Wrangler 4WD L4-150 2.5L VIN P MFI (1998)
Body Control Module: Description and Operation
Airbag System
IDENTIFICATION OF SYSTEM
The vehicle systems that are part of the "body" system are:
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airbag system
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instrument cluster
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vehicle communications
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. Currently, Chrysler Corporation uses two types of airbags control modules (ACM).
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 uses only its own internal electronic sensor to trigger the airbags. The TJ Body uses 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 6 to 8 seconds, then goes off. If the lamp remains off, it means the ACM has checked the system and found it to
be free of discernable 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 via the CCD bus.
The AIRBAG warning lamp is the only point at which "symptoms" of a system malfunction can be observed by the customer. The seat belt warning lamp
is used as a back-up for a failed airbag warning lamp. If at "ignition on" (when the airbag warning lamp should be activated for 7 seconds), the airbag
lamp fails to come on for the 7 second bulb check, the seat belt warning lamp will flash on and off for 30 seconds after its 7 second bulb check and will
perform as the airbag warning lamp.
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.
Starting in 1998 some TJ's will be equipped with a passenger airbag disable switch (PADS). This switch has a led that will light when the switch is in the
"OFF" position. While in the "OFF" position a circuit board inside the switch will simulate a passenger airbag to prevent the ACM from loging a DTC.
However it is important that the ignition be in the "OFF" before moving the PADS to the "OFF" or "ON" position, otherwise the ACM may log a DTC
and turn on the airbag warning lamp due to the momentary open the switch contacts.
Use the test procedures to find the cause of any customer complaint regarding the AIRBAG warning lamp such as:
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warning lamp does not come on at all
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warning lamp stays on
Airbag Diagnostic Trouble Codes
Airbag diagnostic trouble codes consist of active and stored codes. If more than one 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
to diagnose an individual code.
Always begin by reading the diagnostic trouble codes using the DRB. This procedure begins with AIRBAG TEST 1A - Identifying Airbag System
Problems. This will direct you to the specific test(s) that must be performed. 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
