1998 SSANGYONG MUSSO Workshop Repair Manual

SECTION 8B
SUPPLEMENTAL RESTRAINT SYSTEM(SRS)
Specifications . . . . . . . . . . . . . . . . . . . . . . . . 8B-1
General Specifications . . . . . . . . . . . . . . . . . . 8B-1
Schematic and Routing Diagrams . . . . . . . . 8B-2
Air Bag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8B-2
Cautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8B-3
Function Description . . . . . . . . . . . . . . . . . . 8B-4
Air Bag Module . . . . . . . . . . . . . . . . . . . . . . . . 8B-6
Diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . 8B-7
Description . . . . . . . . . . . . . . . . . . . . . . . . . . . 8B-7
Self Diagnosis . . . . . . . . . . . . . . . . . . . . . . . . 8B-10
Circuit Diagram . . . . . . . . . . . . . . . . . . . . . . . 8B-16
TABLE OF CONTENTS
Caution: Disconnect the negative battery cable before removing or installing any electrical unit or when a
tool or equipment could easily come in contact with exposed electrical terminals. Disconnecting this cable
will help prevent personal injury and damage to the vehicle. The ignition must also be in LOCK unless otherwise
noted.
SPECIFICATIONS
GENERAL SPECIFICATIONS
Application
Air bag System Deployment Time
Detection Time
Operating Temperature
Storage Temperature
Air Bag Replacement Interval
Voltage Range
Current Consumption
Acceleration Range
Max. Acceleration
Voltage Ramp
Energy Reservation
Inflator Ignition Energy
Squib Resistance
Air Bag Warning Lamp ON Time (When Ignition ON)Description
< 20ms
< 5ms
-40°C ~ +85°C
-40°C ~ +90°C
Every 10-year after installation
9-16V
5ms after ignition switch ON < 1A,
5ms ~ 5sec. <300mA, after 5sec. < 100mA
+/-50g
+/-600g pulse
0.5 ~ 2.0 V/s
150ms after battery disconnection
4.3mJ
2.15 ± 0.35 W
6 sec.
Air Bag Diagram . . . . . . . . . . . . . . . . . . . . . . 8B-17
Maintenance and Repair . . . . . . . . . . . . . . 8B-18
On-Vehicle Service . . . . . . . . . . . . . . . . . . . . . 8B-18
Air Bag Module . . . . . . . . . . . . . . . . . . . . . . . 8B-18
Clock Spring . . . . . . . . . . . . . . . . . . . . . . . . . 8B-19
Air Bag Control Unit (AC4) . . . . . . . . . . . . . . 8B-21
General Description and System
Operation . . . . . . . . . . . . . . . . . . . . . . . . 8B-22
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 8B-22
Caution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8B-22

8B-2 SUPPLEMENTAL RESTRAINT SYSTEM(SRS)
SCHEMATIC AND ROUTING DIAGRAMS
AIR BAG

SUPPLEMENTAL RESTRAINT SYSTEM(SRS) 8B-3
CAUTIONS
Failure to follow the correct service procedure can cause air bag damage or personal injury due to unexpected air
bag deployment. Before service (removal and installation of part, check for replacement), please be weal noticed of
following items for your correct service.
1. For service, turn the ignition switch to ‘LOCK’ position and wait for 30 seconds after disconnecting the negative
battery cable.
2. If the vehicle collapsed, remove the air bag ECU first to reserve the crash records.
3, Never use other vehicles’ air bag components and replace with specified new part.
4. Never disassemble or repair the air bag module, air bag unit and wiring harness to re-use.
5. Replace the air bag module and air bag unit with new if it dropped, cracked or damaged.
6. Only qualified technicians in service shop should check or repair the air bag,
7. Before service, should be well noticed of warning labels on the vehicle.
A. Sun Visor Side
[Warning]
Pull down the sun visor and see SRS air bag
warning lamp on the head lining.
B. Head Lining
[Warning]
1 . This vehicle is equipped with air bag. Air bag is
supplemental device for the seatbelt. Fasten
your seatbelt.
2. This air bag should be replaced by authorized
supplier within replacement intervals.
3. When the ignition key is turned to ON position,
SRS warning lamp will turn on for 6 sec. and go
off. In this case, the system is normal.
For the following cases, see service manual.
- SRS warning lamp does not turn on.
- SRS warning lamp does not go off.
- SRS warning lamp continues to blink.
C. Steering Wheel Body Inner
[Warning]
Before removing the steering wheel, read service
manual first. Set the front wheels straight forward
and align the center position marks of SRS clock
spring. Improper removal or installation of the
steering wheel can damage the SRS components.D. Engine Compartment
[Warning]
This vehicle is equipped with air bag. Before
checking the engine compartment, read service
manual first. Faultuy check and service can cause
SRS air bag deployment and system defects that
can be led to severe damage.
E. Battery Cable
[Warning]
Before disconnecting the battery power, read
service manual first.

