oil ISUZU TROOPER 1995 Workshop Manual

8-382 CHASSIS ELECTRICAL
SUPPLEMENTAL RESTRAINT SYSTEM (SRS)-AIR BAG
The system consists of the starter switch, Diagnostic Energy Reserve Module (OERM), dual pole arming
sensor,
SRS coil assembly, inflator module (driver & passenger), forward sensor and warning light.
SRS is mainly comprised of the deployment loop and the DERM.
The main function of the deployment loop is to flow current into the inflator modules inside the steering
wheel (driver side) and the passenger side instrument panel (passenger side) to inflate the air bag. The
forward sensor
(LH and /or RH) gets activated by a shock caused by collision during running of a vehicle, the
current
from the battery flows into the inflator modules through dual pole arming sensor, so that the air bag
is
inflated.
The DERM supplies the current to the deployment loop to ensure that the air bag is inflated, if the power
circuit between battery and deployment loop is cut off by the shock of collision.
In
addition, the DERM monitors a voltage drops between components, and if the voltage drops below the
specified
value, the driver is alerted by the "AIR BAG" warning light in meter assembly.
Refer to Section 9J "SUPPLEMENTAL RESTRAINT SYSTEM (SRS)-AIR BAG" for details.
OPERATION OF THE CIRCUIT
DRIVER
INFLATOR MODULE
FOWARD
SENSOR-LH
D
D
STARTER SW
D
1
DUAL POLE ARMING SENSOR
PASSENGER
INFLATOR
MODULE
FORWARD
SENSOR-RH
NOTE: Arrow marks "c::::>" indicate the direction of current
Fig. 8-438
•

(
PASSENGER
INFLATOR
MODULE
H-14
RELAY
& FUSE
BOX
H-50
(Fl-l,FL-21
"T1 ce·
BATTERY
00 I .J>. ~
C-49
FORWARD
SENSOR
(RHI
FORWARD
SENSOR
(LHI
(
(
SRS
COIL
ASSEMBLY
DRIVER
INFLATOR
MODULE
FUSE
BOX
(C-1,C-21,C-22,C-23,C-241
C-48
CONDENSOR
!NCI
;g ~ r-0 0 ~ -0 2
0 ::t ):lo en
en c;; m r­m 0 -t :a ~ r-eo I w co w

9J-4 Supplemental Restraint System
'"""'t::~h-l--"b~RM PASSENGER SlOE HIGH
SYSTEM DESCRIPTION
The main portions of the SRS are the deployment loops ~
and the Diagnostic Energy Reserve Module(DERM).
The main function of the deployment loops is to supply
current through the inflator modules,which will cause
deployment of the air bags in the event of a frontal crash
of sufficient force, up to
30 degrees off the centerline of
the vehicle.The dual pole arming sensor, SRS coil
assembly(
driver side only), inflator modules, LH forward
discriminating sensor and
RH forward discriminating
sensor make up the
deployment loops. The dual pole
arming sensor switches power to the inflator modules on
the high side(power side) of the
deployment loops. Either
of the discriminating sensors can
supply ground to the
inflator modules on the low side (ground side) of the
loops. The inflator modules are only supplied sufficient
current to
deploy when the dual pole arming sensor and
at
least one of the discriminating sensors are closed
simultaneously.
A function of the DERM is to supply the deployment loops
with a 36-Volt Loop Reserve(36VLR) to ensure sufficient
energy to
deploy the air bags if the ignition feed to the
dual pole arming sensor is lost during a frontal crash.
Another function of the DERM is electrical system
diagnostics. The DERM monitors the deployment loops
in conjunction with the resistors in the dual pole arming
sensor, LH
forward discriminating sensor and RH
forward discriminating sensor. These resistors make it
possible for the DERM to detect circuit and component
malfunctions within the deployment loops. The DERM
monitors the
voltage drop across each component within
the
loops during normal non-deployment operation. If
the monitored voltages fall outside of expected limits, the
DERM
will indicate a malfunction through the storage of
a diagnostic trouble code and the illumination of the "AIR
BAG"
warning lamp.

