On vehicles using the VVT system (Variable Valve Timing), the camshaft position is controlled by the vehicle computer. This is accomplished through the regulation of the engine oil using a control solenoid.
The control solenoid is commanded by a pulse width modulated signal from the PCM (Powertrain Control Module). This signal is monitored by the PCM itself and if it detects that the voltage is below the limits already set, the Check Engine light will illuminate along with the DTC P0076 OBDII code.