Seat Occupant Sensor: Description and Operation
Occupant Detection Sensor
Description
An Occupant Detection Sensor (ODS) is located below the passenger side front seat cushion trim cover. This sensor provides information to the Occupant Restraint Controller (ORC) used for control of the passenger belt alert feature.
The ODS consists of a flexible clear plastic mat (1) containing several resistive membrane, force sensing resistor cells. In vehicles with a molded in place seat trim cover, the sensor is actually enclosed within a heat staked film envelope or pocket that is then molded into the seat cushion foam. In vehicles with a cut and sewn seat trim cover, the sensor is secured by two adhesive patches (2) to the seat cushion foam. In cut and sewn seats with an optional seat heater, the heater mat is secured with adhesive over the top of the seat cushion foam with the sensor sandwiched between the heater mat and the cushion foam.
A short, two-conductor pigtail wire and connector (4) connect the sensor to the vehicle electrical system through a dedicated take out and connector of the seat wire harness. A hot melt adhesive block (3) encapsulates and protects the connections between the electrical conductors in the tail of the sensor mat and the pigtail wires as well as a diagnostic resistor.
The ODS cannot be adjusted or repaired, and must be replaced if damaged or ineffective. In seats with a molded in place trim cover, the ODS can only be serviced by replacing the entire seat cushion foam and trim assembly. In seats with a cut and sewn trim cover and a heater mat, the ODS can only be serviced by replacing the entire seat cushion foam, ODS and heater mat unit. In seats with a cut and sewn trim cover and no heater mat, the ODS is available for individual service replacement.
Operation
The Occupant Detection Sensor (ODS) acts as a simple switch to detect loads placed upon the passenger side front seat cushion. The sensor circuits are connected to and monitored by the Occupant Restraint Controller (ORC) whenever the ignition switch is in the ON position. The ORC uses an algorithm logic in monitoring the changing states of the sensor input to determine whether the seat cushion load is static or dynamic.
The ORC microprocessor continuously monitors all of the Supplemental Restraint System (SRS) electrical circuits to determine the system status and readiness. If the ORC detects a monitored system fault, it sets a Diagnostic Trouble Code (DTC). However, because the ODS input is only used for control of the passenger belt alert feature, which has no effect on SRS component features or functions, the airbag indicator is NOT illuminated in response to a detected ODS circuit fault.
The ODS receives source current and a clean ground through dedicated sensor plus and minus circuits from the ORC. The ORC then sends the appropriate sensor status information to the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN), which uses this information as an additional logic input for control of the seat belt indicator and the passenger belt alert feature.
The hard wired circuits between the ODS and the ORC 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 ODS or the electronic controls and communication between other modules and devices that provide some features of the passenger belt alert feature. The most reliable, efficient, and accurate means to diagnose the ODS or the electronic controls and communication related to passenger belt alert feature operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.