M274 timing chain rattle on cold start: how much is normal, and when the camshaft adjusters have to come out

A two-second rattle on a cold M274 is the camshaft adjusters bleeding down, and Mercedes revised them. A rattle that lasts longer, or a correlation code, is the chain.

Mercedes' M274 uses hydraulic camshaft adjusters that hold oil pressure to keep the phaser locked at rest. Early units bled down overnight, so on the first start the phaser flaps until pressure builds. Mercedes released revised adjusters with a better locking pin.