I have a 1993 Ford Aerostar flashing an airbag code of 12. My son said it started when the car wouldn't start due to a weak battery and corrosion. My son for an unknown reason started pulling fuses to check for blown ones. When the fuses were replaced the airbag light began to blink while driving indicating a 12 code. Also on another note, when I turn the key to the "accsesory" position, back one click from off, there is a buzz which sounds about every second. The buzz goes away when key is in "on" or "start" position. I do not know if the airbag code and buzzing are related. The airbag light does not flash when key is in "accsesory" position.
Fault code no. 12 Loss Of Battery Power To Air Bag Firing Circuit
CODE 12, LOSS OF BATTERY POWER TO AIR BAG FIRING CIRCUIT
NOTE: Before proceeding, follow air bag service precautions. See SERVICE PRECAUTIONS. After servicing has been performed, recheck AIR BAG warning light for codes with Air Bag Simulator (105-00010) still in place of air bag module. If system checks okay, install air bag module and reactivate air bag system.
Diagnostic monitor measures voltage at terminal No. 13 of diagnostic monitor connector. Reading should be battery voltage. If voltage drops to less than 9 volts, Code 12 will set.
Code 12 may be caused by an open in circuit No. 37 or 38, an internal short to ground within safing sensor, a short to ground in circuit No. 611 or circuit No. 612, or a charging circuit problem.
VERIFY CONDITION - Turn ignition on. Check for fault codes. If Code 12 is flashing, go to step 2). If Code 12 is not flashing, check connectors, wiring, splices, crimps and charging circuit for an intermittent problem. DO NOT proceed with diagnostic test until code is flashing. Failure to do so will result in needless replacement of diagnostic monitor.
VOLTAGE CHECK - Deactivate air bag system. See COMPLETE SYSTEM DEACTIVATION under DISABLING & ACTIVATING AIR BAG SYSTEM. Disconnect diagnostic monitor. Diagnostic monitor is located on left side of steering column under instrument panel. Turn ignition on. Measure voltage between terminals No. 13 (Yellow wire on Aerostar or Black/Orange wire on Econoline) and No. 3 (Black wire) of diagnostic monitor Gray connector. See Fig. 15. If battery voltage is not present, go to step 3). If battery voltage is present, replace diagnostic monitor.
CHECK INSTRUMENT PANEL FUSE - On Aerostar, check fuse No. 10 in instrument panel fuse block. On Econoline, check fuse No. 15 in instrument panel fuse block. On all models, if fuse is blown, go to step 4). If fuse is okay, go to step 6).
CHECK FOR SHORT TO GROUND - Replace fuse. If fuse does not blow again, go to step 5). If fuse blows again, locate and repair short to ground between fuse and terminal No. 13 of diagnostic monitor. After repair is completed, go to step 6).
CHECK FOR SHORT TO GROUND IN CIRCUITS No. 611 & 612 - Turn ignition off. Reconnect diagnostic monitor. Turn ignition on. Recheck fuse No. 10 (Aerostar) or fuse No. 15 (Econoline). If fuse is blown, locate and repair short to ground in circuit No. 611 (White/Orange wire) or circuit No. 612 (Purple/Orange wire). If fuse is okay, short to ground is intermittent. Check all circuits between fuse and terminal No. 13 of diagnostic monitor. Also check circuits No. 611 and 612 for intermittent shorts. Repair as necessary and go to step 6).
VERIFY SYSTEM - Replace fuse if necessary. Reconnect all air bag system connectors. When repairs are complete, check AIR BAG warning light for codes with Air Bag Simulator (105-00010) still in place of air bag module. If system checks okay, reactivate air bag system.