SSANGYONG MUSSO 1998 Workshop Repair Manual

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.

SUPPLEMENTAL RESTRAINT SYSTEM(SRS) 8B-9
Diagnosis
Air bag control unit diagnoses each function in the intervals of 250ms - 20 sec. during start-up or driving to prevent
unwanted air bag deployment. If there is defect, it turns on or blinks warning lamp to indicate defects in the air bag
system to the driver. And fatal defect is found, air bag control unit enters overall or partial shutdown status and fault
code will be stored.
Air bag control unit diagnoses following items.
- Ignition TR
- Acceleration
- Microprocessor, RAM and ROM
- Watchdog
- Shutdown Switch
Diagnosis Condition Diagnosis Items
Start-up (ignition ON)
During Driving
Lamp Blinking Mode
There are 2 kinds of blinking mode
1. When system internal fault is found, the lamp will stay on.
2. The lamp will blink according to external fault and there are 2 blinking codes.
Blinking code 1 (Squib resistance fault in the driver’s air bag squib line)
Blinking code 2 (Squib short on plus and minus in the air bag squib line)
Lamp blinking code is as follows. The last blinking will be within 0.5 sec. and 1 cycle of blinking will be repeated every
5 seconds.
Blinking Code 1
(Sec.) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
Blinking Code 3
(Sec.) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
- Squib resistance
- Squib line short to battery and ground
- Energy reserve system
- Lamp output
- Battery voltage
- ASIC communication
- Arming sensor
- ASIC overheating
- RAM and W/D
- EEPROM

8B-10 SUPPLEMENTAL RESTRAINT SYSTEM(SRS)
1. Position the ignition switch to ‘OFF’.
2. Connect the harness connector of scanner to the diagnosis
socket in engine compartment.
3. Turn the ignition switch to ‘ON’ position.
4. Select “Electronic control vehicle diagnosis” from function
selection display and press ‘Enter’.
5. Select “Musso (’98 model year)” from vehicle model
selection display and press ‘Enter’.
6. Select “Electronic air bag” from control system selection
display and press ‘Enter’.
7. Select “Self-diagnosis” from diagnosis item selection display.
Notice
Check sensor value of output display, if necessary.
8. Determine the fault code and trace defective component.
Notice
Refer to self-diagnosis list.
SELF DIAGNOSIS

SUPPLEMENTAL RESTRAINT SYSTEM(SRS) 8B-11
Self-Diagnosis List
Fault
CodeDefectsService Hint
01 Driver’s squib (+) side No. 1
lShort of (+) side No. 1 in the driver’s squib circuit.
lCheck connection of connector.
lCheck the ECU.
Appli-
cation
02 Driver’s squib (+) side No. 2lShort of (+) side No. 2 in the driver’s squib circuit.
lCheck connection of connector.
lCheck the ECU.
X
03 Driver’s squib (+) side No. 3lShort of (+) side No. 3 in the driver’s squib circuit.
lCheck connection of connector.
lCheck the ECU.
X
04 Driver’s squib (+) side No. 4X
05 Driver’s squib ground (-) side No. 1lShort of ground side No. 1 in the driver’s squib
circuit.
lCheck and replace the ECU.
06 Driver’s squib ground (-) side No. 2lShort of ground side No. 2 in the driver’s squib
circuit.
lCheck and replace the ECU.
X
07 Driver’s squib ground (-) side No. 3lShort of ground side No. 3 in the driver’s squib
circuit.
lCheck and replace the ECU.
X
08 Driver’s squib ground (-) side No. 4lShort of ground side No. 4 in the driver’s squib
circuit.
lCheck and replace the ECU.
X
09 Energy shutdown switch No. 1lAir bag control unit internal defects.
lCheck and replace the ECU.
10 Energy shutdown switch No. 2lAir bag control unit internal defects.
lCheck and replace the ECU.
X
11 Energy shutdown switch No. 3lAir bag control unit internal defects.
lCheck and replace the ECU.
X
12 Energy shutdown switch No. 4lAir bag control unit internal defects.
lCheck and replace the ECU.
X
13 Ignition switch wire No. 1lAir bag control unit internal defects.
lCheck and replace the ECU.
14 Ignition switch wire No. 2lAir bag control unit internal defects.
lCheck and replace the ECU.
X
15 Ignition switch wire No. 3lAir bag control unit internal defects.
lCheck and replace the ECU.
X
16 Ignition switch wire No. 4XlAir bag control unit internal defects.
lCheck and replace the ECU.

