Discriminating Sensors

SIR system uses 2 or more discriminating sensors. Some models have 2 forward discriminating sensors; others have one forward discriminating sensor and one passenger compartment sensor. Some models have one forward discriminating sensor and a left or right (engine compartment) discriminating sensor.

The forward discriminating sensor(s) is located on the radiator support brace. The passenger compartment discriminating sensor is located under the center of the instrument panel/console area or under the front passenger seat. The left/right discriminating sensor is located on the left or right frame rail, next to shock tower. In some models, the passenger compartment discriminating sensor is combined with the arming sensor and is known as a dual sensor.

Discriminating sensors are wired in parallel on the ground side of the deployment loop. These sensors are calibrated to close when deceleration velocity changes are severe enough to warrant deployment.

The sensors consist of a sensing element, normally open switch contacts and a diagnostic resistor. The sensing element closes the normally open switch contacts when the vehicle velocity changes are severe enough to warrant deployment.

A diagnostic resistor is connected parallel with the normally open switch contacts within each of the sensors. These parallel resistors supply the ground path for the current passing through the deployment loop during normal non-deployment conditions. This small current flow results in a voltage drop across each component within the loop. The DERM monitors these voltage drops to detect circuit or component faults.