SRS
SRS
Published by
Chonan Technical Service Training Center
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To know the system components of SRS system.
Objectives
To understand the handling caution and replacement items for SRS system.
The SRS system for ED vehicle has an ACU supplied and developed by  TRW Gen 5.6 . This
ACU already introduced in VQ so please refer to VQ training manual for more detail information.
This manual will handle just for the basic information includes the parts components, its location
and some tips for warning lamp driving.
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1. Introduction
1.1 Major Components
- ACU: Airbag Control Unit (TRW GEN 5.6)
- FIS: Front Impact Sensors (LH & RH)
- SIS: Side Impact Sensors (LH & RH  front only)
- DAB: Single stage de-powered Driver Airbag Module
- PAB: Single stage de-powered Passenger Airbag Module
- SAB: Side Airbag (LH & RH - Front only)
- CAB: Curtain Airbag
- SPT: Seatbelt Pre-Tensioner with load limiters
- PAD (Passenger Airbag Deactivation) Switch  EU only
Depowered Airbag System (EU)
Single-PAB
PAD S/W
SIS
CAB
FIS
2. Component and Function
2.1 ACU(Airbag Control Unit)
ACU
Seat Belt Pre-tensioner
Single-DAB
ED Car has a MOBIS-TRW Gen 5.6 Airbag Electronic Control Unit (ACU). The ACU is designed
SAB
to handle the  Depowered functionality.
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Function :
- Crash Detection
- Activation of the front airbags, Curtain airbags and belt pre-tensioners
- Monitoring of the airbag restrain system
- Indicate system readiness and faults to the driver by means of a fault warning lamp
- Facilitate servicing capability via a serial diagnostic communication interface (scanner)
After power ON, the ACU shall behave as follows:
a) In the power OFF region, the ACU shall not perform any external and internal diagnostic since
the operation of the ACU is not guaranteed. If the ACU is operational, it shall attempt to
command the AWL ON.
b) The ACU shall perform internal diagnostics only if thirty consecutive (10ms sample rate)
voltage reading are within or above the  Vbatt too low range. If the ACU doesn t detect a
voltage reading within the  normal operating range for 4sec, then  Vbatt too low or  Vbatt too
high is qualified.
c) The ACU shall perform external diagnostics only if thirty consecutive (10ms sample rate)
voltage readings are within the  normal operating range.
ACU shall try to deploy corresponding firing squib(s) in case of crash detection during power
disturbance region.
Operational Temperature: -40 to 85 °C
Storage Temperature: -40 to 90 °C
Connector PIN Layout :
13 14 15 16 17 18 19 20 21 22 23 24 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
1 2 3 4 5 6 7 8 9 10 11 12 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17
Connector A Connector B
Shorting bar clip
Pin Assignment :
AECU Cavity A (J1A-XX) ACEU Cavity B (J1B-XX)
Pin # (IP) Pin # (Body)
1 Ignition 1 Squib_9_L / Drv Side
2 ISO9141 (K-Line) / CANH 2 Squib_9_H / Drv Side
3 CANLO 3 Squib_10_H / Pass Side
4 SeatBelt Reminder 4 Squib_10_L / Pass Side
5 Crash Out 5 Squib_12_L / Pass curtain
6 PAD Lamp 1 6 Squib_12_H / Pass curtain
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7 Unused (GND) 7 Squib_11_H / Drv curtain
8 DSI_CHANNEL2- FIS Pass LOW 8 Squib_11_L / Drv curtain
9 DSI_CHANNEL2+ FIS Pass HIGH 9 Squib_13_L / Drv Rear curtain
10 DSI_CHANNEL1- FIS Drv LOW 10 Squib_13_H / Drv Rear curtain
11 DSI_CHANNEL1+ FIS Drv HIGH 11 Squib_14_H / Pass Rear Curtain
12 PAD Switch 12 Squib_14_H / Pass Rear Curtain
13 AIRBAG WARNING LAMP 13 Squib_3_L / Drv Frontal Pret
14 GND 14 Squib_3_H Drv Frontal Pret
15 Squib_2_L / Passenger 1st Stage 15 Squib_4_H Pass. Frontal Pret
16 Squib_2_H / Passenger 1st Stage 16 Squib_4_L Pass. Frontal Pret
17 Squib_1_H / Driver 1st Stage 17 DR_BUCKLE sensor
18 Squib_1_L / Driver 1st Stage 18 PASS_BUCKLE
19 Squib_8_L / Passenger 2nd 19 DRV Seat Position
20 Squib_8_H / Passenger 2nd Stage 20 PASS Seat Position
