OCCUPANT CLASSIFICATION MODULE
DESCRIPTION
The Occupant Classification Module (OCM) (1) is secured with one screw and one tab to the passenger side front seat cushion pan under the front edge of the seat cushion. Concealed within a hollow in the center of the molded plastic OCM housing is a microprocessor and the other electronic circuitry of the module. The module housing is sealed to enclose and protect the internal electronic circuitry.
Four mounting tabs (2) and two connector receptacles (3) are integral to the OCM housing. One mounting tab is inserted into a slot in a dimpled pocket formation of the seat cushion pan, while a screw secures another tab to the seat pan. The remaining two mounting tabs are unused in this application. The connector receptacles contain terminal pins that connect the OCM to the vehicle electrical system through dedicated take outs and connectors of the passenger side front seat wire harness.
The OCM and all of the other components of the Occupant Classification System (OCS) including the passenger side front seat, the seat weight sensors, and the seat adjusters, cushion, back, frame, foam, springs, and wiring harness are a factory-calibrated and assembled unit. Any time any one of these components is removed or replaced for any reason, the OCM must be re-calibrated using a diagnostic scan tool, the Occupant Classification Seat Weight special tool, and the Occupant Classification System Verification Test. Refer to the appropriate diagnostic procedures.
The OCM cannot be adjusted or repaired and, if damaged or ineffective, it must be replaced. The OCM software is flash programmable. A non-calibrated OCM is available for separate service replacement.
OPERATION
The microprocessor in the Occupant Classification Module (OCM) contains the Occupant Classification System (OCS) logic circuits. The OCM uses On-Board Diagnostics (OBD) and can communicate with other electronic modules in the vehicle as well as with the 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 OCM provides voltage to the four seat weight sensors located on the corners of the passenger side front seat, and to the seat track position sensors on the outboard passenger and driver side front seat upper seat tracks. The OCM then monitors return inputs from each of the sensors on dedicated hard wired data communication circuits. The seat weight sensor inputs allow the OCM to determine whether the passenger side front seat is occupied and the relative size of the occupant by providing a weight-sensing reference to the load on the seat. The seat track position sensors provide additional logic inputs to the OCM microprocessor that allow it to determine the position of the front seat passenger and the driver relative to the front airbags.
Pre-programmed decision algorithms and OCS calibration allow the OCM microprocessor to determine when passenger airbag protection is appropriate based upon the seat load as signaled by the seat weight sensors. When the programmed conditions are met, the OCM sends the proper electronic occupant classification messages over the CAN data bus to the Occupant Restraint Controller (ORC), and the ORC controls the deployment circuits for the passenger front supplemental restraints. On vehicles so equipped, the ORC also provides a control output for the passenger airbag on/off indicator in the instrument panel based upon the electronic occupant classification messages it receives from the OCM.
The OCM also sends electronic driver and passenger seat track position messages to the ORC over the CAN data bus. The ORC uses the seat track position data as an additional logic input for determining the force level with which to deploy the multistage front airbags.
The OCM microprocessor 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 ORC over the CAN data bus. Then the ORC sets a DTC and sends messages to control the airbag indicator operation accordingly. An active fault only remains for the duration of the fault, or in some cases for the duration of the current ignition switch cycle, while a stored fault causes a DTC to be stored in memory by the OCM and the ORC. For some DTCs, if a fault does not recur for a number of ignition cycles, the OCM will automatically erase the stored DTC. For other internal faults, the stored DTC is latched forever.
The OCM receives battery current on a fused B(+) circuit through a fuse in the Totally Integrated Power Module (TIPM) and receives electronic ignition switch status messages indicating the ignition switch position over the CAN data bus. The OCM receives ground through a ground circuit and take out of the body wire harness. These connections allow the OCM to be operational whenever the ignition switch is in the ON or START positions.
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 features of the OCS. The most reliable, efficient, and accurate means to diagnose the OCM or the electronic controls and communication related to OCM operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.