(
PASSENGER
INFLATOR
MODULE
RELAY
& FUSE
BOX
(FL-l,FL-2) BATTERY
FORWARD
SENSOR
IRH)
(
(
SRS
COIL
ASSEMBLY
DRIVER
INFLATOR
MODULE
FUSE
BOX
(C-1,C-21,C-22,C-23,C-24)
CONDENSOR
(A/C)
t/) :::0 t/) 0 0 s:: "tJ 0 z m z -1 )> z c == -:::0 -z C) r-0 0 ~ -0 z
< -m ==
en c "tJ
"tJ a; 3 CD :::J -!. lJ CD (I) -!. :::J -en i 3 U) c.. I c.n

SRS COIL ASSEMBLY
The SRS coil assembly consists of two current carrying
coils. They are attached to the steering column and allow
rotation of the steering wheel while maintaining
continuous contact of the driver deployment loop to the
driver inflator module.
There is a shorting clip on the yellow
3-way connector
near the base of the steering column which connects the
SRS coil to the SRS wiring harness. The shorting clip
shorts the circuits to the
SRS coil and driver inflator
module when the yellow 3-way connector is
disconnected. The circuit to the driver inflator module is
shorted
in this way to help prevent unwanted deployment
of the air bag when servicing the steering column or other
SRS components.
INFLATOR MODULES
The inflator modules consist of an inflatable bag and an
inflator(a canister of gas-generating material and an
initiating device). When the vehicle is in a frontal crash
of sufficient force to close the dual pole arming sensor
and at least one of the discriminating sensors
simultaneously, current flows through the deployment
loops. Current passing through the initiator ignites the
material
in the inflator module. The gas produced from
this reaction rapidly inflates the air bag.
There is a shorting clip
on the driver inflator module side
of the upper steering column connector which connects
the
SRS coil assembly to the driver inflator module. The
shorting clip shorts across the driver inflator module
circuits when the upper steering column connector is
disconnected. The circuit to the driver inflator module is
shorted
in this way to help prevent unwanted deployment
of the air bag when servicing the driver inflator module,
the steering column
or other SRS components.
There is a shorting clip on the passenger inflator module
connector which connects to the passenger inflator
module jumper. The shorting clip shorts across the
passenger inflator module circuit when the passenger
inflator module connector is disconnected. The circuit to
the passenger inflator module is shorted in this way to
help prevent unwanted deployment of the air bag when
servicing the passenger inflator module, the instrument
panel or other
SRS components.
STEERING COLUMN
The steering column absorbs energy and is designed to
compress in a frontal crash to decrease the chance of
injury to the driver. A steering column reinforcement is
also used for additional support.
KNEE BOLSTER
The knee bolsters are used to absorb energy and control
the forward movement of the vehicle's front seat
occupants during a frontal crash, by limiting leg
movement.
Supplemental Restraint System 9J-7

