Airbag system — general information and precautions
General information
1. All models are equipped with two front airbags, formally known as the Supplemental Inflatable Restraint (SIR) system. This system is designed to protect the driver and the front seat passenger from serious injury in the event of a frontal collision. It consists of an array of external and internal (inside the SDM) information sensors (decelerometers), the Inflatable Restraint Sensing and Diagnostic Module (SDM), the inflator modules (a driver’s airbag in the steering wheel and a passenger’s airbag in the dash) and the wiring and connectors tying all these components together. Optional side-impact airbags, also known as roof rail or side curtain airbags, are available for protection against side impacts. The side-impact airbags, if equipped, are located along the left and right edges of the headliner, above the doors.
Airbag/inflator modules
Driver’s airbag/inflator module
2. The airbag inflator module in the steering wheel consists of a housing, the cushion (airbag), an initiating device and a canister of gas-generating material. The initiator is part of the inflator module deployment loop. When a collision occurs, the SDM sends current through the deployment loop to the initiator. Current passing through the initiator ignites the material in the canister, producing a rapidly expanding gas, which inflates the airbag almost instantaneously. Seconds after the airbag inflates, it deflates almost as quickly through airbag vent holes and/or the airbag fabric.
3. When the SDM sends current to the initiator, it travels through the airbag circuit to the steering column. From there, a clock-spring on the steering wheel delivers the current to the module initiator. This clock spring assembly, which is the final segment of the airbag ignition circuit, functions as the bridge between the end of the airbag circuit on the (fixed) steering column and the beginning of the circuit on the (rotating) steering wheel. It’s designed to maintain a closed circuit between the steering column and the steering wheel regardless of the position of the steering wheel. For this reason, removing and installing the clock spring is critical to the performance of the driver’s side airbag. For information on how to remove and install the driver’s side airbag, refer to Suspension and steering.
Passenger’s airbag/inflator module
4. The passenger’s airbag/inflator module is mounted above the glove compartment. It’s similar in design to the driver’s airbag except that it doesn’t use a clock spring. When deployed by the SDM, the passenger’s airbag bursts through the dashboard above the glove box. Although this area looks like it’s simply part of the dashboard, it’s actually a trim cover with a perforated seam that allows the cover to separate from the dash when the passenger’s airbag inflates (see illustrations).
26.4a Passenger airbag connector location (behind the glove box area)
26.4b Passenger airbag module location (glove box has been removed for clarity)
Side impact airbag/inflator (roof rail) modules
5. The (optional) side-impact airbag/inflator (roof rail) modules are mounted along the outer edges of the headliner, right above the door openings. They extend from the A-pillar (front windshield pillar) to the C-pillar (rear window pillar). Each module consists of a housing, an inflatable airbag, an initiator and a canister of gas-generating material. Each roof rail module employs its own side impact sensor (SIS), which contains a sensing device that monitors changes in vehicle acceleration and velocity. This data is sent to the SDM, which compares it with its program. When the data exceeds a certain threshold, the SDM determines that the vehicle has been hit hard enough on one side or the other to warrant deployment of the roof rail on that side. The SDM doesn’t deploy the roof rail airbags on both sides, just on the side being hit. Then the SDM sends current to the roof rail initiator to inflate the airbag, ripping open the headliner trim as it deploys to protect the occupant(s) on the left or right side of the vehicle. Side impact airbag/inflator modules are long enough to protect the driver and a left-side rear-seat passenger, or a front seat passenger and right-side rear-seat passenger.
Inflatable Restraint Sensing and Diagnostic Module (SDM)
6. The SDM is the computer module that controls the airbag system. Besides a microprocessor, the SDM also includes an array of sensors. Some of them are inside the SDM itself. Other external sensors are located throughout the vehicle. All of the sensors, internal and external, send a continuous voltage signal to the SDM, which compares this data to values stored in its memory. When these signals exceed a threshold value (when the SDM determines that the vehicle is decelerating more quickly than the threshold value), the SDM allows current to flow through the circuit to the appropriate airbag module(s), which initiates deployment of the airbag(s).
7. The SDM is located underneath the center console. Once the console is removed (see Center console and overhead console — removal and installation) the carpet padding will need to be removed. The easiest way is to cut around the SDM and remove that section of carpet padding rather than pulling the entire carpet padding up. Just reinstall the cut-out piece back into place when you’re finished (see illustration).
26.7 SDM location (seats and center console removed for clarity)
Disarming the system and other precautions
Warning: Failure to follow these precautions could result in accidental deployment of the airbag and personal injury.
8. Whenever working in the vicinity of the steering wheel, instrument panel or any of the other SIR system components, the system must be disarmed. To disarm the system:
a) Point the wheels straight ahead and turn the key to the Lock position.
b) Disconnect the cable from the negative battery terminal. Refer to Engine electrical systems for the disconnecting procedure.
c) Wait at least two minutes for the back-up power supply to be depleted
9. Whenever handling an airbag module, always keep the airbag opening (the trim side) pointed away from your body. Never place the airbag module on a bench or other surface with the airbag opening facing the surface. Always place the airbag module in a safe location with the airbag opening (the upholstered side) facing up.
10. Never measure the resistance of any SIR component or use any electrical test equipment on any of the wiring or components. An ohmmeter has a built-in battery supply that could accidentally deploy the airbag.
11. Never dispose of a live airbag/inflator module. Return it to a dealer service department or other qualified repair shop for safe deployment and disposal.
12. Never use electrical welding equipment in the vicinity of any airbag components. The connectors for the system are easy to spot because they’re bright yellow. Do NOT disconnect or tamper with these connectors, or you run the risk of setting a Diagnostic Trouble Code (DTC) in the SDM. Like the PCM, the SDM has a malfunction indicator light, known as the AIR BAG indicator light, on the instrument cluster. When you turn the ignition key to ON, the SDM checks out all of the system components and circuits. If everything is okay, the AIR BAG indicator light goes off, just like the PCM’s Malfunction Indicator Light (MIL). But if there’s a problem somewhere, the light stays on, and will remain on until the problem is repaired and the DTC(s) cleared from the SDM’s memory.
Impact seat belt retractors
13. All models are equipped with pyrotechnic (explosive) units in the front seat belt retracting mechanisms for both the lap and shoulder belts. During an impact that would trigger the airbag system, the airbag control unit also triggers the seat belt retractors. When the pyrotechnic charges go off, they accelerate the retractors to instantly take up any slack in the seat belt system to more fully prepare the driver and front seat passenger for impact.
14. The airbag system should be disabled any time work is done to or around the seats.
Warning: Never strike the pillars or floor pan with a hammer or use an impact-driver tool in these areas unless the system is disabled