Camshaft tone ring slips
M274Check engine light and a timing-implausible code, often with no noise and no obvious running fault.
The tone ring can turn independently of the camshaft it is mounted on, so the sensor reports a timing position the engine is not actually in. The chain and the adjuster can both be perfectly good — which is why this one gets misdiagnosed as a chain job and paid for twice.
Codes a scan would show: P001685, P0015
Checked against forums.mbclub.co.uk

