Air Bag Systems: Description and Operation
The supplemental air bag restraint system is designed to provide increased collision protection for the front seat occupants in addition to that provided by the driver three-point safety belt system.
- Safety belt use is necessary to obtain the best occupant protection and to receive the full advantages of the supplemental air bag.
- Ford recommends the use of safety belt systems for all vehicle occupants.
The supplemental air bag restraint system consists of two basic sub-systems:
- Driver side air bag module and passenger side air bag module.
- Electrical system including center cowl primary crash front air bag sensor and bracket, center radiator primary crash front air bag sensor and bracket, LH kick panel safing rear air bag sensor and bracket, and air bag diagnostic monitor.
DRIVER SIDE AIR BAG MODULE
CAUTION: The driver side air bag module is serviced as a complete assembly.
The driver side air bag module is mounted in the center of the steering wheel. The driver side air bag module consists of the following components:
- Inflator.
- Mounting plate and retainer ring.
- Airbag.
- Steering wheel trim cover.
Inflator
NOTE: The inflator assembly is not a serviceable item.
- When the sensors close, signaling a crash, electrical current flows to the air bag inflator.
- Inside the inflator, an igniter converts the electrical signal to thermal energy (heat), causing the ignition of the inflator gas generant.
- This ignition reaction combusts the sodium azide/copper oxide gas generant in the inflator, producing nitrogen gas, which inflates the air bag.
Air Bag
The driver side air bag:
- Is constructed of neoprene-coated nylon.
- Is 711 mm (28 inches) in diameter.
- Fills to about 0.065 cubic meter (2.3 cubic feet) in approximately 40 milliseconds.
- Is not a serviceable item.
Mounting Plate and Retainer Ring
The mounting plate and retainer ring:
- Attach and seal air bag assembly to the inflater.
- Also attach the trim cover and mount the entire driver side air bag module to the steering wheel.
- Are components of the driver side air bag module and cannot be serviced.
Steering Wheel Trim Cover
The steering wheel trim cover:
- Encases the driver side air bag module.
- Has moulded in tear seams that separate to allow inflation of the bag.
- Is a component of the driver side air bag module and is not serviceable.
PASSENGER SIDE AIR BAG MODULE
NOTE: The passenger side air bag module is serviced as a complete assembly. Perform proper disposal procedure.
The passenger side air bag module is mounted in the RH position of the instrument panel above the glove compartment. The passenger side air bag module consists of the following components:
- Inflator.
- Airbag.
- Reaction housing with mounting hardware.
- Trim cover.
Inflator
The passenger air bag inflator operates as follows:
- An igniter inside the inflator converts the electrical energy to thermal energy (heat) causing the gas generant to ignite, as with the driver air bag inflator.
- The ignition reaction combusts the sodium azide/copper oxide gas generant to produce nitrogen which fills the air bag.
- Since the passenger side air bag module is much larger than the driver side air bag module, it contains more gas generant in a different inflator configuration to produce more nitrogen gas.
- It is a component of the passenger side air bag module and is not serviceable.
Air Bag
The passenger side air bag:
- Is constructed of ripstop nylon.
- Fills to a volume of about 0.227 cubic meter (8 cubic feet).
- It is not a serviceable item.
Reaction Housing
The steel reaction housing:
- Supplies support for the inflator.
- Provides a reaction surface for the passenger side air bag module.
- Is used to attach the trim cover.
- Contains mounting brackets that attach the passenger side air bag module to the instrument panel.
- Is not a serviceable item.
Trim Cover
The thermo-plastic trim cover:
- Is textured and painted to match the surface of the instrument panel.
- Is constructed with a moulded-in tear seam that separates when the air bag inflates and hinges out of the way during deployment.
- Retains the air bag in the reaction housing during vehicle operation.
- Is not a serviceable item.
Air Bag Diagnostic Monitor
WARNING: THE BACK-UP POWER SUPPLY ENERGY MUST BE DEPLETED BEFORE ANY AIR BAG COMPONENT SERVICE IS PERFORMED. TO DEPLETE BACK-UP POWER SUPPLY ENERGY, DISCONNECT THE NEGATIVE BATTERY CABLE AND WAIT ONE MINUTE TO AVOID ACCIDENTAL DEPLOYMENT AND POSSIBLE PERSONAL INJURY.
The air bag diagnostic monitor:
- Continually monitors all air bag system components and wiring connections for possible faults in the system.
- Will display a Diagnostic Trouble Code on the air bag warning indicator if it detects a fault in the air bag system when the ignition switch is in RUN.
- Performs system diagnostics which is its main function.
- The air bag diagnostic monitor does not deploy the air bags in the event of a crash.
- The crash sensors are "hard wired" to the air bags, and therefore determine when to deploy the air bags.
Several important features of the air bag diagnostic monitor and its functions within the system are described below. It is necessary that you understand these key features and functions. They will enable you to better understand and perform more efficient air bag system diagnostics.
