Airbag Control Module Description; Operation - Dodge dakota 2002 Service Manual

8O - 10 RESTRAINTS
AIRBAG CONTROL MODULE
DESCRIPTION
Fig. 7 Airbag Control Module
1 - AIRBAG CONTROL MODULE
2 - ORIENTATION ARROW
3 - CONNECTOR RECEPTACLE
The Airbag Control Module (ACM) is secured with
four screws to the top mounting surface of a stamped
steel 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 (Fig. 7). 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 elec-
tromechanical 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.
The ACM housing has integral mounting flanges
on each side. Two of the mounting flanges, one on
each side, have an integral locating pin on their
lower surface. The left flanges have round mounting
holes, while the flanges on the right side have slotted
mounting holes. An arrow cast into the top of the
ACM housing near the rear provides a visual verifi-
cation of the proper orientation of the unit, and
should always be pointed toward the front of the
vehicle. A molded plastic electrical connector recepta-
cle containing twenty-three terminal pins exits the
rearward facing side of the ACM housing. These ter-
minal pins connect the ACM to the vehicle electrical
system through a dedicated take out and connector of
the instrument panel wire harness.
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.

OPERATION

The microprocessor in the Airbag Control Module
(ACM) contains the front supplemental restraint sys-
tem logic circuits and controls all of the front supple-
mental 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 Programma-
ble Communications Interface (PCI) data bus net-
work. This method of communication is used for
control of the airbag indicator in the ElectroMechani-
cal 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 8 -
ELECTRICAL/INSTRUMENT
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.
In standard cab models, the ACM also monitors a
resistor multiplexed input from the passenger airbag
on/off switch and provides a control output for the
Off indicator in the switch through a passenger air-
bag indicator driver circuit. If the passenger airbag
on/off switch is set to the Off position, the ACM turns
on the passenger airbag on/off switch Off indicator
and will internally disable the passenger airbag from
being deployed if an impact is detected that is suffi-
cient for an airbag deployment. The ACM also turns
on the on/off switch Off indicator for about seven sec-
onds each time the ignition switch is turned to the
On position as a bulb test. Following the bulb test,
the ACM controls the status of the Off indicator
based upon the resistance of the input from the on/off
switch. The ACM will also set and/or store a DTC for
faults it detects in the passenger airbag on/off switch
circuits, and will turn on the airbag indicator in the
EMIC if a fault has been detected.
DR
CLUSTER/AIRBAG