Isuzu Rodeo UE. Manual - part 96

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. At this point, the brake
pedal is isolated from the base brake system, the
hydraulic control unit pumps are primed and the
attenuators are ready to pump fluid.

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Legend

(1) Brake
(2) Master Cylinder

5A–8

BRAKE 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 “pumping the pedal”.

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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.

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Legend

(1) Brake
(2) Master Cylinder

5A–10

BRAKE 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.  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 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

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Vehicles equipped with the Anti-lock Brake System have
an amber “ABS” warning light in the instrument panel.
The “ABS” 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 “ON” the “ABS” warning
light and disable the Anti-lock braking function.
The “ABS” light will turn “ON” for approximately three
seconds after the ignition switch is to the “ON” position.
If the “ABS” light stays “ON” after the ignition switch is the
“ON” position, or comes “ON” and stays “ON” 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 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 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 “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 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.

Acronyms and Abbreviations

Several acronyms and abbreviations are commonly used
throughout this section:

ABS
Anti-lock Brake System

CIM
Coil Integrated Module

CKT
Circuit