Caravan FWD V6-3.3L VIN 3 Flex Fuel (2001)
Body Control Module: Description and Operation
Part 1 of 5
SIX-STEP TROUBLESHOOTING PROCEDURE
Diagnosis of the body system is done in six basic steps:
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verification of complaint
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verification of any related symptoms
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symptom analysis
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problem isolation
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repair of isolated problem
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verification of proper operation
SYSTEM DESCRIPTION AND FUNCTIONAL OPERATION
The body system on the 2001 RS consists of a combination of modules that communicate over the PCI bus (Programmable Communication
Interface multiplex system). Through the PCI bus, information about the operation of vehicle components and circuits is relayed quickly to the
appropriate module(s). All modules receive all the information transmitted on the bus even though a module may not require all information to
perform its function. It will only respond to messages "addressed" to it through binary coding process. This method of data transmission
significantly 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 of this general information.
AIRBAG SYSTEM/OCCUPANT RESTRAINT CONTROLLER SYSTEM
The 2001 Minivan Airbag System contain the following components: Occupant Restraint Controller (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
deployment 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 ORC has four major functions: PCI Bus communications, onboard diagnostics, impact sensing, and component
deployment. The ORC also contains an energy-storage capacitor. This capacitor 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 vehicle. The ORC cannot be repaired or adjusted and must be replaced.
The ORC sends and/or receives PCI Bus messages 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 ORC monitors the impact sensor signal and the airbag system electrical circuits to determine the system readiness. The
ORC also monitors bus messages from both SIACM. If the ORC detects a monitored system fault or SIACM fault, it sends a message to the
instrument cluster via PCI bus to turn on the airbag warning indicator. The ORC can set both active and stored diagnostic trouble codes to aid in
the diagnosing system problems. See ORC/SIACM DIAGNOSTIC TROUBLE CODES.
The ORC has an internal accelerometer that senses the rate of vehicle deceleration, which provides verification of the direction and severity of an
impact. A pre-programmed decision algorithm in the ORC microprocessor determines when the deceleration rate is severe enough to require
airbag system protection. The Occupant Restraint Controller (ORC) also uses the driver and front passenger seat belt switch status (buckled or
unbuckled) as inputs to determine the level of airbag deployment, low, medium, or high as well as whether or not the seat belt tensioners should
deploy. The ORC 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 ORC sends an electrical signal to deploy the appropriate airbag system components.
WARNING: THE AIRBAG SYSTEM IS A SENSITIVE, COMPLEX ELECTRO-MECHANICAL UNIT. BEFORE ATTEMPTING TO
DIAGNOSE OR SERVICE ANY AIRBAG SYSTEM OR RELATED STEERING WHEEL, STEERING COLUMN, OR INSTRUMENT
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 AND POSSIBLE 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 IS
ACCIDENTALLY 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 performs 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 ORC 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.
Driver Airbag
The airbag protective trim cover is the most visible part of the driver side airbag system. The protective trim cover is fitted to the front of the
airbag module and forms a decorative cover in the center of the steering wheel. The module is mounted directly to the steering wheel. Located
under the trim cover are the horn switch, the airbag cushion, and the airbag cushion supporting components. The airbag module includes a housing
