SIR (air bag) New One on Me!!!

[MrCritical]

A lady brought an 3 year old GM J body car to the shop today with a strange situation.

She had bought the car used at a local new car dealer. She had found that there was no fuse in the fuse box for the SIR system but the SIR warning light was not on.

I look up the service info on GM's website, and it says the SIR light will come on and stay on if the fuse is removed. I hooked up a scan tool and there are no current or history fault codes.

I didn't take the steering wheel cover off, but a SIR tech who pushed on the horn button says he's 99% sure there's no air bag in there.

I know there are dummy sensors to fool the ECU/ECM into believing there are o2 sensors where there are non, but has anyone heard of this before on SIR?

 

[javacontour]

Why not just get the air-bag. If she bought this at a new car dealer as a used car it seems there may be some liability on their part.

I wonder if they simply removed the light from the instrument cluster?

 

[MrCritical]

That's what I thought at first too, java. But when you turn the key on it runs the bulb check.

 

[javacontour]

So maybe the tech is wrong and the bag is there.

Is it possible he has the wrong fuse location in the fuse box? If the bulb check is coming on, I'd think something is powered up.

I guess the only other thing to do is to see if the airbag is really there?

 

[Hootbro]

Something is not right here and my money is on a mistaken customer and/or mechanic.

The SIR on ignition startup sends voltage to the sensing and diagnostic module (SDM) which does a diagnostic check of the whole SIR circuit. The SDM during this diagnostic sends a data bus command to the instrument panel to flash the Air Bag light seven (7) times and extinguish when no faults are found.

If the airbag light is testing and not staying on, then the system is fine and the SDM is getting voltage.

I doubt the air bag is missing on the steering column but for what it is worth, Google "Air Bag Simulators" and you will see there is products to simulate airbags. These simulators are usually marketed to the crowd that likes to install Race type steering wheels that have no provisions for the factory air bag. These simulators (basically a glorified resistor)to still allow the SIR system work for the passenger air bag.

Attached is a schematic from a 2001 J body service manual I use for my Cavalier.

http://www.gunsnet.net/album/data//500/SIR_Schematic.jpg

 

[Matt_S]

I was gonna say someone jury-rigged the wiring to fool the computer, but I think Hootbro has it spot-on. Some unscrupulous used car salesman probably swapped the real bag out for a dummy unit, sold the real one and installed an air bag sim to make it look like everything's kosher.

What this woman should do is have it checked (air bags aren't hard to remove) and if that's really the case, she may have a legal case against the place she bought the car from (or maybe they'll choose to make things right).