System Overview
AIRBAG SYSTEMThe airbag system is designed to provide increased driver and passenger protection if the vehicle is involved in a front-end collision. The system is designed to be used in conjunction with the seat belt system. Currently, DaimlerChrysler Corporation uses two types of Airbag Control Modules (ACM).
Whenever the ignition key is turned to the "run" or "start" position, the airbag control module (ACM) performs a warning indicator check by turning the AIRBAG warning indicator on. The indicator stays lit for 6 to 8 seconds, then goes off. If the indicator remains off, it means the ACM has checked the system and found it to be free of discernable malfunctions.
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 DRBIII via the PCI bus.
The deceleration of g-forces 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 air bag is 1/10th of a second (100 ms).
2002 Jeep Wranglers (TJ) will be equipped with a passenger airbag ON/OFF switch. This switch has an ACM controlled LED that will light when the switch is in the "OFF" position.
Use the diagnostic tests to find the cause of any customer complaint regarding the AIRBAG warning indicator such as:
* Airbag warning indicator does not come on at all
* Airbag warning indicator stays on
Fig.1 SRS Logo:
A dual front airbag system is standard factory-installed safety equipment on this model. The airbag system is a passive, inflatable, Supplemental Restraint System (SRS) and vehicles with this equipment can be readily identified by the "SRS - AIRBAG" logo molded into the driver airbag trim cover in the center of the steering wheel and also into the passenger airbag door on the instrument panel above the glove box. Vehicles with the airbag system can also be identified by the airbag indicator,which will illuminate in the instrument cluster for about 7 seconds as a bulb test each time the ignition switch is turned to the ON position.
The ACM and the EMIC each contain a central processing unit and programming that allow them to communicate with each other using the Programmable Communications Interface (PCI) data bus network. This method of communication is used for control of the airbag indicator on all models. (Refer to ELECTRONIC CONTROL MODULES/COMMUNICATION - DESCRIPTION).
Hard wired circuitry connects the airbag system components to each other through the electrical system of the vehicle. These hard wired circuits are integral to several wire harnesses, which are routed throughout the vehicle and retained by many different methods. These circuits may be connected to each other, to the vehicle electrical system, and to the air- bag system components through the use of a combination of soldered splices, splice block connectors, and many different types of wire harness terminal connectors and insulators. Refer to the appropriate wiring information. The wiring information includes wiring diagrams, proper wire and connector repair procedures, further details on wire harness routing and retention, as well as pin-out and location views for the various wire harness connectors, splices and grounds.
The airbag system is referred to as a supplemental restraint system because it was designed and is intended to enhance the protection for the front seat occupants of the vehicle only when used in conjunction with the seat belts. It is referred to as a passive system because the vehicle occupants are not required to do anything to make it work. The primary passenger restraints in this or any other vehicle are the standard equipment factory-installed seat belts. Seat belts are referred to as an active restraint because the vehicle occupants are required to physically fasten and properly adjust these restraints in order to benefit from them. The vehicle occupants must be wearing their seat belts in order to obtain the maximum safety benefit from the factory-in- stalled airbag system.
The airbag system electrical circuits are continuously monitored and controlled by a microprocessor and software contained within the Airbag Control Module (ACM). An airbag indicator in the ElectroMechanical Instrument Cluster (EMIC) lights for about 7 seconds as a bulb test each time the ignition switch is turned to the ON or Start positions. Following the bulb test, the airbag indicator is turned ON or OFF by the ACM to indicate the status of the airbag system. If the airbag indicator comes on at any time other than during the bulb test, it indicates that there is a problem in the airbag system electrical circuits. Such a problem may cause the airbags not to deploy when required, or to deploy when not required.
The clockspring on the top of the steering column allows a continuous electrical circuit to be maintained between the stationary steering column and the driver airbag inflator, which rotates with the steering wheel. The passenger airbag ON/OFF switch allows the passenger side airbag to be disabled when circumstances necessitate that a child, or an adult with certain medical conditions be placed in the front passenger seating position. Refer to the owner's manual in the vehicle glove box for recommendations concerning the specific circumstances where the passenger airbag ON/OFF switch should be used to disable the passenger airbag.
Deployment of the airbags depends upon the angle and severity of the impact. The airbag system is designed to deploy upon a frontal impact within a thirty degree angle from either side of the vehicle center line. Deployment is not based upon vehicle speed; rather, deployment is based upon the rate of deceleration as measured by the forces of gravity (G force) upon the airbag system impact sensor, which is integral to the ACM. When a frontal impact is severe enough, the microprocessor in the ACM signals the inflator units of both airbag modules to deploy the airbags. During a frontal vehicle impact, the knee blockers work in concert with properly fastened and adjusted seat belts to restrain both the driver and the front seat passenger in the proper position for an airbag deployment. The knee blockers also absorb and distribute the crash energy from the driver and the front seat passenger to the structure of the instrument panel.
Typically the driver and front seat passenger recall more about the events preceding and following a collision than they have of the airbag deployment itself. This is because the airbag deployment and deflation occur so rapidly. In a typical 48 km/h (30 mph) barrier impact, from the moment of impact until both airbags are fully inflated takes about 40 milliseconds. Within 1 - 2 seconds from the moment of impact, both airbags are almost entirely deflated. The times cited for these events are approximations, which apply only to a barrier impact at the given speed. Actual times will vary somewhat, depending upon the vehicle speed, impact angle, severity of the impact, and the type of collision.
When the ACM monitors a problem in any of the airbag system circuits or components, it stores a fault code or Diagnostic Trouble Code (DTC) in its memory circuit and sends an electronic message to the EMIC to turn ON the airbag indicator. Proper testing of the airbag system components, the Programmable Communications Interface (PCI) data bus, the data bus message inputs to and outputs from the EMIC or the ACM, as well as the retrieval or erasure of a DTC from the ACM requires the use of a DRBIII scan tool. Refer to the appropriate diagnostic information.
See the owner's manual in the vehicle glove box for more information on the features, use and operation of all of the factory-installed passenger restraints, including the airbag system.