Note 13
WARNING: This page does not describe the selected car, but rather 9 other vehicles, including the 2005 Ford RV Cutaway, 2005 Ford Pickup, 2005 Ford F550 Super Duty, 2005 Ford F450 Super Duty, and 2005 Ford Excursion. However, it is still accessible from the selected car via links, so may be relevant.
This DTC will set if system voltage is greater than 18 volts or less than 10 volts during the KOER Glow Plug self-test. Refer to CHARGING SYSTEM - GENERAL PROCEDURES to diagnose the undercharging or overcharging condition.