Inflatable Restraint Electronic Frontal Sensor (EFS)
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2004 Oldsmobile Bravada, 2004 GMC Envoy XUV, 2004 GMC Envoy XL, 2004 GMC Envoy, and 2004 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
The electronic frontal sensor (EFS) (also known as inflatable restraint front end discriminating sensor) is equipped on some vehicles to supplement the SIR system performance. The EFS is an electronic sensor (accelerometer) and is not part of the deployment loops, but instead provides an input to the SDM. The EFS can assist in determining the severity of some frontal collisions. The SDM contains a microprocessor which performs calculations using the measured accelerations and compares these calculations to a value stored in memory. When the generated calculations exceed the stored value, the SDM will cause current to flow through the frontal deployment loops deploying the frontal air bags.