Occupant Classification System
In early production vehicles equipped with the Occupant Classification System (OCS), the OCS automatically suppresses or enables passenger airbag and seat belt tensioner operation based upon whether or not the passenger side front seat is occupied and, if the seat is occupied, classifies the size of the occupant or whether the seat is occupied by a child seat. In late production vehicles without the passenger airbag on/off indictor, the passenger airbag and seat belt tensioner are always enabled, but the airbag is deployed much less forcefully when the system senses the seat is occupied by a child seat or a person below a minimum weight threshold.
The OCS has an Occupant Classification Module (OCM) that monitors inputs from the seat weight sensors under the passenger side front seat cushion and from the seat track position sensors on the passenger side and driver side seat adjuster tracks. Based upon those inputs the microprocessor within the OCM classifies the occupant of the passenger side front seat, and the proximity of each front seat to the front airbags. The OCM then sends electronic occupant classification messages to the Occupant Restraint Controller (ORC). On early production vehicles, the microprocessor and programming of the ORC determines whether to enable or disable the deployment circuits for the passenger airbag and seat belt tensioner; and, if enabled, what force level should be used to deploy each front airbag. On late production vehicles the passenger airbag deployment circuits are always enabled with the ignition switch in the ON position, so the ORC microprocessor and programming determine only the force level appropriate for the airbag deployment.
The OCS electrical circuits and components are continuously monitored by the OCM, and the OCM is continuously monitored by the ORC. Early production vehicles have a passenger airbag on/off indicator located in the upper switch pod near the top of the instrument panel lower center bezel. This indicator receives battery current whenever the ignition switch is in the ON or START positions, and illuminates only when the ORC pulls the indicator control circuit to ground. The indicator illuminates for about seven seconds as a bulb test each time the ignition switch is turned to the ON or START positions. Following the bulb test, the indicator is turned ON or OFF by the ORC based upon the electronic occupant classification messages received from the OCM. This indicator is illuminated whenever the seat is occupied and passenger airbag and seat belt tensioner operation has been suppressed. The indicator is turned OFF whenever the seat is empty or when the seat is occupied and the passenger airbag and seat belt tensioner are enabled.
When the OCM monitors a problem in any of the OCS circuits or components, it stores a fault code or DTC in its memory circuit and sends an electronic message to the ORC. The ORC then sends an electronic message to the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN) to turn ON the airbag indicator. If for any reason the OCM is unable to classify the occupant it sends an electronic message to the ORC, and the ORC suppresses passenger airbag and seat belt tensioner operation. The hard wired circuits between components related to the OCS may be diagnosed using conventional diagnostic tools and procedures. Refer to the SYSTEM WIRING DIAGRAMS article. The wiring information includes wiring diagrams, proper wire and connector repair procedures, details of wire harness routing and retention, connector pin-out information and location views for the various wire harness connectors, splices and grounds.
However, conventional diagnostic methods will not prove conclusive in the diagnosis of the OCS or the electronic controls or communication between other modules and devices that provide features of the OCS. The most reliable, efficient, and accurate means to diagnose the OCS or the electronic controls or communication related to OCS operation, as well as the retrieval or erasure of a DTC requires the use of a diagnostic scan tool. Refer to the appropriate ELECTRICAL DIAGNOSTIC article.
See the owner's manual in the vehicle glove box for more information on the features, use and operation of the OCS.