P0266
PowertrainCylinder 2 Contribution/Balance Fault
This is usually a small-to-medium job, not an engine-out nightmare, so don't panic when you see it. The ECU monitors how much each cylinder contributes to keeping the engine turning smoothly, and it's flagged that cylinder 2 is pulling its weight less than the rest. Most of the time the culprit is a tired injector, a duff coil or a connector that's gone green at the pins, all of which are fixable without breaking the bank. The exception is if cylinder 2 has a compression problem, and that's the one that gets expensive.
ⓘ Information only. This page provides general educational information about fault code P0266. 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 P0266 mean?
P0266 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Cylinder 2 Contribution/Balance Fault.
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 flashing if there's a hard misfire alongside it
- • Lumpy idle when you're sat at the lights, often with a rhythmic shudder you can feel through the seat
- • Down on power, especially pulling away or going up a hill
- • Fuel economy slips, you'll notice the needle dropping faster than usual
- • Hesitation or a stumble at a steady cruise on the motorway
- • On worse cases the car drops into limp mode to protect itself
Possible causes
Causes commonly associated with P0266, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Sticking, clogged or worn injector on cylinder 2, the most common cause as injectors gum up over the years, particularly on direct-injection petrols and common-rail diesels
- 2. Failing or weak ignition coil on cylinder 2 on coil-on-plug petrols, the spark gets lazy under load and that cylinder stops contributing properly
- 3. Spark plug worn out or fouled on cylinder 2, cheap to check and quick to rule out
- 4. Corroded or loose injector connector, the pins go green or the locking tab cracks and the contact gets intermittent
- 5. Wiring damage in the injector circuit, chafing against the loom or rodent chewing being the usual suspects
- 6. Low compression on cylinder 2 from a burnt valve, worn rings or a head gasket starting to go, this is the costly one to find
- 7. PCM injector driver circuit fault, rare but it does happen and points the finger back at the ECU itself
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. Pull every stored and pending code first. A P0266 sitting next to a P0202 (injector circuit) or a P0302 (cylinder 2 misfire) tells you a lot about where to dig
- 2. Get a torch on the cylinder 2 injector connector and wiring. Look for green corrosion, a cracked locking clip, a pin pushed back, or loom that's rubbed through. This catches a fair share of them before you spend a penny
- 3. Watch live fuel trims with the engine running and warm. If short and long-term trims are swinging hard on bank 1, the ECU is fighting a fuelling problem on that cylinder
- 4. Run a cylinder contribution or balance test if your scan tool supports it, then compare cylinder 2's output directly against the others to confirm it really is the weak one
- 5. Measure the injector resistance, you're looking for something in the region of 12 to 16 ohms on a typical petrol or 20-odd on others, and compare it to a healthy cylinder on the same engine
- 6. If fuelling and ignition all check out, do a compression or leak-down test on cylinder 2. A low reading there means the problem is mechanical and the bills go up from here
Common questions about P0266
How long can I keep driving like this before something gives? +
You can usually limp it to a garage, but don't make a habit of it. A cylinder that isn't burning its fuel properly dumps raw fuel into the exhaust, and over weeks that can cook the catalytic converter, which turns a £200 injector job into a job with a four-figure cat on top. If it's running really rough or it's dropped into limp mode, get it looked at this week rather than this month.
Is it the injector itself or just a dodgy wire or plug? +
Both are common, which is why you check the cheap stuff first. A connector full of corrosion or a chafed wire will throw this code while the injector is perfectly healthy, so a five-minute inspection of the plug and loom can save you buying a part you don't need. If the wiring is clean and the resistance reads right, then suspicion shifts to the injector or the coil. Test the wiring before you reach for your wallet.
How long does the repair actually take? +
A coil or spark plug swap on most engines is half an hour. A single injector on an accessible petrol is usually one to two hours of labour, more on a diesel where the rail and pipes are buried or where the injector is seized into the head. If it turns into a compression job needing the head off, you're looking at a full day or more in the garage, so confirm the cause before agreeing to that work.
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 →