2004 ISUZU TF SERIES instrument panel

9A-4 SUPPLEMENTAL RESTRAINT SYSTEM

Service Precaution
WARNING: THIS VEHICLE HAS A SUPPLEMENTAL
RESTRAINT SYSTEM (SRS). REFER TO THE SRS
COMPONENT AND WIRING LOCATION VIEW IN
ORDER TO DETERMINE WHETHER YOU ARE
PERFORMING SERVICE ON OR NEAR THE SRS
COMPONENTS OR THE SRS WIRING. WHEN YOU
ARE PERFORMING SERVICE ON OR NEAR THE
SRS COMPONENTS OR THE SRS WIRING, REFE
R
TO THE SRS SERVICE INFORMATION. FAILURE
TO FOLLOW WARNINGS COULD RESULT IN
POSSIBLE AIR BAG DEPLOYMENT, PERSONAL
INJURY, OR OTHERWISE UNNEEDED SRS
SYSTEM REPAIRS.
CAUTION: Always use the correct fastener in the
proper location. When you replace a fastener, use
ONLY the exact part number for that application.
ISUZU will call out those fasteners that require a
replacement after removal. ISUZU will also call out
the fasteners that require thread lockers or thread
sealant. UNLESS OTHERWISE SPECIFIED, do not
use supplemental coatings (Paints, greases, o
r
other corrosion inhibitors) on threaded fasteners
or fastener joint interfaces. Generally, such
coatings adversely affect the fastener torque and
the joint clamping force, and may damage the
fastener. When you install fasteners, use the
correct tightening sequence and specifications.
Following these instructions can help you avoid
damage to parts and systems.
General Description
CAUTION: When fasteners are removed, always
reinstall them at the same location from which
they were removed. If a fastener needs to be
replaced, use the correct part number fastener fo
r
that application. If the correct part numbe
r
fastener is not available, a fastener of equal size
and strength (or stronger) may be used.
Fasteners that are not reused, and those requiring
thread locking compound will be called out. The
correct torque value must be used when installing
fasteners that require it. If the above conditions
are not followed, parts or system damage could
result.


Restraint Devices
827RW006
Legent
(1) Deployed Air Bag
(2) Knee Bolster
(3) Seat Belt


The Supplemental Restraint System (SRS) helps
supplement the protection offered by the driver and
front passenger seat belts by deploying an air bag
from the center of the steering wheel and from the
front of the passenger side of the instrument panel.
The air bag deploys when the vehicle is involved in a
frontal crash of sufficient force up to 30 degrees off the
centerline of the vehicle. To further absorb the crash
energy there is a knee bolster located beneath the
instrument panel for both the driver and passenger,
and the steering column is collapsible.

827RW005

SUPPLEMENTAL RESTRAINT SYSTEM 9A-9

060R300007

SRS Coil Assembly
The SRS coil assembly consists of two current
carrying coils. This is attached to the steering column
and allow rotation of the steering wheel while
maintaining continuous contact of the driver
deployment loop to the driver air bag assembly.
There is a shorting clip on the yellow connector near
the base of steering column which connects the SRS
coil to the SRS wiring harness.
The shorting clip shorts to the SRS coil and driver air
bag assembly when the yellow connector is
disconnected. The circuit to the driver air bag
assembly is shorted in this way to help prevent
unwanted deployment of the air bag when servicing
the steering column or other SRS components.
060R300047


Air Bag Assemblies
The air bag assembly consist of an inflatable air bag
assembly and an inflator. When the vehicle is in a
frontal crash of sufficient force.
The SRS control unit causes current flow through the
deployment loops. Current passing through the inflator
ignites the material in the air bag assembly. The gas
produced from this reaction rapidly inflates the air bag
assembly.
There is a shorting clip on the driver air bag assembly
connector which connects the SRS coil assembly. The
shorting clip shorts across the driver air bag assembly
circuits when driver air bag assembly connector is
disconnected.
The circuit to the driver air bag assembly is shorted in
this way to help prevent unwanted deployment of the
air bag when servicing the driver air bag assembly, the
steering column or other SRS components.

060R300012

There is a shorting clip on the passenger air bag
assembly connector which connects to the SRS
harness. The shorting clip shorts across the
passenger air bag assembly circuit when the
passenger air bag assembly connector is
disconnected. The circuit to the passenger air bag
assembly is shorted in this way to help prevent
unwanted deployment of the air bag when servicing
the passenger air bag assembly, the instrument panel
or other SRS components.

