Airbag, obviously, and the manufacturer will require a new computer module, external sensors, and clock spring.
Except for damaged items, manufacturers are worried about liability issues if another serious crash occurs. The external sensors MIGHT work next time but there could be a tiny arced spot on the contacts that prevent proper operation. The reason for replacing the control module is it also contains a crash sensor. This "safing" sensor in the module AND one of the two external sensors must trip at exactly the same time for the bag to pop. Toyota used to advertise that THEIR airbag sensor terminals and contacts were gold-plated. Truth is, every manufacturer uses gold-plated crash sensors.
The computer sends a voltage up the "squib" or initiator wire to the airbag module. A sliding contact such as was used for horn buttons for many decades is not reliable enough for this system. There could be a tiny spot of dirt or corrosion that interrupts a solid contact during the exact microsecond the pulse of current must flow to the airbag. To solve that problem, all vehicles use a "clock spring" which is a wound-up ribbon cable under the steering wheel. The cable itself is not damaged during bag deployment, but the connector on the end of the pigtail wire often melts from the heat of the bag popping. The air that fills the bag comes from rapidly burning a pellet of rocket fuel, sodium azide. That heat is what does the damage to the connector and is why the clock spring should be replaced.
If the connector is not damaged, you might try to reuse the clock spring to save some money. Whenever the ignition switch is on, the computer sends a very small current through the ignitor in the airbag assembly, and through the external sensors to constantly test the wiring. If there is a break in the clock spring's ribbon cable, the system will be deactivated and the red warning light will turn on. When the red light is on, the airbag will not deploy in a crash, but it should be noted that a break in the ribbon cable or the squib wire creates an open circuit that leaves the ignitor susceptible to stray static electricity. I've never heard of an air bag accidentally deploying on an owner, but I have seen a ribbon cable unravel and peek out from under the base of a steering wheel, (in a Dakota), and there was a service bulletin referring to static electricity buildup from sliding your butt across the seat fabric on full-size trucks. To demonstrate an actual airbag deployment, it only takes some long wires and a 9 volt transistor battery to pop it. Static electricity that you can feel, or see the spark when you touch a door knob, is at least 3000 volts, so it could easily cause a bag to pop. By the way, the owner of that Dakota with the unraveling clock spring had ignored the "Airbag" light and inoperative horn for over two years. He had plenty of warning there was a problem long before static electricity became a concern.
Related to the static electricity issue, ALL connectors in the squib circuit will be bright yellow to identify them, and they will have shorting bars that short the two wires together when the connector is unplugged. In this way, any static voltage is applied equally to both wires in the squib. It takes a DIFFERENCE in voltage between the two wires to do electrical work. As long as components are disconnected at the connectors, static electricity is not a concern. Cutting wires renders the shorting bars ineffective; that's where accidental deployment could occur.
The other way clock springs go bad is the ribbon cables just break from repeated flexing. They also can not tolerate turning the steering wheel when the steering linkage is not connected. The steering system must also be centered, (straight ahead) when installing a new clock spring because they are designed to be able to rotate just a little more than the range of the steering system. Turning too much one way will wind the ribbon cable up so tight, it tears loose. Turning too far the other way will cause the cable to unwind as far as possible, then flip over on itself. After a few times, the cable will crack. An easy way to diagnose a defective clock spring is if the horn and cruise control don't work either because they both have circuits in the ribbon cable that go to the buttons on the steering wheel.
New clock springs have a paper tape across the hole where the steering shaft comes through that warns you to have the tires straight ahead when you install it. Also, there are little buttons on it that lock it in place preventing it from being turned. These buttons unlock when they're pushed down by the steering wheel when it's installed. If you search for a clock spring in a salvage yard, look for a vehicle that still has the steering linkage intact, then put the tires straight ahead before removing the steering wheel and clock spring. It too will lock in position when the steering wheel is pulled off. If you do not have cruise control, you can use any clock spring from a similar vehicle. If you do have cruise control, you must use a clock spring from a vehicle that had cruise control because you need the extra two wires in the ribbon cable. There are a lot of different clock spring part numbers for a given application so don't be surprised if the one you find is different even though it came from the same model truck. I would not look in other vehicle models because some clock springs have different mounting tabs, different connectors, and on some, the squib wire plugs into the clock spring housing, and on some, the wire comes out of the housing and must be threaded down the steering column and plugged in under the dash.
When replacing external crash sensors, it is critical that they be mounted in their proper positions and angles. Tipping them will change the speed at which they trip. If the trip speed is too high, you could be injured in a severe crash; too low, and not only would you likely waste a lot of money by popping an airbag unnecessarily, you could loose control of the vehicle in a minor crash and do more damage. Airbags in the steering wheel are only effective during head-on crashes. Likewise, external crash sensors are designed to trip during straight-on impact, give or take about 20 degrees. Turning a sensor could allow it to trip during a side impact, again popping the airbag when it won't do any good.
It is also important to mount the airbag computer in its original location or mounting bracket to prevent it from tripping at the wrong time. When you're done, watch the red warning light when you turn on the ignition switch. It should turn on for seven seconds during a self-test, then go out. If it comes back on, the computer detected a problem and memorized a diagnostic fault code. Most older aftermarket scanners can't access airbag systems so you'll need the Chrysler DRB3 to read the code. Some newer aftermarket scanners CAN access airbag systems. I have both the Chrysler DRB2 and DRB3. Manufacturer's scanners always do more things than aftermarket scanners, although the aftermarket stuff is getting better every year.
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Saturday, August 8th, 2009 AT 12:25 AM