Air Bag Code 12 Assistance

[ZeroDCX]

So two days ago, during morning traffic, I caught a faint burning smell. I thought it was just my imagination, but my air bag light immediately came on and it began flashing code 12. In the interior fuse box, fuse 4 was burned. I replaced it with another fuse and whenever I turn the ignition on, it just proceeds to burn another fuse. I know of the air bag reset procedure, which doesn't apply to code 12. But does anyone know where to start diagnosing this issue? (Praying my airbag is still functional).

I did my research and came up with this site: Mustang 1995 Air Bag Diagnostic Codes

But it doesn't really help me with code 12 other than to note that I possibly have a short leading to code 12 or the system is purposely burning out the fuse to ensure the air bag is not deployed (solid state switch).

I have not attempted to remove power from the car. As I would rather attempt to figure out what's going on rather than make it go away. Also I've searched for threads pertaining to this issue just to come up with some wires around the clutch/brake pedals that get their shielding rubbed off of them leading to a possible short. I peeked underneath to find no such occurrence. My horn and cruise control still work, which leads me away from the clockspring (correct me if I'm wrong). Any one else have and figured out a similar issue or have testing procedure for the air bag system?

 

[Rick98Z]

Interested to see what fix is, my 96 had airbag light on when I purchased it 2 weeks ago and it also just keeps blowing fuses when I replace them...

 

[ZeroDCX]

Update: I finally had the time to actually test the system for shorts and ended up having none. I pulled my Air Bag Diagnostic Module to find a blown Metal Oxide Varistor.

 

[Rick98Z]

Do you have to take the module apart to find problem?

 

[ZeroDCX]

I removed the affected MOV (Metal Oxide Varistor), since all is does is clamp voltage/protect other component from electrical surge, and plugged the module back in, replaced the fuse (#4 - 10A), turned on the ignition and it read out Code 52 (Intermittent or Repaired Lost Battery Feed). Which can be cleared by using the diagnostic connector at the base of the glove box. I'm going to replace the MOV and then report back afterwards. But all seems well thus far.

Threads with similar issues:
http://www.lincolnsonline.com/forum/showthread.php?t=81295
http://www.ford-trucks.com/forums/602583-airbag-diagnostic-control-module.html?styleid=22

Do you have to take the module apart to find problem?

Yes sir. I will post pics shortly. It's not a difficult task, you can access the bolts and remove the module just by pulling back some of the carpeting.


Note: The MOV marked MOV40 is the affected one.

 

[Rick98Z]

Great info and pics, I will def need to check mine out!

 

[Rick98Z]

So is there any easy way to get module out?

 

[Rick98Z]

Zero I got mine out, were you able to seperate circuit board from metal mounting bracket? It seems like an 2 odd torx screws that require a special bit to disassemble???

 

[ZeroDCX]

It is held by two T20 security torx bit screws.

http://www.veryuseful.com/mustang/tech/airBag/airBag95.html

This website can provide more assistance than I can concerning the air bag system. I followed Code 13's troubleshooting steps and came to the my conclusion that it had to be the Air Bag Diagnostic Module.


Edit: For those of you wondering which pins are which. I used this as a guide since I could not locate pinout numbering for our 95+ cars.

Note: Pay no attention to the actual schematic, but look at the pinout numbering on the bottom of the page and compare to the 95+ schematic.
http://www.veryuseful.com/mustang/tech/airBag/images/airBagSchem1991.jpg

 

[Rick98Z]

I know it sounds stupid but where do you find bits for security torx bits...all my sets have standard torx bits?

Ha google does amazing things, I guess a lot of places carry them...looks like time for another trip to the store lol!

My MOV40 was definitely the affected one just as yours, thanks for all the help!

 

[ZeroDCX]

I know it sounds stupid but where do you find bits for security torx bits...all my sets have standard torx bits?

Ha google does amazing things, I guess a lot of places carry them...looks like time for another trip to the store lol!

My MOV40 was definitely the affected one just as yours, thanks for all the help!

I actually purchased my set at an Autozone, but I'm sure you can get them cheap from Harbor Freight or something of the sort. Any auto part store should carry them.

No prob.





If you're absolutely (and I mean absolutely) sure of this, then you can remove the affected Metal Oxide Varistor (MOV40). Attach it back to the car (it must be in mounting position since its mounts are used as a grounding source), replace Fuse 4 (10A) underneath the dash and turn the ignition on (don't start the car). The MOV protects other components within the module from damage due to voltage spikes by clamping voltage and acting as a sacrificial fuse in the event of such an occurrence, so the module's components that are supposed to be protected by MOV40 will not be protected from voltage spikes (hence why I say not to start the car). If it flashes with Code 52 then you've found your problem. But I would replace the varistor if I were you, better safe than sorry. Code 52 can be cleared by using the diagnostic connector underneath the glove box area. Good luck.

Edit: Even-though this should not be an issue since the airbags are actually hardwired to the front impact sensors. If you wish to play it safe, you could always disconnect the airbags first before attempting this. But then it would also display different codes for the airbags (Code 32/33). Just as long as it doesn't read out Code 12/13 and blow the number four fuse you should be good to go assuming you had the same issue I did.

 

[Rick98Z]

Do you know which varistor to replace it with? I see about a bazillion options when searching electronics sites lol???

 

[ZeroDCX]

That is where the problem lies. I could not track down the proper varistor by cross-referencing the part numbers of the old unit. So you could either replace it from a known good working unit, by pulling one from a vehicle at the local junkyard or replace it with a comparable unit "Littelfuse V18ZA40P", but this isn't verified.

Concerning the used unit, MOV40 and MOV60 are identical varistors and should be able to be interchanged. So if you were to pull one from a used unit, you would be able to retrieve either varistor and be within stock specifications.

 

[ZeroDCX]

Update: I replaced the varistor and cleared Code 52 with the diagnostic connector. Now I the air bag indicator operates as it should. No more air bag light glaring at me.

 

[Rick98Z]

Good job, what varistor did you end up using?

 

[ZeroDCX]

Replaced it with a known good unit from another working module.