VVT Actuator (Cam Phaser)

What it does

The VVT actuator, or cam phaser, is the part on the end of the camshaft that physically rotates to change valve timing when the solenoid sends it oil pressure. Inside is a locking pin and vanes. When they wear, you often hear a brief rattle on a cold start before oil pressure builds, and the computer may flag a timing-correlation code.