SUPPLEMENTAL RESTRAINT SYSTEM 9A-11

“Continuous Monitoring”
Tests performed by the SRS control unit on the SRS
every 100 milliseconds while “Ignition 1” voltage is in
the normal operating voltage range at the SRS control
unit.
Data Link Connector (DLC)
Formerly “DLC” a connector which allows
communication with an external computer, such as a
scan tool.
Datum Line
A base line parallel to the plane of the underbody or
frame from which all vertical measurements originate.
Deploy
To inflate the air bag.
Deployment Loops
The circuits which supply current to the air bag
assemblies to deploy the air bag.
Diagnostic Trouble Code (DTC)
Formerly “Code”, a numerical designator used by the
SRS control unit to indicate specific SRS malfunctions.
Driver Current Source
An output of the SRS control unit which applies current
into the driver air bag assembly circuit during the
“Initiator Assembly Resistance Test”.
“Initiator Assembly Resistance Test”
Tests performed once each ignition cycle when no
malfunctions are detected during “Turn–ON” or
“Continuous Monitoring”. This test checks for the
correct SRS control unit configuration for the vehicle,
shorts to “Ignition 1” in the deployment loops, high
resistance or opens in the “Driver Side” and
“Passenger Side” circuits and measures the resistance
of the inflator assembly consisting of 1) Initiators, 2)
SRS coil assembly (driver side only), 3) Connectors
and associated wiring.
Normal Operating Voltage Range
The voltage measured between the SRS control unit
“Ignition 1” terminals and “Ground” terminals is
between 9 and 16 volts.
Passenger Current Source
An output of the SRS control unit which applies current
into the passenger air bag assembly circuit during the
“Initiator Assembly Resistance Test”.
Passenger Air Bag Assembly
An assembly located in the front of the passenger side
of the instrument panel consisting of an inflatable bag,
an inflator and an initiator.
Scan Tool
An external computer used to read diagnostic
information from on–board computers via the data link
connector.
SRS control unit
SRS control unit which provides reserve energy to the
deployment loops, deploys the air bags when required
and performs diagnostic monitoring of all SRS
components.
Serial Data
Information representing the status of the SRS.
SRS
Supplemental Restraint System.
SRS Coil Assembly
An assembly of two current–carrying coils in the driver
deployment loop that allows the rotation of the steering
wheel while maintaining the continuous contact of the
driver deployment loop to the driver air bag assembly.
SRS Wiring Harness
The wires and connectors that electrically connect the
components in the SRS.
“Turn–ON”
Test which the SRS control unit performs on the SRS
once during each ignition cycle immediately after
“Ignition 1” voltage is applied to the SRS control unit
and before “Continuous Monitoring”.

SUPPLEMENTAL RESTRAINT SYSTEM 9A-15

On–Vehicle Service
Service Precaution
WARNING: WHEN PERFORMING SERVICE ON OR
AROUND SRS COMPONENTS OR SRS WIRING,
FOLLOW THE PROCEDURES LISTED BELOW TO
TEMPORARILY DISABLE THE SRS. FAILURE TO
FOLLOW PROCEDURES COULD RESULT IN
POSSIBLE AIR BAG DEPLOYMENT, PERSONAL
INJURY OR OTHERWISE UNNEEDED SRS
REPAIRS.
The SRS control unit in Driver–Passenger SRS can
maintain sufficient voltage to cause a deployment for
up to 15 seconds after the ignition switch is turned
“OFF,” the battery is disconnected, or the fuse
powering the SRS control unit is removed.
Many of the service procedures require removal of the
“SRS” fuse, and disconnection of the air bag assembly
from the deployment loop to avoid an accidental
deployment. If the air bag assembly is disconnected
from the deployment loop as noted in the “Disabling
the SRS” procedure that follows, service can begin
immediately without waiting for the 15 second time
period to expire.

Disabling The SRS
Removal
Turn the ignition switch to “LOCK” and remove key.
1. Remove SRS fuse “SRS”, from the side of the
driver side of instrument panel fuse block o
r
disconnect battery.
2. Disconnect yellow connector at the base o
f
steering column.
3. Remove glove box assembly, refer to “Passenge
r
Air Bag Assembly Replacement” in this manual.
4. Disconnect yellow connector behind the glove box
assembly.
CAUTION: With the “SRS” fuse removed and
ignition switch “ON”, the “AIR BAG” warning lamp
will be “ON”. This is normal operation and does
not indicate an SRS malfunction.

Enabling The SRS
Installation
CAUTION: Never use the air bag assembly from
another vehicle and difference model year air bag
assembly.
Use only new air bag assembly proper to the
TFR/S which is being repaired.
Turn ignition switch to “LOCK” and remove key.
1. Connect yellow connector passenger air bag
assembly.
2. Install glove box assembly. Refer to “Passenger ai
r
bag assembly replacement” in this manual.
3. Connect yellow connector at the base of steering
column.
4. Install “AIR BAG” fuse “SRS” to the side of the
driver side of instrument panel fuse block o
r
connect battery.
Turn ignition switch to “ON” and verify that the “AIR
BAG” warning lamp flashes seven times and then
turns “OFF.” If it does not operate as described,
perform the “SRS Diagnostic System Check” in this
manual.

