See Figure 1
The Supplemental Restraint System (SRS) is designed to work in concert with the seat belts to further prevent personal injury during a head-on collision with another object. The SRS utilizes an air bag module, front impact sensors, a clockspring, low pressure switch and a diagnostic module.
With the battery cables connected, the SRS system is energized and monitoring the front impact sensors and the safing sensor for collision confirmation messages. When the vehicle strikes, or is struck by, another object (such as a tree, wall, another vehicle, etc.), the front impact sensors and safing sensor send impulses to the diagnostic module, which determines the force and direction of the impact. Based on this information the diagnostic module either deploys or does not deploy the air bag.
The only time that the SRS is completely disarmed with no chance of accidental deployment is when the battery cables have been disconnected from the battery and set aside, and at least 2 minutes have gone by to allow the system capacitor to discharge any residual energy.
Air Bag Control Module (ACM)
The Air Bag Control Module (ACM) is one of the most visible part of the system. It contains the air bag safing sensor and energy reserve capacitor. The ACM is mounted on the tunnel floor pan forward of the center console. The safing sensor is located inside the ACM. The safing sensor provides confirmation of a crash, but does not determine the severity. The ACM monitors the system to determine the system readiness. The ACM will store a sufficient energy to deploy the airbags for only two minutes after the battery has been disconnected. The ACM contains on-board diagnostics, and will illuminate the AIRBAG warning lamp on the dash when a fault has occurred. The warning equipment is tested for a few seconds every time the vehicle is started.Front Impact Sensors
The driver and passenger air bag system is a safety device designed to reduce the risk of fatality or serious injury, caused by a frontal impact of the vehicle.
The two front impact sensors provide verification of the direction and severity of the impact. Three impact sensors are used. One is called a safing sensor. It is located inside the diagnostic module which is mounted on the floor pan, just forward of the center console. The other two sensors are mounted on the upper crossmember of the radiator closure panel on the left and right side of the vehicle under the hood.
The impact sensors are threshold sensitive switches that complete an electrical circuit when an impact provides a sufficient G force to close the switch. The sensors are calibrated for the specific vehicle and react to the severity and direction of the impact.Clockspring
The clockspring is mounted on the steering column behind the steering wheel and is used to maintain a continuous electrical circuit between the wiring harness and the driver's air bag module. This assembly consists of a flat ribbon-like electrically conductive tape which winds and unwinds with the steering wheel rotation.Air Bag Module
See Figure 2
The drivers air bag module is located on the steering wheel and is the most visible part of the system. It contains the air bag cushion and its supporting components. The module contains a housing to which the cushion and inflator are attached and sealed.
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 air bag module and form a decorative cover in the center of the steering wheel. The driver air bag module is mounted directly to the steering wheel.PASSENGERS SIDE
The passenger air bag module is located beneath the decorative cover of the instrument panel, facing the passenger seat. The passenger inflator is within the module housing. The module is mounted to the upper and lower instrument panel. 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 way passenger air bag module. This cover will pivot out of the way and allow the cushion to fully inflate.Low Pressure Switch
The passenger air bag module has a low pressure switch attached to it. The purpose of a pressure switch is to monitor the compressed gas pressure in the inflator. If the gas pressure falls below specifications, the pressure switch will illuminate the air bag lamp in the dash. If this situation occurs, it will be necessary to replace the passenger side air bag module.
When working on the SRS or any components which require the removal of the air bag, adhere to all of these precautions to minimize the risks of personal injury or component damage:
Handling A Live Air Bag Module
At no time should any source of electricity be permitted near the inflator on the back of the module. When carrying a live module, the trim cover should be pointed away from the body to minimize injury in the event of accidental deployment. In addition, if the module is placed on a bench or other surface, the plastic trim cover should be face up to minimize movement in case of accidental deployment.
When handling a steering column with an air bag module attached, never place the column on the floor or other surface with the steering wheel or module face down.Handling A Deployed Air Bag Module
The vehicle interior may contain a very small amount of sodium hydroxide powder, a by-product of air bag deployment. Since this powder can irritate the skin, eyes, nose or throat, be sure to wear safety glasses, rubber gloves and long sleeves during cleanup.
If you find that the cleanup is irritating your skin, run cool water over the affected area. Also, if you experience nasal or throat irritation, exit the vehicle for fresh air until the irritation ceases. If irritation continues, see a physician.Begin the cleanup by putting tape over the two air bag exhaust vents so that no additional powder will find its way into the vehicle interior. Then remove the air bag and air bag module from the vehicle.
Use a vacuum cleaner to remove any residual powder from the vehicle interior. Work from the outside in so that you avoid kneeling or sitting in an uncleaned area.Be sure to vacuum the heater and A/C outlets as well. In fact it's a good idea to run the blower on low and to vacuum up any powder expelled from the plenum. You may need to vacuum the interior of the car a second time to recover all of the powder.Check with the local authorities before disposing of the deployed bag and module in your trash.
After an air bag has been deployed, the air bag module and clockspring must be replaced because they cannot be reused. Other air bag system components should be replaced with new ones if damaged.
DISARMING THE SYSTEM
- Disconnect the negative battery cable and isolate the cable using an appropriate insulator (wrap with quality electrical tape).
- Allow the system capacitor to discharge for 2 minutes before starting any repair on any air bag system or related components. This will disable the air bag system.
ARMING THE SYSTEM
To arm the SRS, reconnect the negative battery cable. This will automatically enable the air bag system.