Module, Occupant Classification: Operation: Operation
The Occupant Classification System (OCS) provides electronic message inputs to other electronic modules in the vehicle indicating whether the passenger seat is occupied and the relative size classification of the seat occupant. The microcontroller in the Occupant Classification Module (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 (CAN) 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 (SWS) (also known as the seat weight bladder) 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 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 seat cushion by providing a weight-sensing reference to the relative load on the seat cushion.
A Belt Tension Sensor (BTS) also receives a nominal five volts and a ground through dedicated hard wired circuits from the OCM. The OCM then monitors the belt tension sensor output voltage on a dedicated hard wired data communication circuit. The belt tension sensor unit is designed to sense the relative cinch load applied to the passenger seat belt, which provides an additional logic input to the microcontroller of the OCM. When a load is applied to the seat belt, the changes in the load are measured by the belt tension sensor through the seat belt lower anchor. As the load changes, the circuitry of the belt tension sensor changes the output voltage of the sensor.
Pre-programmed decision algorithms and OCS calibration allow the OCM microcontroller to determine the appropriate occupant classification based upon the passenger seat cushion load as signaled by the pressure sensor and passenger seat belt cinch load as signaled by the BTS. The OCS is programmed to differentiate seat occupant classification as empty, occupied by a child seat or an individual below a minimum weight threshold, or occupied by an individual above a minimum weight threshold. The minimum weight threshold is defined as either less than or more than the weight of a fifth percentile female. The OCM then sends the proper electronic occupant classification status messages over the CAN data bus to the Occupant Restraint Controller (ORC).
The ORC controls the deployment circuits for the passenger supplemental restraints based upon inputs from the OCM and, based upon that input as well as hard wired inputs from the seat belt switches, sends electronic messages to the Instrument Cluster (IC) (also known as the Common Instrument Cluster/CIC) to control Passenger AirBag (PAB) on/off indicator (also known as the Passenger Airbag Disable Lamp/PADL) and the seat belt reminder indicator accordingly. The ORC is programmed to suppress PAB deployment and turn the PAB on/off indicator Off if the passenger seat is empty, suppress PAB deployment and turn the PAB on/off indicator On if the passenger seat is occupied by a child seat or someone below the minimum weight threshold, or enable PAB deployment and turn the PAB on/off indicator Off if the passenger seat is occupied by someone above the minimum weight threshold.
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 and stored Diagnostic Trouble Code (DTC) and sends the appropriate electronic messages to the Occupant Restraint Controller (ORC) over the CAN data bus. Then the ORC sets a DTC and sends electronic messages to the IC to control airbag indicator operation.
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 metal body structure. These connections allow the OCM to be operational whenever the ignition switch (also known as the Keyless Ignition Node/KIN or IGnition Node Module/IGNM) status is On or Start.
The hard wired inputs and outputs for the OCM may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information. However, conventional diagnostic methods will not prove conclusive in the diagnosis of the OCM or the electronic controls and communication between other modules and devices that provide some features of the OCS. The most reliable, efficient and accurate means to diagnose the OCM or the electronic controls and communication related to OCS operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.