Neon R/T L4-2.0L VIN F HO (2001)
Air Bag Control Module: Description and Operation
Airbag Control Module (ACM)
Fig.3 Airbag Control Module (ACM) Location
AIRBAG CONTROL MODULE
The Airbag Control Module (ACM) contains the sensing element, safing sensor, and energy reserve capacitor. The module is mounted on the
tunnel/floor pan between the gear shift lever and the park brake lever. 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 via the PCI data bus to control the airbag indicator lamp. The warning equipment is tested for 6
- 8 seconds every time the vehicle is started and will illuminate the AIRBAG warning lamp in the cluster when a fault occurs.
The microprocessor 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 PCI data bus to turn on the airbag indicator lamp. A
preprogrammed decision algorithm in the ACM micro- processor determines when the deceleration rate as signaled by the 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.
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 an energy-storage capacitor. 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.
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. 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 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 lamp ON for 6 - 8 seconds. If the lamp
turns 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 ACM cannot be repaired or adjusted and, if damaged or faulty, it must be replaced.
