Liberty 2WD L4-2.4L VIN 1 (2005)
Memory Positioning Module: Description and Operation
Occupant Classification Module
The Occupant Classification Module (OCM) is secured with two screws to a stamped steel mounting bracket welded onto the underside of the passenger
side front seat cushion frame near the inboard front corner. 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. The
OCM software is flash programmable.
Two mounting tabs, a connector lock tower, and a connector receptacle are integral to the OCM housing. The connector receptacle contains terminal
pins that connect the OCM to the vehicle electrical system through a dedicated take out and connector of the passenger side front seat wire harness. A
molded plastic lock pin is integral to one end of a long tether, while the other end of the tether is secured to the seat wire harness. After the wire harness
has been connected to the module, the lock pin is engaged through the lock tower on the module housing preventing the connector latches from
becoming disengaged and ensuring that a secure electrical connection is maintained at all times.
A non-calibrated OCM is the only component of the Occupant Classification System (OCS) that is available for separate service replacement. The OCS
components of the passenger side front seat cushion including the cushion frame, springs, insulator pad, seat weight bladder and pressure sensor, seat
cushion foam, wiring harness and the OCM are a factory-calibrated and assembled unit. Once this unit is connected to a vehicle electrically, the
calibration settings are uploaded from the calibrated OCM and stored in the memory of the ACM. If only the OCM is subsequently replaced, the new,
non-calibrated OCM learns the proper calibration settings from the ACM after it is connected to the vehicle electrically.
The OCM cannot be adjusted or repaired and, if damaged or faulty, it must be replaced. The components of the passenger side front seat cushion
including the cushion frame, springs, insulator pad, seat weight bladder and pressure sensor, seat cushion foam, wire harness and the OCM are serviced
only as a factory-calibrated, assembled and tamper-evident unit. Only the OCM and the seat cushion trim are available for separate service replacement.
Once a service replacement package has been installed in a vehicle, the OCM can thereafter be serviced only by replacing the entire passenger side front
seat cushion unit with another complete service replacement package.
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
Programmable Communications Interface (PCI) 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 a nominal five volts to both the pressure sensor of the seat weight bladder beneath the passenger side front seat cushion and to the
belt tension sensor on the passenger side front seat belt lower anchor through dedicated hard wired sensor voltage and sensor ground circuits. The OCM
then monitors the return voltage from each of the sensors on dedicated hard wired data communication circuits. The bladder pressure sensor input allows
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 cushion. The belt tension sensor provides an additional logic input to the OCM microprocessor that allows it to distinguish between
the lower seat belt cinch loads of a belted occupant and the higher loads associated with a belted child seat.
Pre-programmed decision algorithms and OCS calibration allow the OCM microprocessor to determine when passenger airbag protection is appropriate
based upon the seat cushion load as signaled by the bladder pressure sensor and the seat belt cinch load as signaled by the belt tension sensor. When the