The three impact sensors used in the SRS system verify the direction and severity of an impact. One of the sensors is called the safing sensor. It is located in the Air Bag Control Module (ACM), which is mounted to a bracket under the instrument panel, on top of the floor pan transmission tunnel. The other two are impact sensors and are mounted on the left and right inner fender extension panels behind the grille. The sensors are calibrated for the particular vehicle that they serve.
The impact sensors are threshold-sensitive switches that complete an electrical circuit when an impact provides a sufficient deceleration force to close the switch. The safing sensor is an accelerometer that senses the rate of deceleration. The microprocessor in the ACM monitors the sensor signals. A pre-programmed decision algorithm in the microprocessor determines when the deceleration rate indicates an impact that is severe enough to require air bag system protection.
The two impact sensors are available for service replacement. The safing sensor is only serviced as part of the ACM.