Air Bag Systems: Description and Operation

The optional Supplemental Driver Air Bag Restraint System is designed to provide increased accident protection for the driver 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 Driver Air Bag Restraint System consists of two basic subsystems:
- The driver air bag.
- The electrical system; including impact sensors and electronic monitor assembly.

Driver Air Bag
The driver air bag is mounted in the center of the steering wheel. The module consists of:
- Inflator.
- Mounting plate and retainer ring.
- Bag assembly.
- Liner and steering wheel trim cover.

NOTE: The driver air bag module is serviced as a complete assembly.

Inflator
The inflator assembly is not a serviceable item. When the sensors close, signalling a crash, battery power flows to the air bag inflator. Inside the inflator, an igniter converts the electrical signal to thermal (heat) energy, 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 air bag is constructed of neoprene coated nylon, is 673 mm (26.5 inches) in diameter and fills to a volume of about 2.1 cubic feet in approximately 40 milliseconds. It is not a serviceable item.

Mounting Plate and Retainer Ring
The mounting plate and retainer ring attach and seal the bag assembly to the inflator. The mounting bracket is also used to attach the trim cover and to mount the entire module to the wheel. These items are components of the air bag module and cannot be serviced.





Liner and Steering Wheel Trim Cover
The liner is an injection moulded plastic component which encases the air bag assembly and provides support for the steering wheel trim cover assembly. When the air bag is activated, tear seams moulded into the liner and steering wheel trim cover separate to allow inflation of the bag assembly. The liner is a component of the air bag module and is not serviceable.





Diagnostic Monitor
The diagnostic monitor assembly contains a microcomputer that monitors the electrical system components and connections. The monitor performs a self-check of the microcomputer internal circuits and energizes the system readiness indicator lamp during prove out and whenever a fault occurs. System electrical faults can be detected and translated into coded lamp displays. If certain faults occur, the system will be disarmed by a firing disarm device built into the monitor. If a system fault exists and the lamp is malfunctioning, an audible tone will be heard indicating the need for service.

Standard Cluster - Tempo:

Standard Cluster - Topaz, Optional Cluster - Tempo:

System Readiness Indicator Lamp
The system readiness indicator is an instrument cluster-mounted lamp that will momentarily light whenever the ignition switch is turned from OFF to RUN if the air bag system is working properly. If the system is not functioning properly, the lamp will either fail to light, stay on continuously, or light in a flashing mode (if a system fault exists and the lamp is malfunctioning an audible tone will be heard indicating the need for service). If a fault occurs after the prove out the lamp will light either continuously or in a coded flashing mode.

Tone Generator
The air bag readiness lamp is the prime means of determining the air bag system condition. However, a series of five sets of five tones will be heard if the readiness lamp is out and a fault occurs in the system. This also means that the Supplemental Driver Air Bag System is in need of service. The tone pattern will repeat periodically until the fault and lamp outage are serviced. Unless serviced, the Supplemental Driver Air Bag Restraint System may not function properly in the event of an accident.





Steering Column and Wheel
The steering column used with the air bag system is a shortened, fixed column. The adapter has a clockspring assembly to transfer electrical signals from the steering column to the steering wheel for the air bag system. The steering wheel has a stepped, four spoke design to accommodate the air bag module assembly.

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's 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:
- Electronic diagnostic monitor.
- Air bag system readiness indicator lamp.
- Wiring harness.
- Sensors.
- Igniter Assembly.
- Backup power supply.

Sensors





The sensor assembly is an electrical switch which 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.

Five sensors are mounted in the vehicle. Their locations are as follows:
- A dual sensor at the radiator support.
- At the RH fender apron.
- At the LH fender apron.
- At the cowl in the passenger compartment.





At least two sensors, one safing, one front, must be activated to inflate the air bag.

Backup Power Supply
A backup power supply is included in the system to provide air bag deployment in the event the battery or battery cables are damaged in an accident before the sensors can close. The power supply is a capacitor that will leak down in approximately 15 minutes after the battery is disconnected.

WARNING: THE BACKUP POWER SUPPLY SHOULD BE DISCONNECTED BEFORE ANY AIR BAG SYSTEM SERVICE IS PERFORMED.