In a VVT system (Variable Valve Timing) the camshafts are driven by hydraulic actuators that are fed by the operating oil system of the engine through solenoids. This is managed by the PCM (Powertrain Control Module).
If the PCM observes that the camshaft movement on bank number 2 is not within the vehicle specifications or that the camshaft has not operated when commanded, the DTC P0028 OBDII code is set.