Supplemental Restraint System (SRS)
The Supplemental Air Bag Restraint System is designed to provide increased accident protection for front seat occupants IN ADDITION TO that provided by the 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 restraint system. FORD RECOMMENDS THE USE OF SAFETY BELT SYSTEMS FOR ALL VEHICLE OCCUPANTS.
The Supplemental Air Bag Restraint System (SRS) consists of:
- Electrical system
- Driver side air bag module
- Sensors:
^ Primary air bag sensors
^ Safing air bag sensor
- Air bag diagnostic monitor
- Air bag indicator
- Tone generator
AIR BAG SYSTEM FUNCTIONS
The following four steps show how the supplemental air bag restraint system functions.
NOTE: Steps 1-3 take place in a fraction of a second.
1. The sensors in the vehicle detect a severe frontal impact. When a center air bag primary crash sensor or front air bag (RH) primary crash sensor and the RH cowl side panel front air bag safing sensor are closed at the same time, electric current flows to the inflator and ignites the chemicals.
2. The chemicals then rapidly burn in the metal container. The rapid burning produces nitrogen gas and small amounts of dust. The nitrogen gas and dust are cooled and filtered during inflation of the air bag.
3. The inflating air bag splits open the trim cover. The air bag then rapidly unfolds and inflates in front of the driver.
4. After inflation, the gas empties through holes in the air bag. The air bag deflates very rapidly.
ELECTRICAL SYSTEM
The supplemental air bag restraint system is powered directly from the battery. The supplemental air bag restraint system can function with the ignition switch in any position, including OFF and LOCK. The supplemental air bag restraint system can also function when the front seat is unoccupied. The electrical system performs three main functions:
- Detects impacts
- Supplies electric power to the igniter(s)
- Monitors the system to determine system readiness
The electrical system components include:
- Air bag diagnostic monitor
- Air bag indicator
- Wiring harness and air bag sliding contact
- Sensors:
^ Primary air bag sensor and bracket (crash sensors)
^ Safing air bag sensor
- The igniter within the driver side air bag module
SENSORS
WARNING: VEHICLE SENSOR ORIENTATION IS CRITICAL FOR PROPER SYSTEM OPERATION. IF A VEHICLE EQUIPPED WITH A SUPPLEMENTAL AIR BAG RESTRAINT SYSTEM HAS BEEN INVOLVED IN A CRASH WHERE THE RADIATOR SUPPORT, FRAME RAILS OR COWLS HAVE BEEN DAMAGED, INSPECT THE SENSOR MOUNTING BRACKETS FOR DEFORMATION. IF DAMAGED, THE SENSOR SHOULD BE REPLACED WHETHER OR NOT THE AIR BAG IS DEPLOYED. IN ADDITION, MAKE SURE THE BODY STRUCTURE IN THE AREA OF THE SENSOR MOUNTING IS RESTORED TO ITS ORIGINAL CONDITION.
NOTE: Undamaged sensors will reset automatically after an accident and can be reused.
The sensors are electrical switches which react to impacts according to direction and force. Sensors discriminate 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.
Three sensors are mounted in the vehicle. Their locations are as follows:
- A primary air bag sensor at the center of the radiator support.
- A primary sensor on the right frame rail.
- A safing sensor at the right cowl side trim panel.
At least two sensors (one primary sensor and one safing sensor) must be closed to inflate the air bag.
The sensors automatically "reset" after a collision and do not need to be replaced unless they are physically damaged. Replace only if proper alignment is not possible due to bent brackets, cut wires, smashed connectors, etc.
AIR BAG SYSTEM COMPONENT LOCATION
1. Center air bag primary crash sensor - center of radiator support.
2. Right frame rail primary crash sensor - right frame rail at B-pillar support.
3. Right cowl side panel safing sensor - right cowl side trim panel.
4. Driver side air bag module - steering wheel.
5. Air bag sliding contact - behind steering wheel.
6. Air bag diagnostic monitor-under instrument panel left of steering column.
NOTE:
- A thermal fuse is built into the air bag diagnostic monitor. If a short to ground should occur in the air bag deployment circuit, the microcomputer in the air bag diagnostic monitor will send a signal to the fuse causing it to open. The open fuse removes all firing power (battery/backup power) from the deployment circuits. This prevents unwanted air bag deployments due to damaged vehicle wiring.
- Code 51 is displayed whenever the diagnostic monitor thermal fuse is open and no other higher priority faults exist (consult Diagnostic Trouble Code Priority Table). Code 51 is normally seen after service of a Code 13 condition.
- If a Code 51 exists and a Code 13 condition has not been serviced, this means an intermittent short-to-ground exists in the air bag deployment wiring. The intermittent short-to-ground must be located and serviced before servicing the Code 51 condition.
- Since the thermal fuse is built into the air bag diagnostic monitor, the monitor must be replaced to service a Code 51 condition. NEVER replace the air bag diagnostic monitor without first determining the cause for the Code 51 condition. If the short-to-ground is not properly serviced, the short may reoccur, once again destroying the thermal fuse in the air bag diagnostic monitor.