Air Bag Control Module: Description and Operation

AIRBAG SYSTEM/OCCUPANT RESTRAINT CONTROLLER SYSTEM
The Airbag system is equipped with a new type of Airbag Control Module (ACM) called an Occupant Restraint Controller (ORC). The ACM is secured to a bracket on the floor panel transmission tunnel between the floor shifter and parking brake. The ACM contains a microprocessor, the impact sensor, and energy storage capacitors. The microprocessor contains the airbag system logic. The airbag system logic includes On-Board Diagnostics OBD capability, and communicates with the instrument cluster circuitry on the Programmable Communication Interface (PCI) data bus to control the airbag indicator lamp. 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 Mechanical Instrument Cluster (MIC) over the PCI data bus to turn ON the airbag warning lamp. A pre-programmed decision algorithm in the ACM microprocessor determines when the deceleration rate 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. This capacitor stores enough electrical energy to deploy the airbags, for two minutes following a battery disconnect or failure during an impact. The purpose of the capacitor is to provide airbag system protection in severe secondary impact if the initial impact has damaged or disconnected the battery, but not severe enough to deploy the airbags. The ACM cannot be repaired or adjusted and, if damaged or faulty, it must be replaced.

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. 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 OCCUPANT RESTRAINT CONTROLLER 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 lamp ON for 6 - 8 seconds. If the lamp remains OFF; 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 ACM system or the MIC lamp circuit may be internally shorted to ground.

SIDE IMPACT AIRBAG CONTROL MODULES
They are located on the left and right B-post. The SIACM perform self diagnostics and circuit tests to determine if the system is functioning properly. If the test finds a problem the SIACM will set both active and stored diagnostic trouble codes. If a DTC is active the SIACM will request that the airbag warning lamp be turned ON. The results of the system test are transmitted on the PCI Bus to the ACM once each second or on change in lamp state. If the warning lamp status message from the either SIACM contains a lamp ON request the ACM will set an active DTC. At the same time as the DTC is set the ACM sends a PCI Bus message to the Mechanical Instrument Cluster (MIC) requesting the airbag warning lamp be turned ON. Observe all ACM warning and caution statements when servicing or handling the SIACM. SIACM are not repairable and must be replaced if they are dropped.

SEAT AIRBAG MODULES
The Left and Right seat airbags are located in the outboard end of the front seat backs. The airbag module contains a bag, an inflator (a small canister of highly compressed argon gas) and a mounting bracket. The seat airbag module cannot be repaired and must be replaced if deployed or in any way damaged. When supplied with the proper electrical signal the inflator seals the hole in the airbag cushion so it can discharge the compressed gas it contains directly into the cushion. Upon deployment, the seat back trim cover will tear open and allow the seat airbag to fully deploy between the seat and the door.

NOTE: It will be necessary to remove the seat back trim to gain access to the seat airbag module connector when diagnosing the seat airbag system.

WARNING: THE SEAT AIRBAG MODULE CONTAINS ARGON GAS PRESSURIZED TO OVER 2500 PSI. DO NOT ATTEMPT TO DISMANTLE AN AIRBAG MODULE OR TAMPER WITH ITS INFLATOR. DO NOT PUNCTURE, INCINERATE, OR BRING INTO CONTACT WITH ELECTRICITY. DO NOT STORE AT TEMPERATURE EXCEEDING 93 °C (200 °F). REPLACE AIRBAG SYSTEM COMPONENTS ONLY WITH PARTS SPECIFIED IN THE CHRYSLER MOPAR PARTS CATALOG. SUBSTITUTE PARTS MAY APPEAR INTERCHANGEABLE, BUT INTERNAL DIFFERENCES MAY RESULT IN INFERIOR OCCUPANT PROTECTION. THE FASTENERS, SCREWS, AND BOLTS ORIGINALLY USED FOR THE AIRBAG SYSTEM COMPONENTS HAVE SPECIAL COATINGS AND ARE SPECIFICALLY DESIGNED FOR THE AIRBAG SYSTEM. THEY MUST NEVER BE REPLACED WITH ANY SUBSTITUTES. ANY TIME A NEW FASTENER IS NEEDED, REPLACE IT WITH THE CORRECT FASTENERS PROVIDED IN THE SERVICE PACKAGE OR SPECIFIED IN THE CHRYSLER MOPAR PARTS CATALOG.

DIAGNOSTIC TROUBLE CODES
Airbag diagnostic trouble codes consist of active and stored codes. If more than one code exists, diagnostic priority should be given to the active codes.

Each diagnostic trouble code is diagnosed by following a specific testing procedure. The diagnostic test procedures contain step-by-step instructions for determining the cause of the trouble codes. It is not necessary to perform all of the tests in this book to diagnose an individual code.

Active diagnostic trouble codes for the airbag system are not permanent and will change the moment the reason for the code is corrected. In certain test procedures within this manual, diagnostic trouble codes are used as a diagnostic tool.

Active Codes
The code becomes active as soon as the malfunction is detected or key-off, whichever occurs first. An active trouble code indicates an on-going malfunction. This means that the malfunction is currently there every time the control module checks that circuit/function. It is impossible to erase an active code; active codes automatically erase by themselves when the reason for the code has been corrected.

With the exception of the warning lamp trouble codes or malfunctions, when a malfunction is detected, the airbag lamp remains lit for a minimum of 12 seconds or as long as the malfunction is present.

An "Interrogate Right SIACM or Interrogate left SIACM" diagnostic trouble code indicates an active trouble code in the respective module.

Stored Codes
Airbag codes are automatically stored in the ACM's memory as soon as the malfunction is detected. A "stored" code indicates there was an active code present at some time. However, the code currently may not be present as an active code, although another active code could be.

When a trouble code occurs, the airbag warning lamp illuminates for 12 seconds minimum (even if the problem existed for less than 12 seconds). The code is stored, along with the time in minutes it was active, and the number of times the ignition has been cycled since the problem was last detected. The minimum time shown for any code will be one minute, even if the code was actually present for less than one minute. Thus, the time shown for a code that was present for two minutes 13 seconds, for example, would be three minutes.

If a malfunction is detected a diagnostic trouble code is stored and will remain stored as long as the malfunction exists. When and if the malfunction ceases to exist, an ignition cycle count will be initiated for that code. If the ignition cycle count reaches 100 without a reoccurrence of the same malfunction, the diagnostic trouble code is erased and that ignition cycle counter is reset to zero. If the malfunction reoccurs before the count reaches 100, then the ignition cycle counter will be reset and the diagnostic trouble code will continue to be a stored code.

If a malfunction is not active while performing a diagnostic test procedure, the active code diagnostic test will not locate the source of the problem. In this case, the stored code can indicate an area to inspect.

If no obvious problems are found, erase stored codes, and with the ignition "ON" wiggle the wire harness and connectors, rotate the steering wheel from stop to stop. Recheck for codes periodically as you work through the system. This procedure may uncover a malfunction that is difficult to locate.

Occupant Restraint System Trouble Codes
The Occupant Restraint System contains three modules ACM, Left SIACM and Right SIACM (If equipped with SIACM) that store active and stored DTC's. Some DTC's will require replacing the implicated module. Other DTC's will require some Diagnostic procedures to determine defective components.