Body Control Module: Description and Operation
Part 1 of 3
Six-Step Troubleshooting Procedure
Diagnosis of the body system is done in six basic steps:
verification of complaint
verification of any related symptoms
repair of isolated problem
verification of proper operation
SYSTEM DESCRIPTION AND FUNCTIONAL OPERATION
The body system on the Prowler consists of a combination of modules that communicate over the CCD bus (Chrysler Collision Detection
multiplex system). All of the information about the functioning of all the systems is organized, controlled, and communicated by the CCD bus,
which is described in CCD Bus of the general information.
Through the CCD bus, information about the operation of vehicle components and circuits is relayed quickly to the appropriate module(s). All
modules receive all the information transmitted on the bus even though a module may not require all information to perform it's function. It will
only respond to messages "addressed" to it through a binary coding process. This method of data transmission significantly reduces the complexity
of the wiring in the vehicle and the size of wiring harnesses.
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. In 1997 the pressure in the canister is monitored by a
pressure switch. If the pressure drops below the minimum pressure limit, the ACM will turn ON the airbag warning lamp and set a diagnostic
trouble code (DTC).
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
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 has two different voltage supply circuits. They are supplied through fuse #5 and fuse #9.
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 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.
Passenger Airbag ON/OFF Switch