Did you read all the stuff at the link I provided before?? You need to check that out to understand how the ABS monitor works.
Anyway, here is some specific info on code 12:
Diagnostic Trouble Code 12 -- Low Battery Voltage
Normal Operation
The air bag diagnostic monitor measures the voltage at Pin 14 of the air bag diagnostic monitor connector. Voltage at Pin 14 should be equal to battery voltage. If the voltage at Pin 14 drops to less than 9 volts, the air bag diagnostic monitor will store in memory and flash out on the air bag indicator a DTC 12. Should the loss of battery voltage at Pin 14 be intermittent or repaired, the air bag diagnostic monitor will flash out a DTC 52 (or higher priority code if one exists) on the next ignition switch cycle.
Possible Causes
Low voltage at air bag diagnostic monitor Pin 14 can be caused by:
* An open in the battery circuit that would prevent battery voltage from reaching air bag diagnostic monitor Pin 14.
NOTE:
If a short to ground exists on any of the Circuits 607 (LB/O), 614 (GY/O), 615 (GY/W), or 616 (PK/BK) leading to a DTC 13 or 53, or similarly a short to ground exists on any of Circuits 617 (PK/O), 619 (PK/W), 624 (Y/W), 625 (Y/LG) leading to a DTC 14 or 54, the air bag diagnostic monitor will activate a solid state switch at Pin 13 of the air bag diagnostic monitor. This causes the 10 amp battery fuse to blow, thus disarming the air bag system and preventing inadvertent air bag deployment. If the 10 amp instrument panel (or power distribution in some vehicles) battery fuse has blown, it must be replaced by a 10A fuse.
WARNING:
UNDER NO CIRCUMSTANCES SUBSTITUTE ANOTHER FUSE VALUE. ANY FUSE OTHER THAN 10A MAY CAUSE DISARMING FAILURE AND MAY RESULT IN DANGER TO THE OCCUPANTS OF THE VEHICLE. DO NOT ATTEMPT TO REPLACE THE 10A FUSE UNLESS THE AIR BAG SYSTEM FIRST HAS BEEN DEACTIVATED (SEE DEACTIVATION PROCEDURE FOR DETAILS).
After the air bag diagnostic monitor has disarmed the air bag system, it will not be enabled to disarm again until the appropriate condition (DTC 13, 14, 53, or 54) has been serviced and cleared (see DTC «13» , «14» , «53» , and «54» and «Diagnostic Trouble Code Clearing procedure» descriptions for further details).
* A short to ground on the battery feed circuit between the fuse and Pin 13 or Pin 14 of the air bag diagnostic monitor.
* A concern in the charging system causing battery voltage to drop below 9 volts.
Rick