Handling / Installation / Diagnosis
1. Air bag assembly should not be subjected to
temperatures above 65

C (150
F).
2.
Air bag assembly, and SRS control unit should not
be used if they have been dropped from a height
of 100 centimeters (3.28 feet) or more.
3. When a SRS control unit is replaced, it must be
oriented with the arrow on the sensor pointing
toward the front of the vehicle. It is very important
for the SRS control unit to be located flat on the
mounting surface, parallel to the vehicle datum
line. It is important that the SRS control unit
mounting surface is free of any dirt or other foreign
material.
4. Do not apply power to the SRS unless all
components are connected or a diagnostic chart
requests it, as this will set a diagnostic trouble
code.
5. The “SRS Diagnostic System Check” must be the
starting point of any SRS diagnostics. The “SRS
Diagnostic System Check” will verify proper “AIR
BAG” warning lamp operation and will lead you to
the correct chart to diagnose any SRS
malfunctions. Bypassing these procedures ma
y
result in extended diagnostic time, incorrect
diagnosis, and incorrect parts replacement.

9A-28 SUPPLEMENTAL RESTRAINT SYSTEM

– Driver air bag assembly
– Passenger air bag assembly
– Steering wheel
– SRS coil assembly
– Steering column
– Knee bolster and instrument panel mounting
attachments
– Driver seat and belt
– Passenger seat and belt
– SRS control unit
SRS control unit always should be checked according
to “SRS Control Unit Replacement Guidelines.”
CAUTION: Refer to “SRS control unit Replacement
Guidelines” below for important information on
SRS control unit replacement in both deployment
and non–deployment crashes.
Inspect SRS coil assembly wiring and steering wheel
for any sign of scorching, melting, or damage due to
excessive heat. If coil assembly wire or steering wheel
is damaged, replace them. The steering column and
wheel must be dimensionally checked to determine if
they are damaged. Refer to steering wheel of in this
manual.
Never use SRS parts from another vehicle. This does
not include remanufactured parts purchased from an
authorized Isuzu Retailer; they may be used for SRS
repairs.
Do not attempt to repair the SRS control unit, the SRS
harness, the SRS coil assembly, the air bag assembly,
the steering wheel, or the steering column. Service of
these items is replacement only. Verify replacement
part numbers.
CAUTION: Proper operation of the SRS control
unit and supplemental restraint system (SRS)
requires that any repairs to the vehicle structure
return it to its original production configuration.

SRS Connectors
CAUTION: The special yellow color connectors are
used for supplemental restraint system-air bag
circuit. When removing the cable harness, do not
pull the cables otherwise, cable disconnection
may occur. When connect the SRS connector,
insert the connector completely. Imperfect locking
may cause malfunction of SRS circuit.


Removal
To remove the connector, hold the cover insulator (1)
and pull it. The cover insulator slides and lock will be
released. Do not hold the socket insulator (2).
827RW028

9A1-36 RESTRAINT CONTROL SYSTEM

DTC (Flash Code33) B0033 ECU Connector Poor Connection

Step Action Yes No
1 Was the “SRS Diagnostic System Check” performed?
Go to Step 2 Go to the “SRS
Diagnostic System
Check”
2 Ignition switch “OFF”
Reconnect the ECPA on SRS control unit connector yellow 52-
pin connector located at the base of instrument panel center.
Ignition switch “ON”
Is DTC B0033 current? Go to Step 3 Reconnect the
ECPA properly.
Go to Step2
3 Clear Diagnostic trouble codes.
Is the action complete? Go to “SRS
Diagnostic System
Check” Go to Step 3

4C2-2 SHIFT ON THE FLY SYSTEM

Shift On The Fly System
Outline of Shift on The Fly System
The shift on the fly system switches between 2 wheel
drive (2WD) and 4 wheel drive (4WD) electrically b
y
driver's pressing the 4WD switch (push button type) on
instrument panel.
This system controls below operations.
1.
Shifting the transfer front output gear (Connecting to,
and disconnecting from, front propeller shaft b
y
motor actuator).
2. Retrial of shifting the transfer front output gear.
3. Connecting front wheels to, and disconnecting them
from, the front axles by axle motor actuator.
4. Indicator on instrument panel.
5. 4WD out signal to other Electronic Hydraulic Control
Unit.

System Diagrams
RUW34BLF000201

BRAKE CONTROL SYSTEM 5A-19

System Components
Electronic Hydraulic Control Unit (EHCU), four Wheel
Speed Sensors, two Warning 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 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: When failure occurs in ABS.
The power supply to solenoid Valve is cut.

ABS Warning Lamp


825L300001
Vehicles equipped with the Anti-lock Brake System
have an amber “ABS” warning lamp in 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
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
to the “ON” position.
If the “ABS” warning lamp 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 (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 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 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 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.