A P0021 DTC trouble code may be caused by one or more of the following:
Incorrect camshaft timing
Wiring problems (harness/wiring) in intake timing control valve control solenoid system
Continuous oil flow to VCT piston chamber
Failed timing valve control solenoid (stuck open)
A code P0021 refers to the VVT (variable valve timing) or VCT (variable camshaft timing) components and the car's PCM (powertrain control module, also called an ECM). That consists of a few different components but the P0021 DTC specifically refers to the camshaft (cam) timing. In this case, if the cam timing is above a set limit (over-advanced), the engine light will be illluminated and the code will be set. The "A" camshaft is either the intake, left, or front camshaft. A P0021 engine code is basically the same as a P0011 code, except this is for Bank 2, not Bank 1.
The first thing I'd do is check oil level- low oil will also cause this. Also if you put too heavy weight oil could be restricting oil pressure.
Hope this helps.