21 Squib_7_H / Driver 2nd Stage 21 DSI_CHANNEL3- SIS Drv LOW
22 Squib_7_L / Driver 2nd Stage 22 DSI_CHANNEL3+ SIS Drv HIGH
23 Squib_16_H / Drv rear Side 23 DSI_CHANNEL4- SIS Pass LOW
24 Squib_16_L / Drv rear Side 24 DSI_CHANNEL4+SIS Pass HIGH
25 Unused (GND)
26 Occupant Classification(ISO9141)
27 Squib_15_H / Pass Rear Side
28 Squib_15_L / Pass Rear side
29 Squib_5_L / Drv 2nd Stage Pret
30 Squib_5_H Drv 2nd Stage Pret
31 Squib_6_H / Pass 2nd Stage Pret
32 Squib_6_H / Pass 2nd Stage Pret
Connector shorting bar present
A/D Count = 49 A/D Count = 79 A/D Count = 164
A/D Count = 49 A/D Count = 79 A/D Count = 164
Normal Operating Range
Normal Operating Range
5.19 5.95 8.02 8.99 16.05 17.63
5.19 5.95 8.02 8.99 16.05 17.63
Grey Vbatt Grey Grey Vbatt
Grey Vbatt Grey Grey Vbatt
Power off Guaranteed Range
Power off Guaranteed Range
Zone too low Zone Zone too high
Zone too low Zone Zone too high
4 sec 4 sec
4 sec 4 sec
4 sec 4 sec
4 sec 4 sec
4 sec 4 sec
4 sec 4 sec
 Vbatt too low  Vbatt too low
 Vbatt too low  Vbatt too low
 Vbatt too high  Vbatt too high
 Vbatt too high  Vbatt too high
DTC qualified DTC dequalified
DTC qualified DTC dequalified
DTC dequalified DTC qualified
DTC dequalified DTC qualified
Range Name Nominal voltage Fault Qualification/Dequalification
Power off Ign < 6 Qualification/Dequalification of all internal and external
DTC s are suspended (qualification / dequalification
counter frozen)
Vbatt too low 6 < Ign < 9 " Qualification/Dequalification of external DTC s are
performed normally until  Vbatt too low DTC is
qualified.
" Qualification/Dequalification that are performed
regardless of Ignition voltage level in this range
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consist of DTC related to:
1. RAS diagnostics
2. Internal diagnostics
3. Crash related
4. SIFA inputs
" OCE communication DTC
qualification/dequalification are disabled as soon as
ignition is detected in this range without waiting for
 Vbatt too low to be qualified.
Normal Operating 9 < Ign < 16 Qualification/Dequalification of all internal and
range external diagnostics are performed normally in this
range.
Note: Ignition has to be in this range for 3s (Ä… 10%)
before OCE communication
Qualification/Dequalification diagnostics are performed.
Vbatt too high Ign > 16 " Qualification/Dequalification of external DTC s are
performed normally until  Vbatt too hi DTC is
qualified.
" Qualification/Dequalification that are performed
regardless of Ignition voltage level in this range
consist of DTC related to:
1. RAS diagnostics
2. Internal diagnostics
3. Crash related
4. SIFA inputs
2.2 Frontal Airbags
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Resistance (©): 1.7~2.3 (for both DAB & PAB)
2.4 SAB (Side Air Bag) & CAB (Curtain Airbag)
Resistance (©): 1.7~2.3 (for both SAB & CAB)
2.5 SPT(Seatbelt Pre Tensioner)
When a vehicle has crashed with a certain
degree of frontal impact, the gas generator is
made to ignite by the electrical firing signal from
SRSCM.
Gas from the gas generator causes
movement of the piston in the manifold case
(cylinder), which operates a rack gear. Finally
the webbing is retracted by the rotation of the
spool. Therefore the seat belt pretensioner
helps to reduce the severity of injury to he front
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occupant by retracting the seat belt webbing to
prevent the occupant from moving forward and hitting the steering wheel or instrument panel when
the vehicle is crashed. On the other hand, the buckle pre-tensioner is not applied in ED.
2.6 FIS (Front Impact Sensor) & SIS(Side Impact Sensor)
The front impact sensor (FIS) is installed on the upper of the side panel in Front End Module (FEM).
They are remote sensors that detect acceleration due to a collision at its mounting location. The
primary purpose of the Front Impact Sensor (FIS) is to provide an indication of a collision.
The Front Impact Sensor(FIS) sends acceleration data to the SRSCM.