9J-8 Supplemental Restraint System
DEFINITIONS
AIR BAG -An inflatable cloth cushion designed to
deploy in certain frontal crashes. It supplements the
protection offered by the seat belts by distributing the
impact load more evenly over the vehicle occupant's
head and torso.
ASYNCHRONOUS -Performed in a non-periodic
fashion,i.e.no defined time or interval.
B+-Battery voltage, the voltage available at the battery
at the time of the indicated measurement. With the key
"ON" and the engine not running, the system voltage will
likely be between 12 and 12.5 volts. At idle the voltage
may be 14 to 16 volts. The voltage could be as low as 1
0
volts during engine cranking.
BULB
CHECK-The DERM will cause the "AIR BAG"
warning lamp to flash seven times and then go "OFF"
whenever the ignition switch transitions to the RUN
position from any other ignition switch position and no
malfunctions are detected.
"CONTINUOUS MONITORING"-Tests performed by
the DERM on the
SRS every 1 00 milliseconds while
"Ignition
1" voltage is in the normal operating voltage
range at the DERM.
DATA LINK CONNECTOR(DLC)-Formerly "ALDL'', a
connector which allows communication with an
off-board 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 inflator modules to deploy the air bag.
DERM -Diagnostic
energy reserve module which
provides reserve energy to the deployment loops and
performs diagnostic monitoring of
all SRS components.
DIAGNOSTIC TROUBLE CODE(DTC) -Formerly
"Code,"a numerical designator used by the DERM to
indicate specific
SRS malfunctions.
DRIVER CURRENT SOURCE-An output of the DERM
which injects current into the driver inflator module circuit
during the "Initiator Assembly Resistance
Test."
DRIVER INFLATOR
MODULE-An assembly located in
the steering wheel hub consisting of an inflatable air bag,
an inflator and an initiator.
DUAL
POLE ARMING SENSOR-A sensor on the high
side(power side) of the deployment loops that is
calibrated to supply voltage to the inflator modules when
the vehicle velocity changes are severe enough to
warrant arming of the air bags in preparation for
deployment.
EEPROM -Electrically Erasable Programmable Read ~
Only Memory. Memory which retains its contents when
power
is removed from the DERM.
FORWARD LH DISCRIMINATING SENSOR-A sensor
on the low side(ground side) of the deployment loops
which is calibrated to ground the inflator modules when
the vehicle velocity changes are severe enough to
warrant deployment of the air bags.
FORWARD RH DISCRIMINATING SENSOR-A sensor
on the low side(ground side) of the deployment loops
which
is calibrated to ground the inflator modules when
the vehicle velocity changes are severe enough
to
warrant deployment of the air bag.
FORWARD LH SENSOR Eng-Room HARNESS-An
assembly of two correct carrying wires which connects
the Forward
LH discriminating sensor to SRS harness.
FORWARD RH SENSOR Eng-Room HARNESS
JUMPER-An assembly of two current carrying wires
which connects the Forward
RH discriminating sensor to
the
SRS harness.
HIGHER PRIORITY FAULT-Each diagnostic trouble
code
is assigned a priority based on the detectability with
other DTCs present. The priority corresponds to the
detectability of the malfunction ONLY, and does NOT
relate to the criticality of the malfunction with respect to ~
deployment or non-deployment under any given
condition.
IGNITION CYCLE -The voltage at the PERM "Ignition
1"
inputs, with ignition switch "ON," is within the normal
operating voltage range for at least ten seconds before
turning ignition switch
"OFF."
IGNITION1
-A battery voltage(B+)circuit which is only
powered with the ignition switch in the RUN,BULB
TEST,or START positions.
INITIATOR-The electrical component inside the inflator
module which, when sufficient current flows, sets off the
chemical reaction that inflates the air bag.
"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
DERM configuration for the vehicle, shorts to
"Ignition 1"
in the deployment loops, high resistance or opens in the
"Driver
Side High," "Driver Side Low," "Passenger Side
High"
and "Passenger Side Low" 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 DERM "Ignition 1" ·
terminals and "Ground" terminals is between 7.25 and 16
volts.
•

PASSENGER CURRENT SOURCE -An output of the
DERM which injects current into the passenger inflator
module circuit during the
~Initiator Assembly Resistance
'--"" Test."
PASSENGER INFLATOR MODULE -An assembly
located in the right side of the 1/P consisting of an
inflatable bag, an inflator and an initiator.
SCAN TOOL -An off-board computer used to read
diagnostic information from on-board computers via the
data
link connector.
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 inflator module.
SRS WIRING HARNESS-The wires and connectors
that electrically connect the components in the
SRS.
1 Supplemental Restraint System 9J-9
"10 MINUTE LOOP TEST' -Portions of the "Initiator
Assembly Resistance Test" are repeated every ten
minutes during an ignition cycle. These are the check for
shorts to
"Ignition 1" in the deployment loops and the
check for an open discriminating sensor interconnect
circuit.
''TURN-ON" -Test which the DERM performs on the
SRS once during each ignition cycle immediately after
"Ignition 1" voltage is applied to the DERM and before
"Continuous Monitoring."
36VLR-The 36-volt loop reserve energy supplies from
the DERM which provide deployment power when
vehicle voltage is
low or lost in a frontal crash.
36 VLR DELAY
-Changing of the 36 VLR power supplies
is
inhibited briefly during "Turn-ON." This allows
detection of certain malfunctions related to "Ignition 1"
voltage which cannot be tested with 36 volts present.

