Automotive Electrical and Electronic Systems Classroom Manual Fifth Edition Update by John F. Kershaw
Body Accessory Systems Operation 349CANBATTERY (+)AIR BAGSGROUND (-)O-RINGS SEALSSAFINGSENSORCRASHSENSORSSENSING MASSELECTRICALCONTACTSFigure 15-52.Operations)Safing sensor. (GM Service and PartsBIAS MAGNETFRONT OF CARMOUNTINGPLATESteeringWheelWiringShieldFigure 15-51.SRS sensors. (DaimlerChrysler Corporation)only. Although the design of individual systemsvaries, the vehicle must be traveling a minimumof 12–28 mph before the system is armed andready for deployment.All the sensors use some type of inertia switchingmechanism that provides for the breakaway ofa metal ball from its captive magnet. This functioncauses a signal to activate a portion of the deploymentprogram set up in the control processor. Thesystem is still capable of directly applying batterypower to the squib or detonator. At least two sensors,one safing sensor and one front crash sensor,must be activated to inflate the air bag.Safing SensorsAn integrated version of this network includes asafing sensor (Figure 15-52), sometimes attachedto the original crash sensor. This device confirmsthe attitude and magnitude of the frontal decelerationforces and offers the microprocessor a secondopinion before actual deployment. This is allit takes to complete the firing sequence, and thebag will deploy.Wiring HarnessThe wiring harness connects all system componentsinto a complete unit. The wires carry theelectricity that signals the air bag to inflate. Theharness also passes the signals during the selfdiagnosissequence.Figure 15-53.Corporation)RetainerRingInflaterIgniterMountingAssemblyPlateSIR or Air Bag Readiness LightThis light lets the driver know the air bagsystem is working and ready to do its job. Thereadiness lamp lights briefly when the driverturns the ignition key from OFF to RUN. A malfunctionin the air bag system causes the lightto stay on continuously or to flash, or the lightmight not come on at all. Some systems havea tone generator that sounds if there is a problemin the system or if the readiness light isnot functioning.Air Bag ModuleModuleLinerBagAssemblyAir bag module. (DaimlerChryslerTrimCoverAssemblyThe bag itself is composed of nylon and issometimes coated internally with neoprene. Allthe air bag module (Figure 15-53) componentsare packaged in a single container, which ismounted in the center of the steering wheel orin the dash panel on the passenger side. Theentire assembly must be serviced as one unitwhen repair of the air bag system is required.The air bag module is made up of the followingcomponents.
350 Chapter FifteenElastomericSealIgniter andHousing AssemblyFilter/CoolingMediaFigure 15-54.Operations)IntensifierAssemblyGenerantGenerantHousingIgniter assembly. (GM Service and PartsAir BagModuleSteering WheelVibration DamperFWD AutomaticTransmission OnlyClock SpringElectricalConnectorSteeringColumnFigure 15-55. Liner and steering wheel trim cover.(GM Service and Parts Operations)Igniter Assembly (Figure 15-55)Inflation of the air bag is caused by an explosiverelease of gas. For the explosion to occur, achemical reaction must be started. The igniterassembly does this when it receives a signalfrom the air bag monitor. Actually, the igniter isa two-pin bridge device: When the electricalcurrent is applied, it arcs across the two pins,creating a spark that ignites a squib (canisterof gas) that generates zirconic potassium perchlorate(ZPP). This material ignites the propellant.Some newer model air bags now use solidpropellant and argon. This gas has a stablestructure, cools more quickly, and is inert aswell as non-toxic.Inflator ModuleThe inflator module contains the ZPP. Once ittriggers the igniter, the propellant charge is progressive,burning sodium azide, which convertsto nitrogen gas as it burns. It is the nitrogen gasthat fills the air bag.Almost as soon as the bag is filled, the gas iscooled and vented, deflating the assembly as thecollision energy is absorbed. The driver is cradledin the envelope of the supplemental restraintbag instead of being propelled forward to strikethe steering wheel or be otherwise injured byfollow-up inertia energy from seat belt restraintsystems. In addition, a certain degree of facialprotection against flying objects is obtained justwhen it is needed.It is important to remember that only the tandemaction of at least one main sensor and a safing sensorinitiates safety restraint system activation. Themicro-controller also provides failure data andtrouble codes for use in servicing various aspectsof most systems.Mounting Plate and Retainer RingThe mounting plate and retainer ring attach theair bag assembly to the inflator. They also keepthe entire air bag module connected to the steeringwheel.Liner and Steering Wheel Trim Cover(Figure 15-56)The liner houses the air bag; the trim cover goesover the exterior of the steering wheel hub.Passenger-side air bags are very similar in designto the driver’s unit. The actual capacity of gasrequired to inflate the bag is much greater becausethe bag must span the extra distance between theoccupant and the dashboard at the passenger seatinglocation. The steering wheel and columnmake up this difference on the driver’s side.WARNING: When the air bag is deployed, a great deal of heat is generated. Although the heatis not harmful to passengers, it may damage the clock spring electrical connector.When replacinga deployed air bag module, examine all of the electrical connections for signs of scorchingor damage. If damage exists, it must be repaired.
