P0021
Powertrain"A" Camshaft Position - Timing Over-Advanced or System Performance (Bank 2)
The ECU watches where the bank 2 intake camshaft actually sits compared to where it told the cam phaser to put it. When the cam stays advanced beyond what was commanded, it logs P0021. For you, that means the variable valve timing on one bank is stuck or being pushed too far forward, and the engine can't time itself properly. Bank 2 is the side of the engine that doesn't have cylinder number one, which matters on V6 and V8 layouts where the two banks each have their own phaser and solenoid.
ⓘ Information only. This page provides general educational information about fault code P0021. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0021 mean?
P0021 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: "A" Camshaft Position - Timing Over-Advanced or System Performance (Bank 2).
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light on, sometimes with a rough idle alongside it
- • Lumpy or hunting idle that won't settle, worse from cold
- • Hesitation or a flat spot when you put your foot down
- • Hard starting, particularly first thing on a cold morning
- • Down on power on hills or when the engine is working hard
- • Fuel economy creeping worse over a tank or two
- • Occasional stall at junctions or when coming to a stop
Possible causes
Causes commonly associated with P0021, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. VVT solenoid (oil control valve) on bank 2 stuck open or sticking. This is the usual offender, and it's often gummed up rather than electrically dead
- 2. Dirty, low, or wrong-grade oil starving the cam phaser of clean pressure. VVT systems are fussy about oil. A car that's missed services is prime for this
- 3. Cam phaser itself worn or seized in the advanced position, common on higher-mileage engines where the locking pin and vanes are worn
- 4. Oil galleries and the OCV screen clogged with sludge, choking the oil feed to the phaser
- 5. Camshaft position sensor on bank 2 reading inaccurately, so the ECU thinks the cam is over-advanced when it isn't
- 6. Damaged or corroded wiring or connector at the solenoid, throwing intermittent readings
- 7. Timing chain stretched or jumped a tooth on bank 2, which is the expensive end of the list
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Check the oil first, level and condition. Pull the dipstick and look for black, thin, or low oil. A surprising number of P0021s clear up after a proper oil and filter change with the correct grade
- 2. Read the codes and look at freeze frame data to see what the engine was doing when it logged. Cold start, hot idle, and under load all point in different directions
- 3. Scope the commanded versus actual cam angle on bank 2 with a live-data scan tool. If the actual angle stays advanced when commanded back, the phaser or solenoid is the problem
- 4. Inspect the bank 2 solenoid connector and wiring for corrosion, oil contamination, or a loose pin before condemning the part
- 5. Command the VVT solenoid on and off with a bi-directional tool, or pull it and bench-test it. A solenoid that doesn't click cleanly or has the wrong resistance gets binned
- 6. If the solenoid, sensor, and wiring all check out, you're looking at the phaser or the timing chain, and that's a strip-down job
Common questions about P0021
Can I keep driving it for now? +
For a short stint, yes, if it's running but a bit rough. The risk is that a phaser stuck advanced can put the engine in limp mode and, on the worst cases, lead to timing components wearing faster. If the idle is bad or you're losing power, get it looked at within days rather than weeks. Don't ignore it for months on the assumption it's just a light.
Is this going to fail my MOT? +
P0021 on its own isn't an MOT line. What fails you is the engine warning light being on when the tester looks at the dash, since an illuminated MIL is a fail on its own now. If you've sorted the cause, drive a few cycles so the light goes out before you take it in. A rough-running engine could also tip the emissions check over the limit.
What's it likely to cost to sort? +
If it's just oil, you're into the cost of an oil and filter change, call it £60 to £120 at an independent. A VVT solenoid is a cheap part, often £30 to £90, with maybe an hour's labour, so figure £100 to £250 fitted at an independent and more at a main dealer. A cam sensor is similar money. If it turns out to be the phaser or the timing chain, you're into the high hundreds and easily over a grand on a V6 where they have to come deep into the front of the engine.
How do I tell which of these it actually is on my car? +
Start with the cheapest and most common. Check the oil. If it's filthy or low, change it and clear the code, because a clogged solenoid often frees up once it sees clean oil. If the fault comes straight back, scope the commanded versus actual cam angle: a solenoid or phaser issue shows the actual angle ignoring the command, while a duff sensor tends to give erratic or impossible readings. Wiggle-test the connector to rule out wiring. If the live data is clean but the angle is still wrong, suspect the phaser, and a jumped timing chain usually brings a P0016 or P0017 along with it.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →