The FICM is a two-circuit board unit. One board is a power supply and one board is a logic board. The logic board (left) holds all the programming and logic functions. It almost never fails. The power supply board is used to ramp up 12 volts DC to 48 volts DC, and that is what the logic board uses to actuate the fuel injectors. Since it often fails, the power supply is replaced with the Bullet Proof Diesel FICM kit. If this board does not fail completely, it will often put out only a fraction of the 48 volts it is supposed to, therefore leaving you with a poor-running truck.