8B-4 SUPPLEMENTAL RESTRAINT SYSTEM(SRS)
FUNCTION DESCRIPTION
Air Bag Control Unit (AC4)
Air bag control unit (AC4) is installed on the center portion of
the front floor tunnel.
It is a central control unit that control all functions and determines
whether deploy the air bag or not with the collision signal from
the built-in accelerometer sensor and has function of diagnosing
system defects.
Internal air bag control unit is consisted as follows;
lMicroprocessor
lASICs (Upper side ASIC & lower side ASIC)
lAccelerometer sensor
lArming sensor
lSystem energy backup condenser
lSquib energy backup condenser

SUPPLEMENTAL RESTRAINT SYSTEM(SRS) 8B-5
Input & Output Function
Electronic air bag control and diagnosis module is connected
by full 30-pin connectors.
Input : ground
Output : 1 squib line, warning lamp
Input/output : communication, diagnosis
16 Shorting Bar
17 Shorting Bar
18 Shorting Bar
19 Shorting Bar
20 Diagnosis
21 Shorting Bar
22 Shorting Bar
23 No Pin
24 No Pin
25 Shorting Bar
26 Shorting Bar
2 7 N/A
28 Shorting Bar
29 Shorting Bar
3 0 N/A 1 Lamp
2 Ground
3 N/A
4 N/A
5 Ignition
6 N/A
7 N/A
8 CONF
9 N/A
1 0 N/A
11 N/A
1 2 N/A
13 Squib Line 1(upper)
14 Squib Line 1(lower)
1 5 N/A
IGN
GND
Warning lamp
RxD/TxD
Inflator line 1
+
- 5
2
1
20
13
14
Air bag lamp
Communication/
diagnosis
Air bag
control
unit
Ground connection or open
Connector Pins
15
301
16

8B-6 SUPPLEMENTAL RESTRAINT SYSTEM(SRS)
AIR BAG MODULE
Air bag module is installed in the pad of steering wheel center and inflator is consisted of igniter, explosives, gas
generating material and bag. When crashed, the air bag control unit sends current to the air bag module through
squib line and this current ignites as ignition energy (6mJ) momentarily igniting explosives and bag will be inflated
by nitrogen gas protecting driver at the same and then deflates.
1 Air bag Module
2 Module Housing
3 Bag
4 Module Bracket
5 Retainer Ring
6 Inflator
7 Horn Switch
8 Backing Plate

SUPPLEMENTAL RESTRAINT SYSTEM(SRS) 8B-7
DIAGNOSIS
DESCRIPTION
Air bag control unit continuously controls system function as follows during ignition ON or driving.
- Recognition of collision
- Internal diagnosis
- External diagnosis
If recognize or detect defects, warning lamp will turn on. If there is danger of improper deployment, the system will
enter overall shutdown status and the air bag will not inflate.
Air bag control unit will store detected internal and external defects in the EEPROM.
System Control
Battery Voltage Check
Battery voltage will be monitored continuously. If voltage is out of normal operating range, all system diagnosis will
stop and warning lamp turn on.
Battery Voltage (V)
< 8.7
9 - 16
> 16.3
Function
System diagnosis stops and warning lamp turns on
Normal operation range
System diagnosis stops and warning lamp turns on
Squib Diagnosis
It checks not only high (4.50.5) or low (1.40.5) resistance but also short resistance (1- 10k) status between the
battery and ground to indicate defects in squib line by blinking warning lamp. Air bag control unit (AC4) can measure
squib resistance.
Warning Lamp Turning On
Air bag control unit detects system defects during ignition ON or driving and displays following 2 warning lamps.
- Warning lamp ON: internal defects of the air bag control unit
- Warning lamp blinking: higher resistance than standard in the squib line or short at the battery or ground,
Safety Function Check
It checks defects during operation of the arming sensor If the sensor is shorted for more than 2 seconds, the module
will enter overall shutdown mode.
Temperature Sensor
Function of the temperature sensor will be monitored continuously. If there is fault due to defective sensor or short,
the lamp will turn on and program will take calibration temperature (25) of collision conditions.
Power Supply
Airbag control unit operates in 9-16v and the characteristic of the system has backup condenser to supply the power
for max.150ms if there is power defect during collision.

8B-8 SUPPLEMENTAL RESTRAINT SYSTEM(SRS)
Energy Reserve System
Energy reserve system is consisted of condensor and energy switch and will check following items continuously
during system operation.
- High voltage
- Low voltage
- Low rating capacity
- Function of the energy reserve switch
If there is fault in the energy reserve system, warning lamp will turn on. And defects are found by continuous
checking of the condenser voltage, the system will enter overall shutdown status for safety reason.
Shutdown Switch
There is 1 energy shutdown switch in the system and it will be checked during start-up. And it also checks that
condenser is discharging properly. If shutdown switch is short, it will be detected during condensor voltage test.
If squib line fault is obvious, the warning lamp will turn on and the module will enter overall shutdown status.
Accelerometer Check
Accelerometer function will be checked during start-up. During operation, accelerometer off-set signal will be checked,
If there is fault, module will enter overall shutdown status.
ASIC Overheat
Module monitors upper side ASIC overheats continuously. If overheated, the module will enter overall shutdown
status.
Microprocessor Fault
Module checks EEPROM, ROM checksum and RAM during start-up. EEPROM tests checksum operation.
If RAM or ROM checksum is defective, module will not allow start-up continuously but will be re-set,
If EEPROM is defective, warning lamp will turn on and the module will enter overall shutdown status.
During operation, RAM will continuously verify the proper operation of temporary memory program data usage. If
there is fault, the module will enter overall shutdown status and the warning lamp will turn on.
Watchdog Test
Watchdog function will be tested in start-up. If there is fault during the test, warning lamp will turn on and the module
will enter overall shutdown status.