Proportioning and Bypass (P&B) Valve

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
excessive wheel deceleration (imminent lockup), the first
step in the anti-lock sequence is to isolate the brake
pressure being applied by the brake pedal.
The microprocessor in the coil integrated module sends a
voltage to the coil to energize and close the isolation
valve. This prevents any additional fluid pressure applied
by the brake pedal from reaching the wheel. With the
isolation valves closed, unnecessary increase in the
brake pressure is prevented.
C05RW011
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±24BRAKE CONTROL SYSTEM
EHCU Connector Pin-out Checks

Disconnect Electronic Hydraulic Control Module.

Perform checks with high impedance digital
multimeter J-39200 or equivalent.
No.
Circuit to be TestedIgnition
Switch
PositionMultimeter
Scale/RangeMeasure
between Pin
NumberNominal ValueNote
1Power supplyOFF20DCV1 (C±5)
2 (C±5)11.5V to 14.5V
2Ignition enableOFF20DCV1 (C±6)
7 (C±6)0V to 0.1V
ON20DCV1 (C±6)
7 (C±6)11.5V to 14.5V
3Stoplamp switchOFF20DCV13 (C±6)
7 (C±6)10.5V to 14.5VPress brake pedal
4Ground connectionOFF200
7 (C±6)
GroundLess than 2

OFF1
2 (C±5)
GroundLess than 0.2

5FL speed sensorOFF2k
2 (C±6)
10 (C±6)2.0k
to 2.8k
Internal Resistance
OFF200k
2 (C±6)
7 (C±6)more than
100k
Insulation Resistance
OFF200mACV 2 (C±6)
10 (C±6)more than
200mVTurn wheel at 1RPS
6FR speed sensorOFF2k
3 (C±6)
11 (C±6)2.0k
to 2.8k
Internal Resistance
OFF200k
3 (C±6)
7 (C±6)more than
100k
Insulation Resistance
OFF200mACV 3 (C±6)
11 (C±6)more than
200mVTurn wheel at 1RPS
7RR speed sensorOFF2k
4 (C±6)
12 (C±6)1.2k
to 2.0k
Internal Resistance
OFF200k
4 (C±6)
7 (C±6)more than
100k
Insulation Resistance
OFF200mACV 4 (C±6)
12 (C±6)more than
200mVTurn wheel at 1RPS

5A±30BRAKE CONTROL SYSTEM
Symptom Diagnosis
The symptoms that cannot be indicated by warning light
can be divided in the following five categories:
1. ABS works frequently but vehicle does not
decelerate.
2. Uneven braking occurs while ABS works.
3. The wheels lock during braking.
4. Brake pedal feel is abnormal.
5. Braking sound (from EHCU) is heard while not
braking.
These are all attributed to problems which cannot be
detected by EHCU self-diagnosis. Use the customer
complaint and test to determine which symptom is
present. Then follow the appropriate flow chart listed
below.
NoSymptomDiagnostic Flow ChartsNo.Sym tomWithout TECH 2With TECH 2
1ABS works frequently but vehicle does not decelerate.Chart A-1Chart TA-1
2Uneven braking occurs while ABS works.Chart A-2Chart TA-2
3The wheels are locked.Chart A-3Chart TA-3
4Brake pedal feel is abnormal.Chart A-4Ð
5Braking sound (from EHCU) is heard while not braking. Chart A-5Chart TA-5
Chart A-1 ABS Works Frequently But Vehicle Does Not Decelerate
StepActionYe sNo
1Is braking force distribution normal between front and rear of
vehicle?
Go to Step 2
Repair brake
parts.
Go to
Step 7
2Are axle parts installed normally?
Go to Step 3
Repair axle parts.
Go to
Step 7
3Is there play in each or any wheel speed sensor?Repair wheel
speed sensor.
Go to
Step 7Go to Step 4
4Is there damage, or powdered iron sticking to each or any wheel
speed sensor/sensor ring?Replace or repair
sensor or sensor
ring.
Go to
Step 7Go to Step 5
5Is the output of each wheel speed sensor normal? (Refer to Chart
C-1 or TC-1
)
Go to Step 6
Replace wheel
speed sensor or
repair harness.
Go to
Step 7
6Is the input of TOD control unit normal?
Go to Step 7
Replace TOD
control unit or
repair harness.
Go to
Step 7
7Reconnect all components, ensure all components are properly
mounted.
Was this step finished?Repeat the ªBasic
diagnostic flow
chartº
Go to Step 7

5A±31
BRAKE CONTROL SYSTEM
Chart TA-1 ABS Works Frequently But Vehicle Does Not Decelerate (Use TECH 2)
StepActionYe sNo
11. Connect TECH 2.
2. Make sure of the output conditions of each sensor.
Is the output of each sensor normal?
Go to Step 2
Replace wheel
speed sensor.
Go to
Step 3
2Return to Chart A-1.
Was the Chart A-1 finished?
Go to Step 3Go to Step 2
3Reconnect all components, ensure all components are properly
mounted.
Was this step finished?Repeat the ªBasic
diagnostic flow
chartº
Go to Step 3
Chart A-2 Uneven Braking Occurs While ABS Works
StepActionYe sNo
1Is there play in each or any sensor?Repair.
Go to
Step 5Go to Step 2
2Damage or powdered iron sticking to each or any sensor/sensor
ring?Repair.
Go to
Step 5Go to Step 3
3Is the output of each sensor normal? (Refer to Chart C-1 or TC-1)
Go to Step 4
Replace sensor
or repair harness.
Go to
Step 5
4Is brake pipe connecting order correct?
Replace H/U.
Go to
Step 5
Reconnect brake
pipe correctly.
Go to
Step 5
5Reconnect all components, ensure all components are properly
mounted.
Was this step finished?Repeat the ªBasic
diagnostic flow
chartº
Go to Step 5
Chart TA-2 Uneven Braking Occurs While ABS Works (Use TECH 2)
StepActionYe sNo
11. Connect TECH 2.
2. Make sure of the output conditions of each sensor.
Is the output of each sensor normal?
Go to Step 2Go to Step 3
2Check piping by TECH 2 ACTUATOR TEST
Is the piping normal?Replace EHCU.
Go to
Step 4
Repair the pipe.
Go to
Step 4
3Repair and check the wheel speed sensor (Refer to Chart B-20 to
B-23 , C-1 or TC-1
).
Was the each chart finished?
Go to Step 4Go to Step 3
4Reconnect all components, ensure all components are properly
mounted.
Was this step finished?Repeat the ªBasic
diagnostic flow
chartº
Go to Step 4