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GENERAL INFORMATION
modules receive all the information transmitted on the
bus even though a module may not require all infor-
mation to perform its function. It will only respond to
messages "addressed" to it through binary coding
process. This method of data transmission signifi-
cantly reduces the complexity of the wiring in the
vehicle and the size of wiring harnesses. All of the
information about the functioning of all the systems is
organized, controlled, and communicated by the PCI
bus, which is described in the Communication Section
of this general information.
3.1 AIRBAG SYSTEM
The 2003 Minivan Airbag System contain the
following components: Occupant Restraint Control-
ler (ORC), Airbag Warning Indicator, Clockspring,
Driver and Passenger Airbags, Seat belt Tensioners
(SBT), Hall-effect Seat Belt Switches (SBS), Left
and Right Side Airbag Control Module (SIACM),
and Seat (mounted side) Airbags.
The Occupant Restraint Controller (ORC) is a
new type of Airbag Control Module (ACM) that
supports staged airbag deployment. Staged deploy-
ment is the ability to trigger airbag system squib
inflators all at once or individually as needed to
provide the appropriate restraint for the severity of
the impact. The ACM has four major functions: PCI
Bus communications, onboard diagnostics, impact
sensing, and component deployment. The ACM also
contains an energy-storage capacitor. This capaci-
tor stores enough electrical energy to deploy the
front airbag components for two seconds following a
battery disconnect or failure during an impact. The
ORC is secured to the floor panel transmission
tunnel below the instrument panel inside the vehi-
cle. The ACM cannot be repaired or adjusted and
must be replaced.
The ACM sends and/or receives PCI Bus mes-
sages with the Instrument Cluster (MIC), Body
Control Module (BCM), and Powertrain Control
Module (PCM). Diagnostic trouble codes will be set
if the communication with these modules is lost or
contains invalid information.
The microprocessor in the ACM monitors the
impact sensor signal and the airbag system electri-
cal circuits to determine the system readiness. The
ACM also monitors bus messages from both SI-
ACM. If the ACM detects a monitored system fault
or SIACM fault, it sends a message to the instru-
ment cluster via PCI bus to turn on the airbag
warning indicator. The ACM can set both active and
stored diagnostic trouble codes to aid in the diag-
nosing system problems. See DIAGNOSTIC TROU-
BLE CODES in this section.
The ACM has an internal accelerometer that
senses the rate of vehicle deceleration, which pro-
vides verification of the direction and severity of an
impact. A pre-programmed decision algorithm in
the ACM microprocessor determines when the de-
celeration rate is severe enough to require airbag
system protection. The ACM also uses the driver
and front passenger seat belt switch status (buckled
or unbuckled) to determine whether or not the seat
belt tensioners should deploy. The ACM also uses
the crash severity to determine the level of driver
and front passenger deployment, low medium or
high. When the programmed conditions are met,
the ACM sends an electrical signal to deploy the
appropriate airbag system components.
WARNING: THE AIRBAG SYSTEM IS A
SENSITIVE,
COMPLEX
MECHANICAL UNIT. BEFORE ATTEMPTING
TO DIAGNOSE OR SERVICE ANY AIRBAG
SYSTEM OR RELATED STEERING WHEEL,
STEERING
COLUMN,
PANEL COMPONENTS YOU MUST FIRST
DISCONNECT AND ISOLATE THE BATTERY
NEGATIVE (GROUND) CABLE. WAIT TWO
MINUTES FOR THE SYSTEM CAPACITOR TO
DISCHARGE BEFORE FURTHER SYSTEM
SERVICE. THIS IS THE ONLY SURE WAY TO
DISABLE THE AIRBAG SYSTEM. FAILURE
TO DO THIS COULD RESULT IS ACCIDENTAL
AIRBAG
DEPLOYMENT
PERSONAL INJURY. NEVER STRIKE OR
KICK THE AIRBAG CONTROL MODULE, AS
IT CAN DAMAGE THE IMPACT SENSOR OR
AFFECT ITS CALIBRATION. IF AN AIRBAG
CONTROL
MODULE
DROPPED DURING SERVICE, THE MODULE
MUST BE SCRAPPED AND REPLACED WITH
A NEW UNIT.
The airbag warning lamp is the only point at
which the customer can observe symptoms of a
system malfunction. Whenever the ignition key is
turned to the run or start position, the MIC per-
forms a lamp check by turning the airbag warning
indicator on for 6-8 seconds. After the lamp check, if
the indicator turns on, it means that the ACM has
checked the system and found it to be free of
discernible malfunctions. If the lamp remains on,
there could be an active fault in the system or the
MIC lamp circuit may be internally shorted to
ground. If the lamp comes on and stays on for a
period longer than 6-8 seconds then goes off, there
is usually an intermittent problem in the system.
2
ELECTRO-
OR
INSTRUMENT
AND
POSSIBLE
IS
ACCIDENTALLY
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