P0021 — A Camshaft Position - Timing Over-Advanced (Bank 2)
Moderate severityWhat it means
P0021 is stored when the engine control unit sees a fault involving the “A” (typically intake) camshaft timing/actuator on bank 2. Variable valve timing rotates the camshaft to optimise power and economy across the rev range; the control unit drives an oil-control valve and watches the resulting cam angle. “Timing over-advanced” means the variable valve-timing system has moved the camshaft further than commanded — or cannot hold the commanded angle — so valve timing is out.
Common symptoms
- A rattle on start-up or rough running
- Rough idle or a start-up rattle
- Loss of power or poor economy
- Hesitation at certain RPM
Likely causes
- A stuck camshaft phaser or oil-control valve
- Dirty oil or low oil pressure reaching the phaser
- A clogged oil-control valve or dirty/low oil
- A worn camshaft phaser or timing-chain stretch
What to check first
- Check oil level and condition first, then watch commanded vs actual cam angle in live data
- Check oil level and condition first
- Inspect the oil-control valve and its connector
Can you keep driving?
Often drivable, but timing faults hurt power and economy and can stress the chain — diagnose soon.
Frequently asked questions
What is the most common cause of P0021?
The most likely cause is: A stuck camshaft phaser or oil-control valve. Several other faults can set P0021 as well, so confirm the real cause with live data and the checks above before replacing any parts.
Can I just clear P0021 and keep driving?
Clearing P0021 with an OBD2 scanner turns the warning light off, but if the underlying fault has not been repaired the code will usually come back within a few drive cycles. Fix the cause first, then clear the code to confirm the repair worked.
How serious is P0021?
P0021 is a moderate-severity code. The car is often still drivable, but have it diagnosed soon — the underlying problem can get worse and it may fail an emissions test.
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