- Page 311 and 312: 298 Chapter ThirteenFigure 13-28. S
- Page 313 and 314: Figure 13-32.300A wiring schematic
- Page 315 and 316: 302 Chapter ThirteenFigure 13-34.GM
- Page 317 and 318: 304 Chapter Thirteenc. VFDd. CRT14.
- Page 319 and 320: 306 Chapter FourteenFigure 14-1. A
- Page 321 and 322: 308 Chapter FourteenFigure 14-7.Low
- Page 323 and 324: 310 Chapter FourteenFigure 14-12. T
- Page 325 and 326: 312 Chapter FourteenSome two-speed
- Page 327 and 328: 314 Chapter FourteenReview Question
- Page 329 and 330: 316 Chapter FifteenHEATING ANDAIR-C
- Page 331 and 332: 318 Chapter Fifteencoil. The switch
- Page 333 and 334: 320 Chapter Fifteenthe programmer t
- Page 335 and 336: 322 Chapter FifteenFigure 15-12.BCM
- Page 337 and 338: 324 Chapter FifteenFigure 15-14. Ca
- Page 339 and 340: 326 Chapter Fifteena qualified radi
- Page 341 and 342: 328 Chapter FifteenFigure 15-22. De
- Page 343 and 344: 330 Chapter FifteenFigure 15-25. Ty
- Page 345 and 346: 332 Chapter FifteenFigure 15-30.Hea
- Page 347 and 348: 334 Chapter Fifteenthe heated seat
- Page 349 and 350: 336 Chapter Fifteen• Locks all do
- Page 351 and 352: 338 Chapter Fifteenwith the Ford an
- Page 353 and 354: 340 Chapter FifteenFigure 15-38. 20
- Page 355 and 356: 342 Chapter FifteenFigure 15-40.Dai
- Page 357 and 358: 344 Chapter FifteenFigure 15-45.PAS
- Page 359 and 360: 346 Chapter FifteenOn any vehicle,
- Page 361: 348 Chapter FifteenFigure 15-50. SR
- Page 365 and 366: 352 Chapter FifteenReview Questions
Body Accessory Systems Operation 349
CAN
BATTERY (+)
AIR BAGS
GROUND (-)
O-RINGS SEALS
SAFING
SENSOR
CRASH
SENSORS
SENSING MASS
ELECTRICAL
CONTACTS
Figure 15-52.
Operations)
Safing sensor. (GM Service and Parts
BIAS MAGNET
FRONT OF CAR
MOUNTING
PLATE
Steering
Wheel
Wiring
Shield
Figure 15-51.
SRS sensors. (DaimlerChrysler Corporation)
only. Although the design of individual systems
varies, the vehicle must be traveling a minimum
of 12–28 mph before the system is armed and
ready for deployment.
All the sensors use some type of inertia switching
mechanism that provides for the breakaway of
a metal ball from its captive magnet. This function
causes a signal to activate a portion of the deployment
program set up in the control processor. The
system is still capable of directly applying battery
power to the squib or detonator. At least two sensors,
one safing sensor and one front crash sensor,
must be activated to inflate the air bag.
Safing Sensors
An integrated version of this network includes a
safing sensor (Figure 15-52), sometimes attached
to the original crash sensor. This device confirms
the attitude and magnitude of the frontal deceleration
forces and offers the microprocessor a second
opinion before actual deployment. This is all
it takes to complete the firing sequence, and the
bag will deploy.
Wiring Harness
The wiring harness connects all system components
into a complete unit. The wires carry the
electricity that signals the air bag to inflate. The
harness also passes the signals during the selfdiagnosis
sequence.
Figure 15-53.
Corporation)
Retainer
Ring
Inflater
Igniter
Mounting
Assembly
Plate
SIR or Air Bag Readiness Light
This light lets the driver know the air bag
system is working and ready to do its job. The
readiness lamp lights briefly when the driver
turns the ignition key from OFF to RUN. A malfunction
in the air bag system causes the light
to stay on continuously or to flash, or the light
might not come on at all. Some systems have
a tone generator that sounds if there is a problem
in the system or if the readiness light is
not functioning.
Air Bag Module
Module
Liner
Bag
Assembly
Air bag module. (DaimlerChrysler
Trim
Cover
Assembly
The bag itself is composed of nylon and is
sometimes coated internally with neoprene. All
the air bag module (Figure 15-53) components
are packaged in a single container, which is
mounted in the center of the steering wheel or
in the dash panel on the passenger side. The
entire assembly must be serviced as one unit
when repair of the air bag system is required.
The air bag module is made up of the following
components.
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