- Dirty Oil
- Variable Valve Timing (VVT) circuit is open or shorted
- Oil Control Valve (OCV) circuit is open or shorted
- Faulty variable valve timing (VVT)
- Faulty oil control valve (OCV)
- Damaged ECM

There is a factory service bulletin for following Scion models.


2005-2006 Scion xA
2006-2006 Scion xB


Scion Service Bulletin OBDII Code P0012

After the ECM sends the target dutyandcycle signal to the OCV, the ECM monitors the OCV current to establish an actual duty cycle. The ECM determines the existence of a malfunction and sets the DTC when the actual dutyandcycle ratio varies from the target dutyandcycle ratio.

- Engine Light ON (or Service Engine Soon Warning Light)
- Lack/Loss of power
- Engine rough idle

The Engine Control Module (ECM) controls the Oil Control Valve (OCV) to regulate the intake camshaft angle. As a result of the angle change, the engine timing is advance or retard. Optimizing engine timing will help the engine improve torque and fuel economy, and the exhaust emissions decrease under overall driving conditions. The Variable Valve Timing (VVT) system includes the Oil Control Valve (OCV) and VVT controller. The ECM detects the actual intake valve timing using signals from the camshaft and crankshaft position sensors, and performs feedback control.