Liberty Sport 2WD L4-2.4L VIN 1 (2002)
Air Bag Control Module: Description and Operation
Fig.6 Airbag Control Module
AIRBAG CONTROL MODULE
The Airbag Control Module (ACM) is also sometimes referred to as the Occupant Restraint Controller (ORC). The ACM is secured with two
long screws within a tray-like stamped steel mounting bracket welded onto the top of the floor panel transmission tunnel forward of the instrument
panel center support bracket and below the instrument panel center stack in the passenger compartment of the vehicle.
Concealed within a hollow in the center of the die cast aluminum ACM housing is the electronic circuitry of the ACM which includes a
microprocessor, an electronic impact sensor, an electromechanical safing sensor, and an energy storage capacitor. A stamped metal cover plate is
secured to the bottom of the ACM housing with four screws to enclose and protect the internal electronic circuitry and components. An arrow cast
into the top of the ACM housing near the front provides a visual verification of the proper orientation of the unit, and should always be pointed
toward the front of the vehicle.
The ACM housing also has an integral ground lug with a tapped hole that protrudes from the lower left rear corner of the unit. This lug provides a
case ground to the ACM when a ground screw is installed through the left side of the mounting bracket. Two molded plastic electrical connector
receptacles exit the right side of the ACM housing. The smaller of the two receptacles contains twelve terminal pins, while the larger one contains
twenty-three. These terminal pins connect the ACM to the vehicle electrical system through two dedicated take outs and connectors of the
instrument panel wire harness.
A molded rubber protective cover is installed loosely over the ACM to protect the unit from condensation or coolant leaking from a damaged or
faulty heater-air conditioner unit housing. An integral flange on the left side of the cover is secured to the floor panel transmission tunnel with a
short piece of double-faced tape as an assembly aid during the manufacturing process, but this tape does not require replacement following service
removal.
The impact sensor and safing sensor internal to the ACM are calibrated for the specific vehicle, and are only serviced as a unit with the ACM. The
ACM cannot be repaired or adjusted and, if damaged or faulty, it must be replaced. The ACM cover is available for separate service replacement.
The microprocessor in the Airbag Control Module (ACM) contains the front supplemental restraint system logic circuits and controls all of the
front supplemental restraint system components. The ACM uses On-Board Diagnostics (OBD) and can communicate with other electronic
modules in the vehicle as well as with the DRBIII scan tool using the Programmable Communications Interface (PCI) data bus network. This
method of communication is used for control of the airbag indicator in the ElectroMechanical Instrument Cluster (EMIC) and for supplemental
restraint system diagnosis and testing through the 16-way data link connector located on the driver side lower edge of the instrument panel. (Refer
to INSTRUMENT CLUSTER/AIRBAG INDICATOR - OPERATION).
The ACM microprocessor continuously monitors all of the front supplemental restraint system electrical circuits to determine the system readiness.
If the ACM detects a monitored system fault, it sets an active and stored Diagnostic Trouble Code (DTC) and sends electronic messages to the
EMIC over the PCI data bus to turn on the airbag indicator. An active fault only remains for the duration of the fault or in some cases the duration
of the current ignition switch cycle, while a stored fault causes a DTC to be stored in memory by the ACM. For some DTCs, if a fault does not
recur for a number of ignition cycles, the ACM will automatically erase the stored DTC. For other internal faults, the stored DTC is latched
forever.
