Air Bag Systems: Description and Operation

AIRBAG SYSTEM
The airbag system is designed to provide increased driver and passenger protection if the vehicle is involved in a front end collision. The system is most effective when used in conjunction with the seat belt system.

Both driver and passenger side airbag assemblies are now hybrid type which utilize a canister of compressed, inert gas to inflate the bag, instead of sodium azide.

Currently, Chrysler Corporation uses two types of airbag control modules. The ASDM system is a mechanically-triggered system utilizing two front impact sensors and a sensor inside the module. The AECM (AB, JX, JA and NS bodies only) is an electronically-triggered system that uses only its own internal electronic sensor to trigger the airbags. This will address the AECM type of module, the term "Airbag Control Module" (or ACM) will be used to refer to the module.

Functional Operation
Whenever the ignition key is turned to the "RUN" or "START" position, the airbag control module (ACM) performs a lamp check by turning the AIRBAG warning lamp on. The lamp stays lit for 6 - 8 seconds, then goes off. If the lamp remains off, it means that the ACM has checked the system and found it to be free of discernible malfunctions. The airbag system is monitored by the ACM.

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 DRB III via the CCD bus.

The deceleration or g-force resulting from the impact of a front-end collision causes the electronic sensor inside of the ACM to be triggered. This causes the inflators to be actuated, thus deploying the airbags. The total time between determining to deploy and full inflation of the airbag is approximately 40 ms.

A new enhanced accident response feature has been added. This feature, upon deployment of the airbag, turns on the interior lights and unlocks the power door locks (if equipped).

The AIRBAG warning lamp is the only point at which "symptoms" of a system malfunction can be observed by the customer.

Use the test procedures in this book to find the cause of any customer complaint regarding the AIRBAG warning lamp,such as:
- warning lamp does not come on at all
- warning lamp stays on

AIRBAG CONTROL MODULE (ACM)

Airbag Control Module (ACM) Location:

The driver and passenger airbag system is a safety device designed to reduce the risk of fatality or serious injury, caused by a frontal impact of the vehicle.

The Airbag Control Module (ACM) contains the impact sensor and energy reserve capacitor. The ACM monitors the system to determine the system readiness. The ACM contains on-board diagnostics and will light the AIRBAG warning lamp in the message center when a problem occurs.

The impact sensor provides verification of the direction and severity of the impact. One impact sensor is used. It is located inside the Airbag Control Module (ACM) which is mounted on a bracket, just forward of the center console. The impact sensor is an accelerometer that senses deceleration. The deceleration pulses are sent to a microprocessor which contains a decision algorithm. When an impact is severe enough to require airbag protection, the ACM micro processor sends a signal that completes the electrical circuit to the driver and passenger airbags. The sensor is calibrated for the specific vehicle and reacts to the severity and direction of the impact.

CLOCKSPRING

Clockspring-Typical:

The clockspring is snapped into a plastic mounting platform on the steering column behind the steering wheel. The clockspring is used to maintain a continuous electrical circuit between the wiring harness and the driver's airbag module.

This assembly consists of a flat ribbon like electrically conductive tape which winds and unwinds with the steering wheel rotation.

DRIVER AND PASSENGER AIRBAG MODULES
The Driver Airbag Module is located in the center of the steering wheel. The Passenger Airbag Module is located in the instrument panel above the glove box.

The Driver Airbag Module cover contains the horn switch, inflator device, and a fabric bag. The airbag cover/horn switch is serviced separately from the inflator and bag components. Refer to Horns for proper service procedure for horn switch. The Passenger Airbag Module is serviced as an assembly.

WHEN THE AIRBAG SYSTEM IS DEPLOYED BECAUSE OF A COLLISION, THE FOLLOWING MUST BE REPLACED:
- COMPLETE STEERING COLUMN ASSEMBLY
- LOWER STEERING COUPLER
- STEERING WHEEL
- STEERING COLUMN CLOCKSPRING
- DRIVER AIRBAG COVER/HORN SWITCH
- DRIVER AIRBAG MODULE PASSENGER AIRBAG MODULE
- UPPER INSTRUMENT PANEL WITH PAD