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.

The airbag control module (ACM) is an electronic module that monitors the airbag system for proper operation, stores diagnostic trouble code (DTCs), controls the airbag warning lamp, and contains the safing sensor and accelerometer that is responsible for airbag deployment. The ACM is located on the floor pan between the gear shifter and the parking brake assembly. The ACM provides diagnostic information (DTCs) to the technician through the DRB Ill via the CCD bus. Some circuits are tested continuously; others are checked only under certain circumstances. The warning lamp is hardwired to the ACM and there are no external impact sensors.

The AIRBAG warning lamp is the only point at which "symptoms" of a system malfunction can be observed by the customer. Whenever the ignition key is turned to the "run" or "start" position, the airbag control module performs a lamp check by turning the AIRBAG warning lamp on for 6-8 seconds and 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. If the lamp remains on, there could be an active fault in the system or the wire that operates the lamp may be 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.

Perform the WARNING LAMP CIRCUIT OPEN/SHORTED procedure to find the cause of any customer complaint regarding the AIRBAG warning lamp: 11A Repairing Warning Lamps Circuit Open/Shorted

- Warning lamp does not illuminate
- Warning lamp stays illuminated

The deceleration or g-force resulting from the impact of a front-end collision causes the electronic sensor inside the ACM to be triggered. This causes the inflates to be actuated thus deploying the airbags. The total time between triggering to full deployment and deflation of the bag is usually 1/10 of a second.

WARNING! The airbag control module contains the impact sensor, which enables the system to deploy the airbag. 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.

CCD Bus
The CCD (Chrysler Collision Detection multiplex system) bus is the means (A communicating between the Airbag Control Module (ACM) and the DRB about the operation of airbag system components and circuits.

The Chrysler Collision Detection multiplex system (CCD bus) consists of a twisted pair of wires. These wires run from the airbag control module (ACM) to the data link connector and the DRB. They receive and deliver coded information between the ACM and the DRB.

The two wires (D1 and D2) of the twisted pair that make up the COD multiplex system are called "bus+" (bus plus) and "bus-" (bus minus) respectively. Each wire has a measurable voltage level of roughly 2.5 volts, which is supplied by the DRB. In order to maintain the 2.5 volts on each line and provide a means of transportation for the coded messages, there is a "voltage divider network." This network, contained in the DRB, supplies bias and termination. Bias is the part of the voltage divider network that places both bus+ and bus- at 2.5 volts. Termination in the circuitry is required to complete the voltage divider network and also to provide some electromagnetic protection for the bus.

Airbag Control Module Location:

Airbag Control Module
The Airbag Control Module (ACM) contains the safing sensor and energy reserve capacitor. The safing sensor is located inside the ACM. The module is mounted on the tunnel/floor pan between the gear shift lever and the park brake lever. The safing sensor provides confirmation of a crash, but does not discriminate severity. The ACM monitors the system to determine the system readiness. The ACM contains on-board diagnostics, and will illuminate the AIRBAG warning lamp in the cluster when a fault occurs. The warning equipment is tested for 6 to 8 Seconds every time the vehicle is started.

Clockspring
The clockspring is mounted to 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
- Speed control switches
- Horn switch

The clockspring consists of a flat, ribbon like, electrically conductive tape which winds and unwinds with the steering wheel rotation.

Driver And Passenger Airbag Module

WARNING: NEVER DISASSEMBLE THE DRIVER OR PASSENGER AIRBAG MODULE, THERE ARE NO SERVICEABLE PARTS WITH IN THE MODULES.

Driver Airbag:

The Driver Airbag Module located on the steering wheel is the most visible part of the system. The airbag module contains a housing to which the cushion, inflator and cover are attached to.

The driver side inflator assembly is mounted from the back of the module housing. When supplied with the proper electrical signal the inflator assembly will produce a gas and discharge it directly into the cushion. A protective cover is fitted to the front of the Driver Airbag Module and forms a decorative cover in the center of the steering wheel. The Driver Airbag Module is mounted directly to the steering wheel.

Passengers Airbag:

The Passenger Airbag Module is located beneath the decorative cover of the instrument panel, facing the passenger seat.

The passenger inflator assembly is within the module housing. The module is mounted to the instrument panel retainer and support structure. When supplied with the proper electrical signal the inflator will produce a gas and discharge it directly into the cushion. A protective cover is fitted into the instrument panel over the airbag module and forms a decorative cover.