System Operation

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 modules, which will cause deployment of the air bags in the event of a frontal crash of sufficient force, up to 30 degrees OFF the centerline of the vehicle.

The Dual Pole Arming Sensor, SIR Coil Assembly (driver side only), Inflator Modules, Mid-Rail Discriminating Sensors, and Forward Discriminating Sensor make up the Deployment Loops.

The Dual Pole Arming Sensor switches power to the inflator modules on the high side (power side) of the Deployment Loops. Any one of the Discriminating Sensors can supply ground to the inflator modules on the low side (ground side) of the loop. The inflator modules are only supplied sufficient current to deploy when the Dual Pole Arming Sensor and at least one of the three Discriminating Sensors are closed simultaneously.

A function of the Diagnostic Energy Reserve Module (DERM) is to supply the Deployment Loops with a 36 Volt Loop Reserve (36 VLR) to ensure sufficient energy to deploy the air bags if the ignition feed to the Dual Pole Arming Sensor is lost during a frontal crash.

Another function of the DERM is electrical system diagnostics. The DERM monitors the deployment loops in conjunction with the resistors in the Dual Pole Arming Sensor and the Mid-Rail Discriminating Sensors. These resistors make is possible for DERM to detect circuit and component malfunctions within the Deployment Loops. The DERM monitors the voltage drop across each component within the loops during normal, non-deployment operation. If the monitored voltages fall outside of expected limits, the DERM will indicate a malfunction through the storage of a Diagnostic Trouble Code and the illumination of the INFLATABLE RESTRAINT warning lamp.