Seat Occupant Sensor: Description and Operation

OCCUPANT CLASSIFICATION SENSOR

CAUTION:
- It is necessary to rezero the OCS system when a front passenger seat cushion is disassembled, a new trim cover installed, or an OCS service kit is installed. A diagnostic tool is used to trigger the active command to carry out rezeroing of the OCS system.
- Make sure the seat is completely assembled before rezeroing.
- The following precautions must be taken before rezeroing the OCS system:
- Make sure the OCS system components are connected and no faults are present.
- Make sure the OCS system is not at a temperature below 0°C (32°F) or above 45°C (113°F) when initiating the rezeroing process. If the vehicle has been exposed to extreme cold or hot temperatures, the vehicle must be exposed and kept at a temperature within the limits, 0°C to 45°C (32°F to 113°F) for a minimum of 30 minutes.
- Make sure nothing is present on the passenger seat before rezeroing and nothing is placed on the seat during the rezeroing process.
- Make sure a minimum eight second time period has passed after cycling the ignition switch ON before the rezeroing process.

NOTE:
- For best results in rezeroing, the OCS system should be at or near room temperature, 10°C to 29°C (50°F to 85°F).
- When using a New Generation STAR (NGS) Tester you must use the appropriate memory card with the latest update to carry out this function. To rezero the OCS system:
- select "SERVICE BAY FUNCTIONS"
- select "RCM"
- select "SYSTEM RESET"
- select the vehicle from the menu
- view the on-screen information, then press "TRIGGER"

The NGS screen will then display "OCS RESET: REZERO." Press "DONE" (button 8) to rezero the OCS system. The NGS will return to the vehicle menu once rezeroing of the OCS system is complete.

- To rezero the OCS system using the Worldwide Diagnostic System (WDS):
- select the "Toolbox" icon
- select "Body" from the menu
- select "Restraints" from the menu
- select "Seat Weight Sensor ReZero"

After selecting "Seat Weight Sensor ReZero", follow the on-screen prompts to carry out rezeroing of the OCS system.

- The ignition switch must be cycled after rezeroing the OCS system.
- If the first attempt to rezero the OCS system is unsuccessful, a second attempt must be made.

The seat occupant classification sensor (OCS) system is found only on the front passenger seat. The front passenger seat OCS system is comprised of a silicone gel-filled bladder mounted in the seat cushion, a pressure sensor that is mounted to the seat frame and an electronic control unit which is also mounted to the seat frame. Pressure is applied to the OCS system bladder when weight of any occupant or object in the front passenger seat is present. The pressure is then transferred through a tube, is sensed by the OCS system pressure sensor, then electronically communicated to the OCS system electronic control unit (ECU). Based on preprogrammed set points the OCS system ECU will inform the restraints control module (RCM), via a high-speed controller area network (HS-CAN), of the necessary information. The RCM uses this information in determining if the passenger air bag module is to be deployed in the event of a deployable collision. The RCM may also use this information to illuminate/not illuminate the passenger air bag deactivation (PAD) indicator.

When an OCS system fault is present, the air bag indicator lamp will illuminate or the air bag warning chime will be activated (if an air bag indicator fault is present). The SRS then defaults the passenger air bag module to ON (activated) regardless of the size of the occupant in the front outboard passenger seat.

The OCS system components (seat cushion foam pad, bladder with pressure sensor and electronic control unit) are calibrated to each other and are serviced as an assembly. OCS system components are not to be installed separately. If installing a new OCS system, OCS system component or seat cushion foam pad, a new OCS system service kit (seat cushion foam pad, bladder with pressure sensor and electronic control unit) must be installed as an assembly.

The OCS system also interprets a variable voltage signal provided by the safety belt tension sensor to identify the presence of a child safety seat in the front outboard passenger seat. The OCS system then communicates with the restraints control module (RCM), automatically deactivating the passenger air bag module.