Sensor Module

WARNING: This page is about a different car, the 1996 Volvo 850. However, it is still accessible from the selected car via links, so may be relevant.

Sensor measures and records deceleration/collision force of vehicle to determine if air bag deployment is necessary. Sensor module also functions as a diagnostic monitor, which continuously monitors SRS operation and records any faults in SRS. Sensor incorporates a piezoelectric sensor (to detect deceleration/collision force), microprocessors (to evaluate collision signal and control SRS deployment), a memory (to retain information for fault tracing if power supply fails) and a standby power unit (if battery power supply is lost).

Electrical sensor records combination of "G" force and change in speed (deceleration). Both high "G" force and prolonged deceleration are required to activate SRS. Consequently, sensor module cannot be activated by a hammer blow or other similar influence, which produces a high "G" force for a short time.

To ensure correct operation of sensor module, it must be properly secured to floor and securely grounded. Sensor module is grounded by a short Black wire connected to one of sensor module mounting screws. SRS is monitored continuously by microprocessors in sensor module, regardless of ignition switch position or engine operation. Sensor module will illuminate instrument gauge cluster SRS warning light until a fault is corrected, and sensor module memory is cleared.

Sensor module incorporates a standby power unit if normal power source (battery voltage) is interrupted. Standby power unit stores enough energy to deploy SRS within 100 milliseconds of battery power loss during a collision.