Normal Operation
WARNING: This page is about a different car, the 2007 Lincoln Mark LT and 2007 Ford Pickup. However, it is still accessible from the selected car via links, so may be relevant.
The restraints control module (RCM) monitors the resistance between the ground connections of the case mounting and the reference ground at C310a pin 16, circuit 1203 (BK/LB).
If the RCM detects a difference in resistance, it will store diagnostic trouble code (DTC) B1921 in memory and flash lamp fault code (LFC) 14 (or higher priority code if one exists) on the air bag indicator.