2007 ISUZU KB P190 brake fluid

BRAKE CONTROL SYSTEM 5A-7
Normal Braking
During normal (non anti-lock) braking, the solenoid
valve has current flow.
Brake fluid travels through the center of the inlet valve
around the outlet valve then to the brake pistons.

RTW 75AMF000201
Legend
(1) Master Cylinder (5) Brake
(2) Brake Pedal (6) Outlet Valve
(3) Motor and Pump (7)Inlet Valve
(4) Accumulator



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ISUZU KB P190 2007

5A-8 BRAKE CONTROL SYSTEM
Pressure Isolation (Pressure Maintain)
The electronic-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 Control Unit sends a voltage
to the coil to energize and close the outlet valve. This
prevents any additional fluid pressure applied by the
brake pedal from reaching the wheel. W ith the outlet
valves closed, unnecessary increase in the brake
pressure is prevented.

RTW 75AMF000301
Legend
(1) Master Cylinder (5) Brake
(2) Brake Pedal (6) Outlet Valve
(3) Motor and Pump (7)Inlet Valve
(4) Accumulator



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ISUZU KB P190 2007

BRAKE CONTROL SYSTEM 5A-9
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 the
accumulator.
The microprocessor activates the normally closed outlet
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 outlet 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 outlet valves are operated independently to control
the deceleration of the wheel.

RTW 75AMF000401
Legend
(1) Master Cylinder (5) Brake
(2) Brake Pedal (6) Outlet Valve
(3) Motor and Pump (7)Inlet Valve
(4) Accumulator



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ISUZU KB P190 2007

5A-10 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 accumulator. As this fluid
returns into the system, the spring forces the piston back to its original position.
The inlet valve opens and fluid may return to the master
cylinder. Conventional braking is then resumed.

RTW 75AMF000501
Legend
(1) Master Cylinder (5) Brake
(2) Brake Pedal (6) Outlet Valve
(3) Motor and Pump (7)Inlet Valve
(4) Accumulator



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ISUZU KB P190 2007

5A-22 BRAKE CONTROL SYSTEM
System Components
Electronic Hydraulic Control Unit (EHCU), four W heel
Speed Sensors, two W arning Lamps, and G sensor.

Electronic Hydraulic Control Unit (EHCU)
The EHCU consists of ABS control circuits, fault
detector, and a fail-safe. It drives the EHCU 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
left side. It consists of a motor, solenoid valves and a
fail safe relay.
Solenoid Valves: Reduces or holds the caliper fluid
pressure for each front brake or both rear brakes
according to the signal sent from the EHCU.
Buffer chamber: Temporarily holds the brake fluid that
returns from the front and rear brake so that pressure of
front brake can be reduced smoothly.
Motor: Drives the pump according to the signal from
EHCU.
Fail safe Relay: W hen failure occurs in ABS.
The power supply to solenoid Valve is cut.

ABS Warning Lamp


RTW 75ASH000101
Vehicles equipped with the Anti-lock Brake System
have an amber “ABS” warning lamp on the instrument
panel. The “ABS” warning lamp will illuminate if a
malfunction in the Anti-lock Brake System is detected
by the Electronic Hydraulic Control Unit (EHCU). In the
case of an electronic malfunction, the EHCU will turn
“ON” the “ABS” warning lamp and disable the anti-lock
braking function.

The “ABS” warning lamp will turn “ON” for
approximately three seconds after the ignition switch is
in the “ON” position.
If the “ABS” warning lamp stays “ON” after the ignition
switch is in 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
diagnostic procedure.

Wheel Speed Sensor (WSS)
It consists of a sensor and a rotor. The sensor is
attached to the knuckle on the front wheels and to the
rear wheels.
The rotor is press-fit in the axle shaft.

G Sensor
The G sensor detects the vehicle deceleration speed
and sends a signal to the EHCU. In 4W D 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
the road surface is low or high, and changes the
EHCU's operating system to ensure ABS and EBD
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 feature is being used.
W hen 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.