The Side Impact Sensor (SIS) system consists of two front SIS which are installed in the center pillar
(LH and RH) and two rear SIS which are installed in the rear pillar (LH and RH). They are remote
sensors that detect acceleration due to collision at their mounting locations. The primary purpose of
the Side Impact Sensor (SIS) is to provide an indication of a collision. The Side Impact Sensor (SIS)
sends acceleration data to the SRSCM.
TRW-RASII (Remote Acceleration Sensor)
The RASII shall be used as a remote crash sensing
module providing acceleration and status data over
the DSI bus to the ACU. The main components of
RASII assembly are the 250 acceleration sensor and
the Orion ASIC. This ASIC provides power for the
accelerometer and for itself, accelerometer
measurement and communication between the
remote acceleration sensor and the central air bag
control module in the vehicle.
The Orion ASIC obtains analog data from the
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Sensor Part for SIS (TRW RAS II)
SRS
accelerometer, converts it to digital information, and
then transmits the acceleration data over the DSI
interface bus when commanded by the central air bag
control module in the vehicle.
The RASII is intended to directly interface with a DSIP ASIC inside the ACU. Power and data
communications are performed on one interface conductor between the RASII and ACU. A second
common / ground conductor completes the interface. For 4 pin RASII a second set of Power /
Communications and common / ground conductors are used to interface to a second RASII.
RASII Locations and Acceleration Ranges
Accel. Range
RAS Application Location Options Axis
Options
Frontal impact crush zone sensor Frontal Impact Crush Zone Ä… x axis Ä… 250g
Side impact Crush Zone Ä… z axis Ä… 250g
RASII component block diagram
.
2.8 PAD (Passenger Airbag Deactivation) Switch
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(1) Purpose for Installation
The PPD sensor used for detecting that any passenger is or not in convention is removed. Instead,
the ON/OFF S/W is installed inside of the glove box, so that the driver can determine that the PAB
may be unfold or not.
The ACU shall be capable of sensing the following PAD switch status:
1. PAD switch in enable position
2. PAD switch is disable position
3. PAD switch unstable
4. Open / Short to Battery
5. Short to Ground
BODY HOUSING
COVER
REAR COVER
ROTOR PCB
SPRING HOLDER
Pin No Description
1 Ignition 1
2 Earth- Glove Box
Ground  ACU I/ F
3
4 ACU Interface Line
Connector type and pin Layout
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PAB ON/OFF SWITCH WIRE DIAGRAM
(2) PAD switch Resistive Load
The ACU shall sample the PAD switch
periodically(50ms). The ACU shall change
the status of PAD switch only after 5
consecutive samples with a status change
have been received. If a stable input is not
achieved within 20 samples, then instability
DTC shall be qualified.
The ACU shall be capable of sensing the following PAD switch statuses:
1. PAD switch in enable position
2. PAD switch is disable position
3. PAD switch instable
4. Open/ Short to Battery
PAD Switch Status Resistances between PIN #3 and #4
Enabled 1010 ohm Ä… 10%
Disabled 330 ohm Ä… 10%
5. Short to Ground
6. Defect
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4. Electrical Interface Requirements
4.1 Squibs
The ACU is designed to provide electrical energy back up a maximum 12 squibs for up to 150msec.
This allows for a maximum of one squib shorted.
4.2 squib wires shorted to GND
If any one of the twelve squibs that are protected by backup energy is shorted to ground, sufficient
energy will still be provided to the other eleven squibs to maintain firing capability.
4.3 GEN 5.6 Firing Loops & Diagnosis Currents
The ACU shall be capable to deploy all backed up firing loops up to at least 150ms after IGN has
been disconnected. The firing and diagnostic current requirements for a specific platform is defined in
corresponding application addendum.
4.5 Squib Diagnostics
The ACU shall be capable of detecting when any of the squibs are shorted to battery or ground, or
open circuit. The ACU shall record such a condition.
The largest current that the ACU will pass through the squib is the pulse used for measuring the
resistance of the squib and wiring. The level of the pulse corresponds to 20mA to 32mA. Based on a
good squib range of 1.6ohms to 6.1 ohms (worst case), this will give a differential voltage across to
squib of 32mV to 195mV. The ACU will pass other smaller current pulse to diagnose faults of the
squib ASIC, and their interconnections.
5. Outputs
5.1 Airbag (SRS) Warning Lamp Operations
(Active fault or historical fault counter is greater or equal to 10)
(Normal or historical fault counter is less than 10)
During start-up phase, the warning lamp shall be commanded ON for 6 seconds (+/- 10 %) and
OFF for 1 second. Thereafter, the lamp shall be commanded ON only under the following cases:
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1. Lamp latch condition
2. Qualified fault is present
3. During communication with service tool.
5.2 SRS Warning Lamp latch
The SRS warning lamp shall be latched ON if certain conditions are present. Some lamp latch
conditions can be cleared by the service tool while others require the replacement of the ACU.
