RAM 2500 Truck 2WD L6-5.9L DSL Turbo VIN C (2002)
Body Control Module: Description and Operation
Airbag System
AIRBAG SYSTEM
The Airbag Control Module (ACM) is secured to a bracket on the floor panel transmission tunnel below the instrument panel inside the vehicle. The
ACM mounting bracket also serves as the instrument panel center support. The ACM contains a microprocessor, the impact sensor, and energy storage
capacitor. The microprocessor contains the airbag system logic. The ACM system logic includes On-Board Diagnostics (OBD) capability, and
communicates with the instrument cluster circuitry on the Chrysler Collision Detection (CCD) data bus to control the airbag indicator lamp.
The mircoprocessor in the ACM monitors the impact sensor signal and the airbag system electrical circuits to determine the system readiness. If the
ACM detects a monitored system fault, it sends messages to the instrument cluster on the CCD data bus to turn ON the airbag indicator lamp. A
pre-programmed decision algorithm in the ACM microprocessor determines when the deceleration rate signaled by the impact sensor indicates an impact
that is severe enough to require airbag system protection. When the programmed conditions are met, the ACM sends an electrical signal to deploy the
airbag system components.
Only one impact sensor is used in this airbag system. The impact sensor is an accelerometer that senses the rate of vehicle deceleration, which provides
verification of the direction and severity of an impact. The impact sensor is calibrated for the specific vehicle, and is only serviced as a unit with the
ACM.
The ACM also contains and energy-storage capacitor. This capacitor stores enough electrical energy to deploy the airbags, for one second following a
battery disconnect or failure during an impact. The purpose of the capacitor is to provide airbag system protection in a severe secondary impact if the
initial impact has damaged or disconnected the battery, but was not severe enough to deploy the airbags.
WARNING: THE AIRBAG SYSTEM IS A SENSITIVE, COMPLEX ELECTROMECHANICAL 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.
THEN 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 IN 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 Mechanical Instrument Cluster (MIC) performs a lamp check by turning the AIRBAG warning lamp ON for 6-8
seconds. If the lamp remains OFF, 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.
The MIC monitors the airbag warning lamp and seat belt warning lamp during the bulb check for a defective bulb or lamp driver circuit. The MIC tests
the airbag lamp during the cluster bulb check and substitutes the seat belt lamp if the airbag lamp is defective. If the airbag lamp is defective the MIC
will turn the seat belt light ON and OFF approximately 30 times to warn the driver that the airbag lamp is defective. The lamp status is sent to the ACM
continuously via a CCD bus message. The seat belt lamp acts as a backup in the event that the AIRBAG lamp is defective. This information is sent to the
ACM continuously via a CCD bus message.
Perform the WARNING INDICATOR procedures to find the cause of any customer complaint regarding the AIRBAG warning indicator.
The ACM cannot be repaired or adjusted and, if damaged or faulty, it must be replaced.
Driver Airbag Module (DAB)
The airbag protective trim cover is the most visible part of the driver side airbag system. 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 to
which the cushion and inflator are attached and sealed. The airbag module cannot be repaired, and must be replaced if deployed or in any way damaged.
The inflator assembly is mounted to the back of the airbag module. The inflator seals the hole in the airbag cushion so it can discharge the gas it
produces directly into the cushion when supplied with the proper electrical signal. 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. Upon airbag deployment, this cover will split at a predetermined breakout line.
WARNING: THE AIRBAG MODULE INFLATOR ASSEMBLY CONTAINS SODIUM AND POTASSIUM NITRATE.
THESE MATERIALS ARE POISONOUS AND EXTREMELY FLAMMABLE. CONTACT WITH ACID, WATER, OR HEAVY
