Bank 2 cam timing over-advanced / VarioCam performance fault. On Porsche flat-sixes a persistent P0021 can indicate a mechanical cam-timing problem, not merely a sensor.
SYMPTOMS
- Check-engine light
- Rough running
- Power loss
- Possible limp mode
LIKELY CAUSES
- Failed adjuster or oil control valve
- Low oil pressure
- Clogged oil galleries
- Severe: spun cam bearing/gear
DIAGNOSIS STEPS
- Check oil level and pressure
- Replace oil control valve and cam sensor first
- If it persists, inspect cam timing mechanically with specialist tooling
RELATED PARTS
- VarioCam adjuster
- Oil control valve
- Camshaft position sensor