Module, Occupant Classification (OCM): Operation

The OCS provides electronic message inputs to other electronic modules in the vehicle indicating whether the passenger front seat is occupied and the relative size classification of the seat occupant. The microcontroller within the OCM contains the OCS logic and communication circuitry. The OCM uses On-Board Diagnostics (OBD) and can communicate with other electronic modules in the vehicle as well as with a diagnostic scan tool using the Controller Area Network - Chassis (CAN-C) data bus. This method of communication is also used for OCS diagnosis and testing through the 16-way data link connector located on the driver side lower edge of the instrument panel.

The seat weight sensor and the electronic pressure sensor integral and internal to the OCM allow the OCS logic circuits to sense the relative weight of a load applied to the passenger front seat cushion. When a load is applied to the seat cushion, silicone fluid within the bladder becomes pressurized. These changes in bladder fluid pressure are measured by the electronic pressure sensor circuitry through the OCS pressure hose. As the pressure within the bladder changes, the electronic pressure sensor input to the OCM microcontroller also changes. This electronic pressure sensor input allows the OCM to monitor the passenger front seat cushion by providing a weight-sensing reference to the relative load on the seat cushion.

Pre-programmed decision algorithms and OCS calibration allow the OCM microcontroller to determine the appropriate occupant classification based upon the seat cushion load as signaled by the pressure sensor. The OCM then sends the proper electronic occupant classification status  messages over the CAN-C data bus to the Occupant Restraint Controller (ORC) and the ORC controls the deployment circuits for the passenger front supplemental restraints accordingly.

The OCM continuously monitors all of the OCS electrical circuits and components to determine the system readiness. If the OCM detects a monitored system fault, it sets an active Diagnostic Trouble Code (DTC) and sends the appropriate electronic messages to the ORC over the CAN-C data bus. Then the ORC sets a DTC and sends electronic messages to the Instrument Panel Cluster (IPC) to control airbag indicator operation. The OCM stores the DTC after the fault has been corrected.

The OCM receives battery current on a fused ignition output (RUN/START) circuit through a fuse in the Power Distribution Center (PDC). The OCM circuitry has a path to ground at all times through a ground circuit and take out of the instrument panel wire harness, which it shares with the ORC. This take out is secured to the body sheet metal. These connections allow the OCM to be operational whenever the ignition switch status is ON or START.