WHAT ARE CAM PHASERS?
Cam phasers are components in the VCT system that adjust camshaft timing. By advancing or retarding the camshaft position, they help improve fuel efficiency, power, and emissions. When working correctly, they dynamically change the timing depending on engine speed and load.
What Causes the Rattle?
The rattle you hear—especially on cold starts—is caused by a
faulty cam phaser lock pin. At idle, the system is designed to lock the phasers in a fixed position. But when the lock pin fails:
- The phaser doesn’t stay in position after shutdown
- Oil drains from the phaser chambers
- On startup, until oil pressure builds up, the loose phaser rattles
This condition can also lead to poor cam timing, triggering the
check engine light, rough idling, and in severe cases,
engine damage.
