Sensor-Seat Weight: Operation

The seat weight sensor units are designed to sense the relative weight of a load applied to the passenger side front seat, which provides a logic input to the microprocessor of the Occupant Classification Module (OCM). When a load is applied to the seat, the strain gauge of each sensor is flexed causing a change of electrical resistance through the strain gauge. These changes in resistance are measured by the sensor and the internal sensor circuitry changes the sensor output voltage.

Each weight sensor receives a nominal five volts and a ground through parallel hard wired circuits from the OCM. The OCM then monitors the output voltage of each sensor on dedicated hard wired data communication circuits. The OCM also monitors the condition of the sensor circuits and will store a Diagnostic Trouble Code (DTC) for any fault that is detected, then send messages to the Occupant Restraint Controller (ORC) to illuminate the airbag indicator in the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN).

The hard wired circuits between the seat weight sensor and the OCM may be diagnosed using conventional diagnostic tools and procedures. Refer to the SYSTEM WIRING DIAGRAMS article. However, conventional diagnostic methods will not prove conclusive in the diagnosis of the seat weight sensors or the electronic controls and communication between other modules and devices that provide features of the Occupant Classification System (OCS). The most reliable, efficient, and accurate means to diagnose the seat weight sensors or the electronic controls and communication related to seat weight sensor operation requires the use of a diagnostic scan tool. Refer to the appropriate ELECTRICAL DIAGNOSTIC article.