See Figure 1
All 1990-1992 models are equipped with an airbag system. The Supplemental Inflatable Restraint (SIR) system helps supplement the protection offered by the seat belts by deploying an air bag from the center of the steering wheel. The air bag deploys when the vehicle is involved in a frontal crash of sufficient force up to 30 degrees off the centerline of the vehicle. To further absorb the crash energy, there is a knee bolster located beneath the instrument panel and the steering column is collapsible.
The main portions of the SIR system are the deployment loops and the Diagnostic Energy Reserve Module (DERM). The main function of the deployment loops is to supply current through the inflator module(s), which will cause deployment of the air bag(s) in the event of a frontal crash of sufficient force. The arming sensor, SIR coil assembly (driver side only), passenger inflator module jumper (passenger side only), inflator module(s), passenger compartment discriminating sensor and forward discriminating sensor make up the deployment loops.
The DERM has two functions. One to supply the deployment loops with a 36 volt reserve to ensure sufficient energy is available to deploy the airbag(s) if the battery voltage feed to the arming sensor is lost during a frontal crash. Another function is SIR electrical system diagnostics.
The arming sensor switches power to the inflator module(s) on the high side (power side) of the deployment loops. Either of the discriminating sensors can supply ground to the inflator module(s) on the low side (ground side) of the loop. The inflator module(s) are only supplied sufficient current to deploy when the arming sensor and at least one of the two discriminating sensors are closed simultaneously.
See Figures 2 and 3Diagnostic Energy Reserve Module
The DERM is designed to perform the following functions in the SIR system:
The "INFL REST" or "AIR BAG" warning lamp is used to do the following:
The arming sensor is a protective switch located in the power feed side of the deployment loop. It is calibrated to close at low level velocity changes (lower than the discriminating sensors). This assures that the inflator module is connected directly to the 36 volt output of the DERM or battery voltage feed when either of the discriminating sensors close.Discriminating Sensors
The discriminating sensors are wired in parallel on the ground side of the deployment loop. These sensors are calibrated to close with velocity changes which are severe enough to warrant deployment.SIR Coil Assembly
The SIR coil assembly consists of two 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 to the inflator module.Inflator Modules
Each inflator module consists of an inflatable bag and an inflator (a canister of gas generating material with an initiating device). When the vehicle is in a frontal crash of sufficient force, current flows through the deployment loops. Current flowing through the initiator ignites the material in the inflator module. The gas produced from this reaction rapidly inflates the air bag.
See Figures 4 and 5
The DERM can maintain sufficient voltage to cause a deployment for up to 10 minutes after the ignition switch is turned OFF or the battery is disconnected. Always disable the system when performing service procedures ON OR NEAR the system and it's components.
DISARMING THE SYSTEM
- Turn the steering wheel so that the vehicle's wheels are pointing straight ahead.
- Turn the ignition switch to the LOCK position.
- Remove the SIR or AIR BAG fuse from the fuse panel.
- Remove the left side trim panel, then remove the Connector Position Assurance (CPA) device and disconnect the yellow two-way SIR harness connector at the base of the steering column.
- On vehicles with passenger side air bags, remove the glove box door then disconnect the yellow two-way connector located near the yellow 24-way DERM harness connector.
With the fuse removed and the ignition switch ON, the air bag warning lamp will be on. This is normal and does not indicate a SIR system malfunction.
ARMING THE SYSTEM
- Turn the ignition key to the LOCK position and remove the key.
- On vehicles with a passenger side air bag, reconnect the yellow two-way connector assembly located near the yellow 24-way DERM harness connector. Install the glove box door assembly.
- Connect the yellow two-way connector assembly at the base of the steering column.
Always be sure to reinstall the Connector Position Assurance (CPA) device.
- Install the left side trim panel and reinstall the fuse in the fuse block.
- Turn the ignition key to the RUN position and verify that the warning lamp flashes seven to nine times and then turns OFF. If it does not operate as described, have the system repaired by a qualified technician.