Air Bag Systems: Description and Operation

AIRBAG SYSTEM
The airbag system is designed to proved 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. 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 is an electronically triggered system that used only its own internal electronic sensor to trigger the airbags. The JX Body used only the AECM system.

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 six to eight 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 deflation of the airbag is 1/10th of a second.

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 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 code(s).

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.

Always begin by reading the diagnostic trouble codes using the DRB III Then perform the specific test(s). If more than one code exists, diagnostic priority should be given to the active code(s).

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, diagnostic trouble codes are used as a diagnostic tool.

Active codes
An active trouble code indicates an ongoing malfunction. This means that the defect is currently there every time the airbag 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.

Stored codes
Airbag codes are automatically 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 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 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 stored codes and, with the ignition "on," wiggle the wire harness and connectors, rotating 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.

Airbag trouble codes
The airbag control module may report any of the following diagnostic trouble codes.

For these codes, replace the Airbag Control Module (ACM) even if set intermittently:
- AECM Accelerometer
- AECM Internal Diagnostic 1
- AECM Internal Diagnostic 2
- AECM Output Driver
- AECM Stored Energy

For these codes, refer to the appropriate diagnostic procedure:
- AECM & Cluster CCD Message Mismatch
- Driver Squib Circuit Open
- Driver Squib Circuit Shorted
- Driver Squib Term Shorted to Battery
- Driver Squib Term Shorted to Ground
- Loss of Ignition Run Only
- Loss of Ignition Run/Start
- No CCD Communication
- No Cluster CCD Bus Message
- Passenger Squib Circuit Open
- Passenger Squib Circuit Shorted
- Pass Squib Term Shorted to Battery
- Pass Squib Term Short to Ground
- Warning Lamp Circuit Open
- Warning Lamp Circuit Shorted
- Output Driver Not Tested