Air Bag System Functions
- The air bag diagnostic monitor illuminates the air bag warning indicator for approximately six seconds when the ignition switch is turned to RUN and then turns it OFF. This indicates that the air bag warning indicator is operational. If the air bag warning indicator does not illuminate or if the air bag warning indicator stays ON or flashes at any time, a fault has been detected by the air bag diagnostic monitor.
- Diagnostic trouble codes may not be displayed for approximately 45 seconds after the ignition switch has been switched to RUN. This is the amount of time it takes the air bag diagnostic monitor to perform all tests and verify system faults, if present.
- Diagnostic trouble codes are displayed as a series of flashes and pauses of the air bag warning indicator. Each diagnostic trouble code, or series of flashes, represents a two-digit number. For example, a Diagnostic Trouble Code 32 is displayed as follows:
Flash flash flash - (one-second pause) - flash flash - (three-second pause)...
Flash flash flash - (one-second pause) - flash flash - (three-second pause)...
- If a system fault exists and the Air Bag Warning Indicator is malfunctioning, an audible tone will be heard indicating the need for service. The tone is a series of five sets of five beeps. This does not indicate a diagnostic trouble code 5. It means that the air bag warning indicator is out and a system fault exists that requires service.
- If a fault exists that makes unwanted air bag deployment possible, the air bag diagnostic monitor has an internal thermal fuse that will blow automatically. This removes all power to the air bag deployment circuit. The air bag warning indicator will flash the appropriate code to indicate the suspect circuit.
The thermal fuse is controlled by a microprocessor inside the air bag diagnostic monitor and is not serviceable.
NOTE: The thermal fuse does not blow because of excessive current flowing through it. Do not attempt to short circuit the thermal fuse with a circuit breaker of any other type of fuse.
- Diagnostic trouble codes are prioritized numerically so that if two or more different faults occur at the same time, the fault having the highest priority will be displayed first. The highest priority fault will be displayed until it is corrected. After it has been corrected, the next highest priority fault will be displayed.
WARNING: TO AVOID PERSONAL INJURY, THE BACK-UP POWER SUPPLY ENERGY MUST BE DEPLETED BEFORE ANY AIR BAG COMPONENT SERVICE IS PERFORMED. TO DEPLETE BACK-UP POWER SUPPLY ENERGY, DISCONNECT THE NEGATIVE BATTERY CABLE AND WAIT ONE MINUTE.
- The air bag diagnostic monitor includes an internal back-up power supply. This feature provides sufficient back-up power to deploy the air bags in the event that the battery or battery cables are damaged in a collision before the crash sensors close. The back-up power supply will deplete its stored energy approximately one minute after the negative battery cable is disconnected.
Steering Column, Wheel, and Air Bag Sliding Contact
The steering column has an air bag sliding contact to carry electrical signals from the steering column through the steering wheel and to the driver side air bag module, horn and speed control.
The steering wheel has a stepped, four-spoke design to accommodate the driver side air bag module.
Electrical System
The air bag system is powered directly from the battery. The system can function with the ignition switch in any position, including OFF and LOCK. The system can also function when the driver or passenger seat is unoccupied. The electrical system performs three main functions:
- Detects an impact.
- Switches electric power to the igniter.
- Monitors the system to determine readiness.
The electrical system components include:
- Air bag diagnostic monitor with integrated back-up power supply.
- Air bag system warning indicator.
- Wiring harness and air bag sliding contact.
- Center cowl primary crash front air bag sensor and bracket, center radiator primary crash front air bag sensor and bracket, LH kick panel safing rear air bag sensor and bracket.
- Igniter within the driver side air bag module and passenger side air bag module.
Sensors
The sensor is an electrical switch which operates as follows:
- It reacts to impacts according to direction and force.
- It discriminates between impacts that require air bag inflation and impacts that do not require air bag inflation.
- When an impact occurs that requires air bag inflation, the sensor contacts close, completing the electrical circuit necessary for system operation.
The sensors in the vehicle determine if air bag inflation is required in the following manner:
1. During severe frontal deceleration caused by an impact that decelerates the vehicle in the forward direction, both a primary crash sensor and a safing sensor will activate.
2. When a primary and safing sensor are closed at the same time, electrical current will flow, igniting the air bag(s).
The primary sensors measure the crash severity, while the safing sensor confirms the crash. The safing sensor is used to prevent inadvertent deployments possibly caused by a malfunction in the primary crash sensor circuits or crash sensors.
Three sensors are mounted in the vehicle. Their locations are:
- A center cowl primary crash front air bag sensor and bracket at the center cowl top in engine compartment.
- A center radiator primary crash front air bag sensor and bracket at the center front radiator support.
- A safing rear air bag sensor and bracket at the LH kick panel in the passenger compartment.
The air bag system is designed to:
- Operate in frontal or front-angled collisions.
- Activate in a crash with severe frontal deceleration, more severe than hitting a parked car of similar size and weight head-on at about 45 km/h (28 mph).
- Sense the severity of the crash rather than vehicle speed so some frontal collisions at speeds above 45 km/h (28 mph) may not be severe enough to require air bag inflation.