Below is a description of each condition:
Lamp Latch condition that can be cleared by the service tool:
1. 10 different external faults except Vbatt too low are qualified in the ACU.
2. A certain external fault except Vbatt too low has qualified 10 times in the ACU.
3. Belt pretensioner only firing (<6 times)
4. Rear crash detected DTC is qualified
5. Instability DTC for Seat Buckle, Seat Position, and PAD Switch.
Lamp Latch condition that can not be cleared by the service tool.:
1. Any internal DTC is qualified.
2. Belt pretensioner only firing (e"6 times)
3. Any airbag deployment DTC is qualified
5.3 ACU behavior during service communication
During the service or repair communication process the ACU shall behave as follows:
Ć% ACU shall turn its SRS warning lamp ON as long as the communication between ACU and Service
tool is active. . . . .
Ć% Internal diagnostics process of ACU and external diagnostic process of related system shall not be
altered and shall be carried out as it is in normal operating condition.
1. The crash discrimination and firing shall be suppressed to prevent inadvertent deployment
during service communication.
Ć% The SRS warning lamp shall not be turned OFF even though stored faults memory is erased via
service tool unless the communication process is completed or terminated.
Ć% The ACU shall consider the communication process as completed if:
1. A stop communication request from service tool is received
2. The communication is timed out (300 ms)
Under the above conditions, the ACU shall reset without supply power on/off. The SRS warning
lamp shall go through normal Phase-up.
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5.4 Passenger Airbag Disable (PAD) Indicator Operation
The ACU shall be designed with circuitry and software to drive either a PAD or a tell-tale lamp.
PAD lamp will be used for de-powered systems. For the PAD indicator circuitry to function properly
both the ACU and PAD Indicator shall be sourced from the same ignition line.
During phase-up, the PAD indicator shall be commanded ON for 4 seconds (+/- 10 %) and OFF for 3
second. Thereafter the lamp will be turned on as long as the PAD switch is in the disabled position.
PAD Lamp operation during Phase-up
5.5 Crash Output
When a deployment occurs, or when a rear crash is detected, the Crash Output is activated. The
Crash Output will have the capability to sink a minimum of 15 mA to ground from Vbatt, and a 1.2
k&! source or from Vcc and a 470 &! source, under normal operating conditions. The waveform of
the output will be to activate the output within 100 ms (Ä… 10%) of the airbag or pretensioner
deployment, or rear crash detection and hold the output for 200 ms, Ä… 10%. The purpose of this
output is to signal the BCM/ETAC module in the vehicle to unlock the vehicle doors. If a crash
output signal is in progress, a second crash output signal will not be sent unless the first one is
completed.
The ACU doesn t perform diagnostics on the crash output function. In addition, the failure
handlings such as circuit failure between ACU and BCM, noise injection in crash output command
line that may induce invalid message shall be handled by BCM not ACU
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Crash Output Signal
Crash Output interface to the ACU
6. System Diagnostics and Fault Handling
6.1 Fault Recognition
The ACU shall start the fault management during the prove-out period. The ACU qualifies a fault
when it has detected that fault for the qualification period or number of occurrences. The ACU shall
store the fault codes onto EEPROM and turn ON the SRS warning lamp. RAS sensor fault are tested
at a more rapid rate than other faults ; their sample rate is based on the algorithm update rate. Some
internal fault are only tested during phase-up.
After a fault is qualified, the fault is de-qualified when that fault has been not detected for the de-
qualification period. If no qualified faults are present, the warning lamp turns off. Diagnosis of firing
devices is suspended during the deployment process, but resumes thereafter. Faults for devices
which were fired in a crash will be suppressed.
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6.2 Fault Handling
An internal fault is a fault inside of the ACU (i.e. accelerometer, microcomputer power supply, or
watch dog),and is not erasable. An external fault is a fault outside of the ACU (i.e. RAS II, Occupant
Detection, squibs), and is erasable. Once any internal fault has been qualified, the corresponding fault
record in non-volatile memory of the ACU shall not be erasable. All internal faults shall not de-qualify.
The ACU denounces all faults to make sure that no erroneous faults are recorded. The ACU shall
set qualified faults to historic faults as soon as the active fault conditions are recovered and
disqualified. At this time, the warning lamp shall be turned off and historic fault code and
corresponding fault information shall be stored in EEPROM within the ACU.
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