8B-12 SUPPLEMENTAL RESTRAINT SYSTEM(SRS)
Fault
CodeDefectsService HintAppli-
cation
17 Squib No. 1 resistance
18 Squib No. 2 resistanceX
19 Squib No. 3 resistanceX
20 Squib No. 4 resistanceX
21 Squib No. 1 resistance
22 Squib No. 2 resistanceX
lDriver’s squib resistance is higher than standard
(4.5±0.5W).
lCheck related circuits for open/short.
lCheck connection of connector.
lCheck the ECU.
lReplace the squib wire.
lPlus side short : 7k, ground side short : 6kW.
lDriver’s squib resistance is higher than standard
(4.5±0.5W).
lCheck related circuits for open/short.
lCheck connection of connector.
lCheck the ECU.
lReplace the squib wire.
lPlus side short : 7k, ground side short : 6kW.
lDriver’s squib resistance is higher than standard
(4.5±0.5W).
lCheck related circuits for open/short.
lCheck connection of connector.
lCheck the ECU.
lReplace the squib wire.
lPlus side short : 7k, ground side short : 6kW.
lDriver’s squib resistance is higher than standard
(4.5±0.5W).
lCheck related circuits for open/short.
lCheck connection of connector.
lCheck the ECU.
lReplace the squib wire.
lPlus side short : 7k, ground side short : 6kW.
lDriver’s squib resistance is lower than standard
(1.4±0.3W).
lCheck related circuits for open/short.
lCheck connection of connector.
lCheck the ECU.
lReplace the squib wire.
lPlus side short : 7k, ground side short : 6kW.
lDriver’s squib resistance is lower than standard
(1.4±0.3W).
lCheck related circuits for open/short.
lCheck connection of connector.
lCheck the ECU.
lReplace the squib wire.
lPlus side short : 7k, ground side short : 6kW.
23 Squib No. 3 resistanceXlDriver’s squib resistance is lower than standard
(1.4±0.3W).
lCheck related circuits for open/short.
lCheck connection of connector.
lCheck the ECU.
lReplace the squib wire.
lPlus side short : 7k, ground side short : 6kW.

SUPPLEMENTAL RESTRAINT SYSTEM(SRS) 8B-13
Fault
CodeDefectsService HintAppli-
cation
24 Squib No. 4 resistance
X
25 Energy reserve No. 1 voltage
26 Energy reserve No. 2 voltageX
27 Energy reserve No. 3 voltageX
28 Energy reserve No. 4 voltageX
29 Energy reserve No. 5 voltage
30 Energy reserve No. 6 voltage
31 Energy reserve No. 1 current off
capacity
32 Energy reserve No. 2 current off
capacityX
33 Energy reserve No. 3 current off
capacityX
34 Energy reserve No. 4 current off
capacityX
35 Energy reserve No. 5 current off
capacity
36 Condensor voltage
37 Collision times checksum
lDriver’s squib resistance is lower than standard
(1.4±0.3W).
lCheck related circuits for open/short.
lCheck connection of connector.
lCheck the ECU.
lReplace the squib wire.
lPlus side short : 7k, ground side short : 6kW.
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.
4 1 Major USAlAir bag control unit internal defects.
lCheck and replace the ECU. 38 Driver’s acceleration sensor
39
Driver’s acceleration sensor off-set
40 Arming sensor
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.

8B-14 SUPPLEMENTAL RESTRAINT SYSTEM(SRS)
Fault
CodeDefectsService HintAppli-
cation
42 Over heat
4 3 SENS
44 Standard band gap
45 Temperature sensor
46 Warning lamp
47
Battery voltage
49 Fault code list
5 0 USA communication
51 LSA communication
52 No EEPROM program
53 EEPROM checksum
5 4 EEPROM map
55 External watchdog 1
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.
lOpen/short in the warning lamp circuit.
lCheck related circuits for open/short.
lCheck connection of connector.
lCheck the ECU.
lPower wire voltage is out of standard voltage (9
- 16V).
lCheck the battery for voltage and charging.
lCheck related circuits for open/short.
lCheck connection of connector.
lCheck the ECU.
lAir bag control unit internal defects.
lCheck the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.
56 Arming sensor-no close
57 RAM check
5 8 System
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.
59 External watchdog 2
6 0 Pulse
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.

SUPPLEMENTAL RESTRAINT SYSTEM(SRS) 8B-15
Fault
CodeDefectsService HintAppli-
cation
127 Collision signal
128 Collision number
lAir bag control unit internal defects.
lCheck and replace the ECU.
lAir bag control unit internal defects.
lCheck and replace the ECU.

8B-16 SUPPLEMENTAL RESTRAINT SYSTEM(SRS)
CIRCUIT DIAGRAM