The generator field circuit has a built-in coil, which is in charge of maintaining the battery with optimum charge levels. So, when the vehicle is in motion, the Powertrain Control Module (PCM) will monitor alternator/generator voltages and continuity levels.
The P0626 OBDII diagnostic code is a generic code that is set when the PCM detects signal voltages, which are at their highest levels regarding the generator field coil circuit.
The “F” is simply a continuous representation of the error, which indicates that the generator circuit is malfunctioning.