Camshaft Phaser (VVT Actuator)

Most are oil-pressure operated vane units; some are electric. A solenoid valve controls oil flow to the phaser. It is a key part of variable valve timing. Some engines lock the phaser with a pin at start-up; a worn lock pin causes the typical brief rattle. Timing chain stretch can produce similar correlation codes.

Oil pressure moves vanes inside the phaser, advancing or retarding the cam.

Worn phasers can rattle briefly at start-up and set timing codes. Clean oil of the correct grade is essential.