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
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.
In models not equipped with a rear seat, 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 airbag indicator driver circuit. If the pas-
senger 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 passen-
ger airbag from being deployed if an impact is
detected that is sufficient for an airbag deployment.
The ACM also turns on the on/off switch Off indica-
tor for about seven seconds 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 passen-
ger airbag on/off switch circuits, and will turn on the
airbag indicator in the EMIC if a fault has been
detected.
The ACM receives battery current through two cir-
cuits; a fused ignition switch output (run) circuit
through a fuse in the fuse block, and a fused ignition
switch output (run-start) circuit through a second
fuse in the fuse block. The ACM receives ground
through a ground circuit and take out of the body
wire harness. This take out has a single eyelet ter-
minal connector that is secured by a ground screw to
the right cowl side inner panel below the instrument
panel. These connections allow the ACM to be opera-
tional whenever the ignition switch is in the Start or
On positions. The ACM also contains an energy-stor-
age capacitor. When the ignition switch is in the
Start or On positions, this capacitor is continually
being charged with enough electrical energy to
deploy the front supplemental restraint components
for up to one second following a battery disconnect or
failure. The purpose of the capacitor is to provide
backup supplemental restraint system protection in
case there is a loss of battery current supply to the
ACM during an impact.
Two sensors are contained within the ACM; an
electronic impact sensor, and a safing sensor. The
electronic impact sensor is an accelerometer that
senses the rate of vehicle deceleration, which pro-
vides verification of the direction and severity of an
impact. The safing sensor is an electromechanical
sensor within the ACM that provides an additional
logic input to the ACM microprocessor. The safing
sensor is a normally open switch that is used to ver-
ify the need for a front supplemental restraint
deployment by detecting impact energy of a lesser
magnitude than that of the electronic impact sensor,
and must be closed in order for the front airbags to
deploy. A pre-programmed decision algorithm in the
ACM microprocessor determines when the decelera-
tion rate as signaled by the impact sensor and the
safing sensor indicate an impact that is severe
enough to require front supplemental restraint sys-
tem protection and, based upon the status of the pas-
senger airbag on/off switch input and the severity of
the monitored impact, determines what combination
of front airbag deployment is required for each front
seating position. When the programmed conditions
are met, the ACM sends the proper electrical signals
to deploy the dual front airbags.
The hard wired inputs and outputs for the ACM
may be diagnosed and tested using conventional
diagnostic tools and procedures. However, conven-
tional diagnostic methods will not prove conclusive in
the diagnosis of the ACM, the PCI data bus network,
or the electronic message inputs to and outputs from
the ACM. The most reliable, efficient, and accurate
means to diagnose the ACM, the PCI data bus net-
work, and the electronic message inputs to and out-
puts from the ACM requires the use of a DRBIII
t
scan tool. Refer to the appropriate diagnostic infor-
mation.
TJ
RESTRAINTS
8O - 9
AIRBAG CONTROL MODULE (Continued)