I have a 2006 2.4l or 130000 miles on it. And have code p0315. I understand I have to go to dealer to get the system relearn.. my question is what are the causes for the code p0315/ variable valve timing to forget what was learned??
Update

got back from the dealer no problems with timing chain or components. They did the relearn and everything seems to be operating at 100%.. thank you everyone for the help

 

The most common cause is worn timing chain and guides, have you changed any of that?
It would be a safe bet that if not you should pop off the valve cover and the front engine cover to verify any damage to the guides and slack in the chain.
I strongly suggest do not run the engine and do not try and turn the crankshaft counter clockwise.


https://www.obd-codes.com/p0315

 

And. It doesn't have to go to a dealer for the relearn procedure if needed. Any competent shop with the correct equipment can do the work.

 

The usual reason is that the sensor was changed or the crankshaft was turned with no timing chain or the ECM was changed.

It means there is no data about the variation stored in the computer, not necessarily a fault.