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Air Bag Systems: Description and Operation

AIRBAG SYSTEMS
The airbag system was designed to provide increased driver and passenger protection if the vehicle is involved in a front-end collision. The system was designed to be, and is most effective when used in conjunction with the seat belt system. The passenger side airbag assembly utilizes a canister of compressed, inert gas to inflate the bag. This gas is expanded at a very high rate through a heating process, that allows a small quantity of gas under a very high pressure to inflate the large passenger airbag.

The Prowler utilizes two front impact sensors, located on each side of the battery and a safing sensor located in the ACM to control the deployment of the airbags. Diagnosis of the system is done through the Data Link Connector (DLC) located under and just to the left of the steering column.

The airbag lamp is located in the cluster. Whenever the ignition key is turned to the "run" position, the cluster illuminates the bulb for 7 seconds. This illumination is called bulb prove-out. After the 7 seconds, the bulb will normally extinguish. The bulb will illuminate if the ACM senses a fault in the Airbag system and communicates this message to the cluster via the CCD bus. The cluster will also light the light if the ACM fails to communicate with it for 5 consecutive seconds. If for some reason the cluster illuminates the airbag lamp, it will keep the lamp illuminated for a minimum of 12 seconds. This lamp is not dimmable.

The ACM monitors critical input and output circuits within the airbag system, making sure they are operating correctly. Some circuits are tested continuously; others are checked only under certain circumstances. The ACM provides diagnostic information about the airbag system to the technician through the DRBIII(R) via the CCD bus.

The deceleration or g-force resulting from the impact of a front-end collision causes the front sensors to close. The safing sensor is designed to close from much lower g-forces than the front sensors. As soon as one of the front impact sensors and the safing sensor are closed, an electrical charge is sent to the airbag module. This causes the inflator to be actuated, thus deploying the airbags. The total time from the closure of the sensors to deployment and deflation of the airbags is less than 1/10 of one second.

The ACM also contains an energy storage capacitor. This capacitor stores enough electrical energy to deploy the airbags for up to two minutes following a battery disconnect or failure. The purpose of the capacitor is to provide airbag deployment 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 warning lamp is the only point at which "symptoms" of a system malfunction can be observed by the customer.

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.

Active Codes
An active trouble code indicates an on-going malfunction. This means the defect is there every time the ACM checks that circuit/function. It is impossible to erase an active code; active codes are automatically erased by the ACM when the reason for the code has been corrected.

Stored Codes
Airbag codes are continuously stored in the ACM's memory when the ignition is turned OFF with the exception of the Loss of Ignition Run Only code, which is an active code only.

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 that 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 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 the code is stored and an ignition cycle count will be initiated for the code. If the ignition cycle count reaches 100 without reoccurrence of that same malfunction, that 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 the stored code, 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.