OCCUPANT CLASSIFICATION MODULE
DESCRIPTION
The Occupant Classification Module (OCM) (1) is
secured to the passenger side outboard front seat
track riser. 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 and all of the other components of the
Occupant Classification System (OCS) including the
passenger side front seat, the seat weight sensors,
the passenger or driver seat track position sensor 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 com-
ponents 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 9077, and the Occupant Classification System
Verification Test. Refer to the appropriate diagnostic
procedures.
The OCM cannot be adjusted or repaired and, if damaged or faulty, 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 mod-
ules 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
(DLC) located on the driver side lower edge of the instrument panel.
The OCM provides voltage to the four seat weight sensors located on each of the four corners of the passenger
side front seat, and to the seat track position sensors located on the passenger and driver front seat tracks. The
OCM then monitors return inputs from each of the sensors on dedicated hard wired data communication circuits.
The seat weight sensor input allows the OCM to determine whether the passenger 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
sensor provides an additional logic input to the OCM microprocessor that allows it to determine the position of the
front seat passenger and driver relative to the front airbags.
Pre-programmed decision algorithms and OCS calibration allow the OCM microprocessor to determine when pas-
senger 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 enables or disables the deployment cir-
cuits 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 classi-
fication 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 DTC’s, if a fault does not recur for a
PM
RESTRAINTS - SERVICE INFORMATION
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