The underlying cause is most likely among these possibilities: 1) blocked oil passages due to sludge; 2) faulty wiring to the camshaft oil control valve; 3) a faulty camshaft oil control valve; or 4) faulty timing chain and / or camshaft phasers... (yourmechanic.com)
You might also replace your cylinder deactivation solenoid # 7 or clear your cylinder deactivation solenoid oil passages of dirt and debris. (yourmechanic.com)