9J-12 Supplemental Restraint System

REPAIRS AND INSPECTIONS REQUIRED AFTER AN
ACCIDENT
NOTE
• If
any SRS components are damaged, they must be
replaced. If SRS component mounting points are
damaged, they must be
replaced.
•
Never use SRS parts from another vehicle. This
does not
include remanufactured parts purchased
from an authorized
dealer; they may be used for SRS
repairs.
• Do not attempt to service discriminating sensors, the
dual pole arming sensor, the DERM, the SRS coil
assembly,
or the inflator modules. Service of these
items is by
replacement only.
•
Verify the part number of replacement inflator
modules.
CAUTION: PROPER OPERATION OF THE
SENSORS AND SUPPLEMENTAL RESTRAINT
SYSTEM (SRS) REQUIRES THAT ANY REPAIRS TO
THE VEHICLE STRUCTURE RETURN IT TO THE
ORIGINAL PRODUCTION CONFIGURATION.
DEPLOYMENT REQUIRES, AT A MINIMUM,
REPLACEMENT OF THE SENSORS, THE INFLATOR
MODULE,
AND DIMENSIONAL INSPECTION OF THE
STEERING COLUMN. ANY VISIBLE DAMAGE TO
THE DERM MOUNTING BRACKET(S) REQUIRES
REPLACEMENT, SENSORS MUST BE REPLACED,
AND THE
STEERING COLUMN MUST BE
DIMENSIONALLY INSPECTED, WHETHER
DEPLOYMENT
OCCURRED OR NOT.
ACCIDENT WITH DEPLOYMENT-COMPONENT
REPLACEMENT AND
INSPECTIONS
Certain SRS components must be replaced for damage
after a
frontal crash involving air bag deployment. Those
components are:
• Inflator modules.
• All
sensors. It is include among the Dual pole Arming
Sensor.
CAUTION
•
Refer to "Sensor Replacement Guidelines"
below for Important Information on sensor
replacement In both deployment and
non-deployment crashes.
• SRS coil assembly, Inspect wiring and connector for
any signs of scorching,
melting, or damage due to
excessive heat.
Replace if damaged. Refer to this in
section
3.
ACCIDENT WITH OR WITHOUT DEPLOYMENT­
COMPONENT INSPECTIONS
Certain SRS and restraint system components must be
inspected after any crash, whether the air bag
deployed
or not. Those components are:
• Steering column-Dimensionally inspect per
"Checking Steering Column for Accident Damage" in
section 3.
• Sensors, if in the area of accident damage. If with
deployment, All sensors must be replaced.
CAUTION
•
Refer to "Sensor Replacement Guidelines"
below for Important information on sensor
replacement in both deployment and
non-deployment crashes.
• Knee bolsters and mounting points-Inspect for any
distortion, bending, cracking, or other damage.
• 1/P steering column reinforcement plate-Inspect for
any distortion, bending, cracking, or other damage.
• liP braces-Inspect for any distortion, bending,
cracking, or other damage.
~
• Seat belts and mounting points-Refer to "Seat Belts"
in SECTION 10.
SENSOR REPLACEMENT GUIDELINES
SRS sensor replacement policy requires replacement of
the all sensors, after crash Involving Air Bag
Deployment.
WIRING DAMAGE
If any SRS wire harness is damaged, it should be
replaced. Don't repair SRS HARNESS. It is replace only.
SRS CONNECTOR {PLASTIC BODY AND
TERMINAL METAL PIN) DAMAGE
If any connector or terminal in the SRS wire harness
(except
pigtails) is damaged, it should be replaced.
SRS WIRE PIGTAIL DAMAGE
If the wiring pigtail (a wire or wires attached directly to the
device,
not by a connector)is damaged, the entire
component(with pigtail)must be replaced. Examples of
"pigtail" components are the driver inflator module, the
passenger
inflator module, the discriminating sensors,
the
dual pole arming sensor and the SRS coil assembly. ~
SRS WIRE DAMAGE
If any wire except the pigtail is damaged, the wire should
be replaced.
Ill

