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Old 07-08-2005, 05:44 PM
Sighted
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Need Technical help, airbag light and sensor question

92 SVX, 75,000 miles, ready to replace airbag but I have a few questions. Talked to my Subaru dealer about my situation and they gave me the standard "canned" answers, so I am asking the experts.
Car sustained minor damage that set off the airbag, damage was right (passenger) front fender, marks on bumper, slight "bow" in the hood all of which has been taken care of beautifully because the damage was so minor, I have an airbag I put in the vehicle but as yet am not brave enough to plug it back in. Subaru dealer says replace all sensors (2) but thats easy for them to recommend at $390 each plus shipping, everyone in the know agrees that the computer (srs airbag computer) is okay, Subaru says they don't know if I can test the circuit to determine if the sensors are bad so just replace them, I don't have deep pockets, am an excellent mechanic with a strong electrical background ( Master Electrician) and all the tools I could ever need so I know I am more than capable of fixing the problem if given good info so here I am with some specific questions:

1. If I test the airbag wires at the steering column and no voltage is present does that mean the sensors are good and it is safe to plug in the airbag and expect it not to fire in my face? or in another way does voltage set off the airbag or an open circuit set it off?

2. If I pull codes on the car right now will it tell me if I have a bad sensor or two or will it just show an airbag general problem?

3. What if I just eliminate the sensor from the system, would that show up as a trouble code?

Thanks for any assistance you may provide....
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Old 07-09-2005, 06:26 AM
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Every SRS system is unique and one should strictly adhere to the OEM's workshop manual. However, there are some 'standardized' rules that normally apply to all systems/makes: when an accident has ocurred that fires a bag, the sensor HAS to be replaced and the SRS computer HAS to be replaced, along with the deployed device (air bag, curtain, belt retractor, etc. - as is applicable.) Many SRS modules have sensors built inside of them, that is the first and main reason for their required replacement. Secondly, most OEMs feel that the reliability of the module could be suspect when the module is called upon again in a future accident.

Testing for voltage at the air bag connector doesn't necessarily indicate anything, many systems/devices use shorting pins, etc. What if the module depended on being able to detect continuity? If you have an open, or at least if the module thinks you have an open, it may consider it to be an accident related event and send firing voltage to the device. Again, you HAVE to use the OEM's workshop manual for the specific year and model. Not only is the current device at risk for being deployed unecessarily but it is also a matter of whether or not the device will be reliable, if it is ever needed again in the future.
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Old 07-09-2005, 08:32 AM
red95svx
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I agree with Beav. Even though you were only hit on the right side, it is very possible that your left sensor was activated by the sudden decelleration. The sensors can only activate once, and then must be replaced. Same for the SRS computer. If memory serves me right it has an onboard G sensor that can only go off once. Besides this is your safety we're taking about! Yes it is expensive, but I'd rather hit an airbag than a steering wheel! The next time you get into an accident (which hopefully will not happen) you'll be glad you spent the money and can walk away......



As far as the airbag going off during replacement: this is very, very rare, esp. if all suspect components have been replaced. Disconnect the battery and wait a half hour or so before doing anything (the SRS computer stores backup power to fire the airbags in case of power loss during the accident, but it doesn't last long). Check with the service manual for full details.

One thing to keep in mind: if your "Airbag" light comes on, the system goes into safe mode and completely shuts down. It WILL NOT fire airbags in an accident if that light is on. So no matter what you chose to do, make sure the light does not turn on after it's initial diagnostic check!! And yes, removing a sensor will cause a code and the light will come on.


Dave

Last edited by red95svx; 07-09-2005 at 08:39 AM.
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Old 07-09-2005, 09:48 AM
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Quote:
Originally Posted by red95svx
Even though you were only hit on the right side, it is very possible that your left sensor was activated by the sudden deceleration.
Or maybe just partially moved from rest, that may preclude it from working properly if needed in the future or even cause it to fire unintentionally.


Quote:
Originally Posted by red95svx
Disconnect the battery and wait a half hour or so before doing anything (the SRS computer stores backup power to fire the airbags in case of power loss during the accident, but it doesn't last long). Check with the service manual for full details.
Usually 30 seconds or so is all that is necessary as the back-up power is short-lived. The logic is that an accident only takes so long to occur and if power is lost during the accident back-up power should only be needed for a few seconds for secondary hits. After that they want it powered down in case occupant removal, etc. requires force applied that could cause a late firing.

Normally I give them a few minutes to bleed down.

Another point re: testing. There are 'dummy loads' that are used in place of pyro devices when testing that 'fool' the module into thinking that everything is in place and connected. These dummy loads are vehicle/system specific and are generally available only at dealerships. They are available to aftermarket but not many shops have them due to the quantity of different applications.

Quote:
Originally Posted by red95svx
One thing to keep in mind: if your "Airbag" light comes on(after the initial six second or so system check when the ignition is first turned on) , the system goes into safe mode and completely shuts down. It WILL NOT fire airbags in an accident if that light is on. So no matter what you chose to do, make sure the light does not turn on after it's initial diagnostic check!!(the initial six second or so system check when the ignition is first turned on) And yes, removing a sensor will cause a code and the light will come on.
(edited for clarity)
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