The supplemental restraint system electrical circuits are continuously monitored and controlled by a microprocessor
and software contained within the Airbag Control Module (ACM). An airbag indicator in the ElectroMechanical Instru-
ment Cluster (EMIC) illuminates for about seven seconds as a bulb test each time the ignition switch is turned to the
On or Start positions. Following the bulb test, the airbag indicator is turned on or off by the ACM to indicate the
status of the supplemental restraint system. If the airbag indicator comes on at any time other than during the bulb
test, it indicates that there is a problem in the supplemental restraint system electrical circuits. Such a problem may
cause airbags not to deploy when required, or to deploy when not required.
Deployment of the supplemental restraints depends upon the angle and severity of an impact. Deployment is not
based upon vehicle speed; rather, deployment is based upon the rate of deceleration as measured by the forces of
gravity (G force) upon the impact sensors. When an impact is severe enough, the microprocessor in the ACM sig-
nals the inflator of the appropriate airbag units to deploy their airbag cushions. The front seat belt tensioners are
provided with a deployment signal by the ACM in conjunction with the front airbags.
During a frontal vehicle impact, the knee blockers work in concert with properly fastened and adjusted seat belts to
restrain both the driver and the front seat passenger in the proper position for an airbag deployment. The knee
blockers also absorb and distribute the crash energy from the driver and the front seat passenger to the structure
of the instrument panel. The seat belt tensioners remove the slack from the front seat belts to provide further assur-
ance that the driver and front seat passenger are properly positioned and restrained for an airbag deployment.
Typically, the vehicle occupants recall more about the events preceding and following a collision than they do of an
airbag deployment itself. This is because the airbag deployment and deflation occur very rapidly. In a typical 48
kilometer-per-hour (30 mile-per-hour) barrier impact, from the moment of impact until the airbags are fully inflated
takes about 40 milliseconds. Within one to two seconds from the moment of impact, the airbags are almost entirely
deflated. The times cited for these events are approximations, which apply only to a barrier impact at the given
speed. Actual times will vary somewhat, depending upon the vehicle speed, impact angle, severity of the impact,
and the type of collision.
When the ACM monitors a problem in any of the dual front airbag system circuits or components, including the seat
belt tensioners, it stores a fault code or Diagnostic Trouble Code (DTC) in its memory circuit and sends an elec-
tronic message to the EMIC to turn on the airbag indicator. Proper testing of the supplemental restraint system
components, the Programmable Communications Interface (PCI) data bus, the electronic message inputs to and
outputs from the EMIC or the ACM, as well as the retrieval or erasure of a DTC from the ACM or the EMIC requires
the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.
See the owner’s manual in the vehicle glove box for more information on the features, use and operation of all of
the factory-installed passive restraints.
OCCUPANT CLASSIFICATION SYSTEM
Vehicles manufactured for the North American market are equipped with the Occupant Classification System (OCS).
The OCS automatically suppresses or enables passenger airbag and seat belt tensioner operation based upon
whether or not the passenger side front seat is occupied and, if the seat is occupied, classifies the size of the
occupant and whether the seat is occupied by a child seat.
The OCS has an Occupant Classification Module (OCM) that monitors inputs from the seat weight bladder pressure
sensor under the passenger side front seat cushion and from the belt tension sensor on the passenger side front
seat belt lower anchor. Based upon those inputs the microprocessor within the OCM classifies the occupant of the
passenger side front seat. The OCM then sends electronic occupant classification messages to the Airbag Control
Module (ACM). The microprocessor and programming of the ACM determines whether to enable or disable the
deployment circuits for the passenger airbag and seat belt tensioner; and, if enabled, what force level should be
used to deploy each front airbag.
The OCS electrical circuits and components are continuously monitored by the OCM, and the OCM is continuously
monitored by the ACM. A passenger airbag on/off indicator is located in the inboard end cap of the instrument panel
grab handle. This indicator receives battery current whenever the ignition switch is in the On or Start positions, and
illuminates only when the ACM pulls the indicator control circuit to ground. The indicator illuminates for about seven
seconds as a bulb test each time the ignition switch is turned to the On or Start positions. Following the bulb test,
the indicator is turned on or off by the ACM based upon the electronic occupant classification messages received
from the OCM. This indicator is illuminated whenever the passenger airbag and seat belt tensioner operation has
been suppressed, and is turned off whenever the seat is empty or when the seat is occupied and the passenger
airbag and seat belt tensioner are enabled.
When the OCM monitors a problem in any of the OCS circuits or components, it stores a fault code or DTC in its
memory circuit and sends an electronic message to the ACM. The ACM then sends an electronic message to the
8O - 242
RESTRAINTS - SERVICE INFORMATION
KJ