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ISUZU KB P190 2007

BRAKE CONTROL SYSTEM 5A-23
Electronic Brake-force Distribution (EBD) System
ABS has the EBD function. EBD is a function which
controls braking force distribution of a front wheel and a
rear wheel, and makes brake fluid pressure of a rear
wheel the optimal. If the rate of slip of a rear wheel
becomes greater compared to a front wheel, the brake
fluid pressure of a rear wheel will be controlled in order
to perform braking force distribution between the front
and rear wheels. EBD enables the braking power of a
rear wheel to always be utilized for the maximum
according to the load change concerning the back axis
according to the vehicle’s loading state (No luggage,
loading, etc.), deceleration, etc. Brake fluid pressure
control to a rear wheel is performed by the EBD function
which uses the ABS function without the mechanical
proportioning valve.
C05L300016
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
CKT
Circuit
DLC
Data Link Connector
EBD
Electronic Brake-force Distribution
EHCU
Electronic Hydraulic Control Unit
FL
Front Left
FR
Front Right
GEN
Generator
H/U
Hydraulic Unit
MV
Millivolts
RR
Rear
RPS
Revolutions per Second
VDC
DC Volts
VAC
AC Volts
W/L
W arning Lamp
WSS
W heel Speed Sensor

General Diagnosis
General Information
ABS problems can be classified into two types, those
which can be detected by the ABS warning lamp 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 FLOW CHART” 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 W rench
• Brake Fluid
• Special Tool
Some diagnosis procedures in this section require the
installation of a special tool.

5-8840-0366-0 High Impedance Multimeter
W hen circuit measurements are requested, use a circuit
tester with high impedance.

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ISUZU KB P190 2007

5A-40 BRAKE CONTROL SYSTEM
Basic Inspection Procedure
1. Basic Inspection of Service Brake
Step Action
Value(s) Yes No
1 Is the fluid level normal?
- Go to Step 2 Replenish with
fluid
Go to Step 2
2 Does fluid leak? - Repair
Go to Step 3 Go to Step 3
3 Is the booster function normal? - Go to Step 4 Repair
Go to Step 4
4 Is the pad and rotor normal? - Go to Step 5 Repair
Go to Step 5
5 Reconnect all components. Ensure all components are properly mounted.
Is this step finished? - Finished Go to Step 5

2. Ground Inspection
Step Action
Value(s) Yes No
1 Are ABS related ground points normal?
- Go to Step 2 Repair
Go to Step 2
2 Reconnect all components. Ensure all component are properly mounted.
Is this step finished? - Finished Go to Step 2



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ISUZU KB P190 2007

5C-20 BRAKES

•
••
•
Operation
The operation of the P-valve by the master cylinde
r
pressure is unchanged up to the brake points
A and B.
If master cylinder fluid pressure penetrates into the second break point
B, the fluid pressure pressing against the seal
, (which isolated route 4 and route 5), passing the route
4of the master cylinder side, overcomes the operating
force of the spring
3 + fluid pressure affecting the seal 2of
the wheel cylinder, and presses the piston
1to the right
side, resulting in the opening of the routes
4 and 5, and
canceling of the P-valve operation.
Then, because the master cylinder fluid pressure and the wheel cylinder fluid pressure, up to the point
C, operate on
the identical surface of the seal
, both have identical
ascending ratios.
However, because of the operation of spring
3in the wheel
cylinder side, wheel cylinder fluid pressure operates to
preserve the balance against the master cylinder fluid
pressure on the lower level with the difference in pressure
resulting from this spring.




RTW 75CSH001601

Valve Maintenance
In the case of a fluid leak or other abnormality, the faulty valve
should be replaced.
The valve is set up at the engine room.
Note:
The blend proportioning valve is not repairable and must
be replaced as a complete assembly.





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ISUZU KB P190 2007