The air bag system used on many vehicles is referred to as the Supplemental Restraint System (SRS). The air bag is designed to deploy when the vehicle is involved in a front end collision of sufficient force, up to 30 degrees off center line of the vehicle.
This system has an energy reserve, which can store a large enough electrical charge to deploy the air bag for 15 seconds (on the Rodeo) or 2 minutes (on the Hombre and Trooper) after the battery has been disconnected or damaged. This system must be disabled if any service is to be performed on the SRS system or steering wheel assembly.
The vehicle may be equipped with a driver side and a passenger side air bag. When a frontal crash occurs of sufficient force, the bag(s) are deployed from both the center of the steering wheel and from above the instrument panel compartment on the passenger's side.
This system has self-diagnostic ability. If any problem is found by the computer the air bag system is disabled and the instrument panel light is turned on. There is no danger of accidental air bag deployment if this light is on, but the air bag system will not work during a collision. The vehicle should be taken to a professional service center if the light remains on.
The air bag system contains a Sensing and Diagnostic Module (SDM), deployment loop and an air bag module. The function of the deployment loop is to supply current through the air bag module in the steering wheel or dash panel, which will cause air bag deployment during a severe accident. The SDM supplies this power, even if the battery has been damaged. The SDM is the heart of the air bag system, it is the computer that performs all the function necessary to deploy the air bag.
Sensing and Diagnostic Module (SDM)
The SDM is designed to perform 7 main functions. It maintains an energy reserve of 24 volts for several seconds, to deploy the air bag in case battery voltage is lost. It monitors the vehicle velocity changes to detect frontal crashes which are severe enough to warrant deployment. It provides the power to the air bag module to deploy the air bag. The SDM performs both malfunction detection and malfunction diagnostic monitoring of the SRS system and records malfunction codes, which can be obtained from a special scan tool. It warns the driver of a malfunction by controlling the Air Bag lamp and keeps a record of the SIR system during a vehicle accident.Air Bag Warning Lamp
The Air Bag Warning lamp is used to verify the SDM operation by flashing 7-9 times when the ignition is first turned ON . It is also used to warn the driver of a SRS malfunction.SRS Coil Assembly
The coil assembly consists of 2 current carrying coils. They are attached to the steering column and allow rotation of the steering wheel, while maintaining continuous contact of the deployment loop through the inflator module.
There is a shorting bar on the lower steering column connector, which connects the SRS coil to the SRS harness. The shorting bar shorts the circuit when the connector is disconnected. The circuit to the module is shorted in this way to help prevent unwanted deployment of the air bag, while performing service.Air Bag Module
DRIVER'S AIR BAG
The air bag module is located in the steering wheel hub under the vinyl trim. It includes the air bag, inflator and initiator. When the vehicle is in an accident, current is passed through the deployment loop. This current passing through the deployment loop ignites the squib in the inflator module. The gas produced rapidly inflates the air bag.
There is a shorting bar on the lower steering column connector, which connects the SRS coil to the SRS harness. The shorting bar shorts the circuit when the connector is disconnected. The circuit to the module is shorted in this way to help prevent unwanted deployment of the air bag, while performing service.PASSENGER AIR BAG
When equipped, the vehicle will have a driver/passenger SRS system with 2 inflator modules. The driver inflator module is located on the steering wheel, while the passenger inflator module is mounted in the instrument panel above the instrument panel compartment. Each module includes the air bag, inflator and initiator. There is a shorting bar on the driver inflator module side of the upper steering column connector. There is also a shorting bar on the passenger inflator module connector, which connects the SRS wiring harness to the passenger inflator module. The shorting bar shorts the passenger inflator module circuit whenever this connector is disconnected. The circuit to the module is shorted in this way to help prevent unwanted deployment of the air bag while performing service.Knee Bolster
The knee bolster is used to absorb energy and control the driver's forward movement during an accident by limiting leg movement. The knee bolster must be in place or sever injury will occurred during an accident.Fuse Panel
The SRS system have a specific fuses in the panel. They are usually identified as SRS1 and SRS2.Wiring Harness and Connectors
The wiring harness and connectors for the SRS system are of special design. Any wiring repairs should be done using tool kit J-38125, or equivalent. Always use the crimp and seal splice sleeves contained in this wiring repair kit. If damage is done to a component pigtail the component must be replaced.
DISARMING THE SYSTEM
Simply disconnecting and isolating the battery cable will disarm the system. If you need to remove the air bag module or work around the air bag you should also disconnect the deployment loop wiring as follows:
- Read all service precautions.
- Turn the wheels straight ahead.
- Turn the ignition switch OFF .
- Disconnect and isolate the negative battery cable.
- Remove the SRS fuses.
- Remove the lower knee bolster.
- Disconnect the yellow 3-way connector from the base of the steering column.
- Disconnect the yellow 2-way connector from behind the glove box.
ARMING THE SYSTEM
If the battery was disconnected, the system will automatically re-arm and perform a self-diagnostics when the battery is connected. Make certain no one is in the vehicle while connecting the battery cables.
If the modules were disconnected perform the following:
- Read all service precautions.
- Turn the ignition switch OFF .
- Connect the yellow 2-way connector from behind the glove box.
- Connect the yellow 3-way connector from the base of the steering column.
- Install the lower knee bolster.
- Replace the SRS fuses.
- Connect the battery cable.