REMOVAL
WARNING: To avoid serious or fatal injury, on vehicles equipped with airbags, disable the supplemental restraint system before attempting any steering wheel, steering column, airbag, occupant classification system, seat belt tensioner, impact sensor, or instrument panel component diagnosis or service. Disconnect and isolate the battery negative (ground) cable, then wait two minutes for the system capacitor to discharge before performing further diagnosis or service. This is the only sure way to disable the supplemental restraint system. Failure to take the proper precautions could result in accidental airbag deployment.
NOTE: A non-calibrated Occupant Classification Module (OCM) is available for separate service replacement. The OCM and all of the other components of the Occupant Classification System (OCS) including the passenger side front seat, the seat weight sensors, and the passenger seat adjusters, cushion, back, frame, foam, springs, and wiring harness are a factory-calibrated and assembled unit. Any time any one of these components is removed or replaced for any reason, the OCM must be re-calibrated using a diagnostic scan tool, the Occupant Classification Seat Weight special tool, and the Occupant Classification System Verification Test. Refer to the appropriate diagnostic procedures.
1. Disconnect and isolate the battery negative cable. Wait two minutes for the system capacitor to discharge before further service.
2. Reach under the front edge of the passenger side front seat cushion to access and disconnect the two seat wire harness connectors (3) from the Occupant Classification Module (OCM) (1) connector receptacles located on the left end of the module.
3. Remove the screw (2) that secures the OCM to the underside of the passenger side front seat cushion pan.
4. Slide the OCM forward far enough to disengage the mounting tab from the slot in the dimpled pocket formation (4) in the seat cushion pan.
5. Remove the OCM from under the passenger side front seat.
INSTALLATION
WARNING: To avoid serious or fatal injury, on vehicles equipped with airbags, disable the supplemental restraint system before attempting any steering wheel, steering column, airbag, occupant classification system, seat belt tensioner, impact sensor, or instrument panel component diagnosis or service. Disconnect and isolate the battery negative (ground) cable, then wait two minutes for the system capacitor to discharge before performing further diagnosis or service. This is the only sure way to disable the supplemental restraint system. Failure to take the proper precautions could result in accidental airbag deployment.
NOTE: A non-calibrated Occupant Classification Module (OCM) is available for separate service replacement. The OCM and all of the other components of the Occupant Classification System (OCS) including the passenger side front seat, the seat weight sensors, and the passenger seat adjusters, cushion, back, frame, foam, springs, and wiring harness are a factory-calibrated and assembled unit. Any time any one of these components is removed or replaced for any reason, the OCM must be re-calibrated using a diagnostic scan tool, the Occupant Classification Seat Weight special tool, and the Occupant Classification System Verification Test. Refer to the appropriate diagnostic procedures.
1. Reach under the front edge of the passenger side front seat cushion to carefully position the Occupant Classification Module (OCM) (1) to the underside of the seat cushion pan. When the OCM is correctly positioned, the connector receptacles on the module will be pointed toward the left side of the seat.
2. Slide the OCM rearward far enough to engage the mounting tab into the slot in the dimpled pocket formation (4) in the seat cushion pan.
3. Install and tighten the screw (2) that secures the OCM to the seat cushion pan. Tighten the screw to 2 N·m (20 in. lbs.).
4. Reconnect the two seat wire harness connectors (3) to the OCM connector receptacles located on the left end of the module. Be certain that the latches on each connector are fully engaged.
5. Do not reconnect the battery negative cable at this time. The supplemental restraint system verification test procedure should be performed following service of any supplemental restraint system component. (Refer to 8 - ELECTRICAL/RESTRAINTS - STANDARD PROCEDURE - VERIFICATION TEST).
6. Following successful completion of the supplemental restraint system verification test procedure, perform the Occupant Classification System Verification Test using a diagnostic scan tool. Refer to the appropriate diagnostic procedures.