, Supplem~l Restraint System
SPECIAL TOOLS
WARNING: TO AVOID DEPLOYMENT WHEN
'-' TROUBLESHOOTING THE SRS, DO NOT USE
ELECTRICAL TEST EQUIPMENT SUCH AS A
BATTERY-POWERED OR AC-POWERED
VOLTMETER, OHMMETER, ETC., OR ANY TYPE OF
ELECTRICAL EQUIPMENT OTHER THAN THAT
SPECIFIED IN THIS MANUAL. DO NOT USE A
NON-POWERED PROBE TYPE TESTER.
INSTRUCTIONS IN THIS MANUAL MUST BE
FOLLOWED CAREFULLY, OTHERWISE PERSONAL
INJURY
MAY RESULT.
SRS DRIVER/PASSENGER LOAD TOOL
The SRS Driver/Passenger Load Tool J-41433 is used
only when called for in this section. It is used as a
diagnostic aid and safety device to prevent inadvertent
inflator
module deployment.
The
load tool has four yellow connectors attached to its
case.
The three
small connectors are electrically functional
and serve as resistive
load substitutions. The large
dummy connector does not serve as a load substitution
but
merely takes the physical place of the DERM
connector when needed.
No more than two connectors are used at any time.
One
of the small connectors is used to substitute for the load
of the driver inflator module when it is connected at the
top of the
column to the SRS coil assembly. Another
small connector is used to substitute for the load of the
driver inflator
module and the SRS coil assembly when
it is connected at the base of the
column to the SRS
wiring harness. The third small connector is used to
substitute for the
load of the passenger inflator module
when connected to the passenger inflator module
harness connector.
By substituting the resistance of the
load tool when called
for, a determination can be made as to whether an
inflator circuit component is causing system malfunction
and which component is causing the malfunction. The
load tool should be used only when specifically called for
in the diagnostic procedures.
9J-25

9J-54 Supplemental Restraint System
DTC21
DRIVER INITIATOR CIRCUIT RESISTANCE HIGH
CIRCUIT DESCRIPTION
During the "Initiator Assembly resistance Test" the
DERM grounds the
"Passenger Side Low" terminal "B7"
and turns "ON" the driver current source at

the
"Driver
Side
High" terminal "B9". This causes a known amount
of Current to flow through the driver initiator circuit. By
monitoring the difference between the voltage at the
"Driver Side High" terminal "B9" and the "Driver Side
Low'' terminal "B8" the DERM calculates the combined
resistance of the driver inflator module, SRS coil
assembly, harness wiring CKTs IB16, IB17 and IB19 and
connector terminal contact.
DTC WILL SET WHEN
The combined resistance of the driver inflator module,
SRScoilassembly, harness wiring
CKT's IB16, IB17 and
IB19 and connector terminal contact is above a specified
value. This test is run during the
"Initiator Assembly
Resistance
Test" when: 1) No "higher priority faults" are
detected during
"Turn-QN," 2) No "higher priority faults"
are detected during
"Continuous Monitoring" for one
second, 3) No
"Crank" signal present, 4) "Ignition 1"
voltage is above a specified value.
ACTION TAKEN
DERM turns "ON" the "AIR BAG" warning lamp and sets
diagnostic trouble code.
FUSE
TO IGNITION SRS C-2310A 11105 SWITCH
TO
IGNITlON SWITCH
~i SRS
C-24 lOA 1800 AD
DTC WILL CLEAR WHEN
The ignition switch is turned "OFF."
DTC CHART TEST DESCRIPTION
Number(s) below refer to step number(s) on the
diagnostic chart.
2. This test determines whether the malfunction is in
the driver inflator module circuitry or
in the DERM
wiring harness circuitry.
3. This test determines whether the malfunction is an
open in IB19.
DIAGNOSTIC AIDS
An intermittent condition is likely to be caused by a poor
connection at: the yellow
2-way connector near the base
of the steering column, DERM terminals
"B8" or "B9", or
the connection at the top of steering column to the driver
inflator module.
SRS·l JOINT CONNECTION
" FUSE SRS C-2210A
BL ED
1800
1807 1111 1812 1113 11114
IGNITION! IGNITION 1
DRIVER 36VLR PASS. 36VLR PASS. SOURCE
SENSE
REDUNDAT INDICATOR GROUND
SRS·1 PASS SIDE HIGH
PASS SIDE LOW
IB34
1831 FUSE STARTER C-10A
SERIAL DATA FUSE
11120
1803
SRS INDICA TOR
•