Principles of Operation: Notes

WARNING: This page is about a different car, the 2007 Lincoln MKX and 2007 Ford Edge. However, it is still accessible from the selected car via links, so may be relevant.

The supplemental restraint system (SRS) consists of a driver and passenger air bag module, safety belt pretensioners and safety canopies (containing an inflator/squib or gas generator and an air bag), impact sensors, a restraints control module (RCM), a clockspring, an air bag warning indicator lamp, occupant classification sensor (OCS) system and a passenger air bag deactivation (PAD) indicator lamp. These components are all interconnected by a wiring harness and powered by the vehicle's battery. The RCM includes a backup power supply. This feature provides sufficient backup power to deploy the SRS in the event that the ignition circuit is lost or damaged during impact. The backup power supply will deplete its stored energy approximately one minute after the battery ground cable is disconnected. If a SRS fault exists, the air bag warning indicator will illuminate and remain illuminated for the rest of the key cycle. In addition to the self-test at start up, the RCM continuously monitors all of its external and internal circuitry for faults.

In a frontal collision, the impact sensors located in the front of the vehicle detect the sudden deceleration and send an electrical signal to the RCM. The RCM uses the information from the impact sensors and the occupant classification system module (OCSM) in the deployment determination. If the RCM determines that deployment is required, the RCM sends voltage and current to the squib(s) causing the solid chemical propellant to undergo a rapid chemical reaction. This controlled reaction produces harmless nitrogen gas that fills the air bag(s)/safety canopies and/or activates the safety belt pretensioners to remove slack from the safety belt(s).

The RCM communicates through the data link connector (DLC) the current and historical diagnostic trouble codes (DTCs) on the high-speed controller area network (HS-CAN). The RCM also communicates over the HS-CAN to the instrument cluster module, powertrain control module (PCM) and the OCSM.