Passive restraint systems like airbags and seatbelts were developed in the 1970s and required by law in the late 1980s to protect unbelted passengers. Airbags deploy at around 200mph to stop occupants moving at high speeds without killing them. Supplemental restraint systems (SRS) like airbags supplement seatbelts and require them to be buckled for effective protection. SRS components include airbags, sensors, an diagnostic module that monitors readiness and controls airbag deployment. Upon crash detection, airbags inflate within 40 milliseconds to cushion occupants.

1. SRS Systems

3. BANG!!!
BANG!!!

5. Supplemental Restraint
Systems
Early studies found that a very high
percentage of drivers were not using seat
belts, resulting in ejection from vehicles
and severe trauma injuries
Passive (no driver action) restraints
developed in early 70’s and required by
law in late 80’s to protect vehicle
passengers when unbelted in vehicle

6. Supplemental Restraint
Systems
Passive Seat Belts
 Lap belts and shoulder belts
Air Bags
 Driver side and passenger side
 Early air bags 100% deployment power
 60/40 two stage as 100% too powerful in
some situations
 Both systems SUPPLEMENT Seat Belts
 Neither will work affectively without the seat
belts buckled

7. Passive Seat Belt System
Features
Uses a control module to monitor
operation
The module receives input from various
position and limit switches
The module activates a motor to
position the seat belt properly on the
driver’s shoulder

8. Passive/Automatic Seat Belt
Can be motor driven
and move from A
pillar to B pillar
Can be connected to
door (obsolete)

9. Passive Seat Belt
Motor & Cable
Popular in 80’s and 90’s
Motor located behind B
Pillar
Track runs from A to B
Pillar
Limit Switches located
in Both A and B Pillar
Tend to wear from dirt in
track, stopping belt in
mid-travel

10. Seat Belt Pretensioners
Used to tighten the
seat belt and shoulder
harness around the
occupant when the air
bag is deployed
May be mounted on
the buckle side or
retractor side of the
seat belt

11. Air Bag Safety
ALWAYS FOLLOW MFG TESTING
PROCEDURES!
CARRY AIR BAG ASSEMBLIES
FACE DOWN
ALWAYS DISARM SRS SYS PER
MFG BEFORE SERVICING
RELATED SYSTEMS
NEVER TAP INTO YELLOW WIRE
LOOMS

12. Air Bag Physics
Air bags deploy at about 200mph
Must stop a person moving 90
ft/sec in about 5 feet…without
killing the person!
LOUD!!!
 Jet engine @ 100’, gunshot 140dB
 Air bag deployment 165dB
 Death of hearing tissue 180dB

13. Want more physics?
Stand-by for more
pain…

15. Air Bag Locations
Driver (steering wheel) and passenger
front (dash)
Side air bag (side of seat)
Side-torso
Side tubular or curtain (above head)
Rear curtain
Center
Knee
Seat belt

16. Air Bag Locations

17. Motorcycle SRS Systems

18. Personal SRS Systems

19. Aviation SRS Systems

20. Runway safety for top fashion
models (can’t be too careful in
front of all those cameras…)
Available in Blonde, Brunette & Redhead

21. …or when you absolutely,
positively have to be at another
planet in one piece!

22. Pedestrian SRS Systems
Used to prevent
pedestrian head injury
In production now in
Asian markets
Was to be in US in
2012

23. REMEMBER..
Disarm air bags before servicing related parts!
 May need to wait up to 10 minutes for capacitors to
discharge
You must use torque wrench to torque sensors
and modules. A loose sensor can give false
acceleration readings.
Do NOT use air tools near sensors!
Live air bags must be deployed before sending
back. Don’t share the love.

24. Driver’s side Air Bag

25. Multi-Stage Air Bag Features
Uses two squibs to control the rate of
inflation
In a minor accident, only one squib is
deployed
As the severity of deceleration forces
increases, the second squib will deploy

26. 60/40 Air Bag Inflator
In medium speed deceleration, 60%
charge is used
In high speed deceleration, both 60% and
40% charges are
used for full
occupant protection

27. Two Stage SRS connectors

28. Passenger Side Air Bag
Features
They are much larger than driver’s side
bags
They deploy with the driver’s side bag,
on most systems
Many systems have cut-off switches
 Usually on trucks where there is no back
seat
 Was add-on kit from Ford in the late 90’s
 Most new vehicles now equipped w/switch

29. Passenger Side Air Bag

30. Child Safety Switching

31. Side Impact Air Bag Features
Are single stage hybrid design
Can be located in various
places, depending on the
vehicle
Deploy separately from the
front air bags
May have a separate
control module

32. Curtain Side Air Bag

33. Air Bag System Common
Components

34. Air Bag System Common
Components
Diagnostic Module
 Constantly monitors the readiness of the
SRS electrical system
Crash Sensors
 Used to signal that the vehicle is involved
in a crash
Seat Weight/Position Sensors
 Inform module of passenger position &
weight

35. Diagnostic Module Functions
Controls the instrument panel warning
lamp
Continuously monitors all air bag
components
Controls air bag diagnostic functions
Provides an energy reserve to deploy air
bag if battery voltage is lost during a
collision

36. SRS Module
Note Arrow shows
mount direction

37. Diagnostic Module Self Test
When key is turned on the SRS module
performs the following checks
 Checks reserve power from capacitor
 Checks bulb condition
 Checks crash sensors for shorts opens or
grounds
 Checks air bag resistance
 If all checks are okay, the system is active
 Stores crash information for retrieval later
Very controversial!

38. Types of Sensors
Mass-type sensor
 Contains gold-plated contacts and a gold-
plated ball
Cash value 2 cents
 When vehicle is involved in a crash, the
ball rolls forward and closes the switch
contacts

40. Accelerometer sensor
 Contains a piezoelectric element that is
distorted in a crash
 Generates an analog voltage in relation to
the severity of the crash

41. Side Impact Sensor
Mounted in “B” pillar between front and
rear seat rows
Senses side impact, begins process of
inflating seat and curtain air bags

42. Seat Weight Sensor

43. OPDS Side Impact Air Bag

44. Air Bag On/Off Switches
May be manually controlled when a
child is sitting in the passenger seat
Some systems automatically detect
when a child seat is in the passenger
side of the front seat
 Sensors must be calibrated when any
portion of the seat is replaced.
 Accident may cause floor pan damage
making re-calibration necessary

45. Calibrating with Special Service
Tool: Plastic Butt

46. Typical Air Bag Deployment
Sequence
When a crash occurs, the arming sensor
will close first, then the crash sensors will
close
 The arming sensor must “set” first
 Then crash sensors tell SRS module
location/severity of crash

47. Typical Air Bag Deployment
Sequence
Within 40 milliseconds, the igniter module
burns the propellant and inflates the bag
Within 100 milliseconds, the air bag starts
to deflate
Within 2 seconds, the air bag is completely
deflated

48. By-Products of Inflator Module
Combustion
Nitrogen - 99.2%
Water - 0.6%
Hydrogen - 0.1%
Sodium oxide - less than 1/10 of 1 part per
million (PPM)
Sodium hydroxide - very minute quantity
Nothing that will make you sick if you touch
it…besides it just saved your life!

49. End SRS Systems