OCCUPANT CLASSIFICATION MODULE
DESCRIPTION
The Occupant Classification Module (OCM) (1) 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 mod-
ule housing is sealed to enclose and protect the inter-
nal electronic circuitry. The OCM software is flash
programmable.
Two mounting tabs (4), a connector lock tower (2), and a connector receptacle (3) 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 sep-
arate 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 subse-
quently replaced, the new, non-calibrated OCM learns the proper calibration settings from the ACM after it is con-
nected 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 pres-
sure 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.
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 mod-
ules 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 pas-
senger 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 occu-
pant by providing a weight-sensing reference to the load on the seat cushion. The belt tension sensor provides an
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RESTRAINTS - SERVICE INFORMATION
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