To achieve the appropriate operation in the internal combustion engine, valves need to be opened or closed at different cycle points as needed. For example, the valves must be open to allow air and fuel to enter the cylinder during intake. On compression and power, the intake and exhaust valves should be closed. Besides, the valves open to allow exhaust through the intake manifold during exhaust.
To achieve the best results, modern engines are equipped with Variable Valve Timing (VVT). This system achieves on-demand performance and fuel economy. Depending on the engine speed and load, the Engine Control Module (ECM) adjusts the valve. To do this, it modulates a solenoid valve in the VVT which controls the engine oil pressure.
If the ECM detects an out-of-spec voltage in the VVT solenoid valve circuit, the DTC P0077 OBDII will be set.