P0266
Cylinder 2 Contribution/Balance.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 2
- AreaFuel and air metering (injector circuit)
- 66
- FaultThe specific fault in that area
What it means
P0266 means the engine control unit has found that cylinder 2 is contributing less than the other cylinders during the cylinder balance (contribution) test. The ECU monitors crankshaft speed changes and fuelling corrections, and it saw cylinder 2 delivering too little power. The code is generic, so the exact cause and the test method vary by engine and model, and it is most often seen on diesel engines.
Symptoms
- Rough idle or uneven running
- Engine misfire or hesitation under load
- Loss of power
- Engine management light on, possibly flashing
- Increased smoke, fuel smell or poor fuel economy
- Hard starting or knocking noise from one cylinder
Possible causes
- Faulty or worn fuel injector on cylinder 2 (blocked, leaking, sticking or electrically failed)likely
- Wiring or connector fault in the cylinder 2 injector circuit (chafing, corrosion, poor pin tension)possible
- Worn or faulty spark plug or ignition coil on cylinder 2 on petrol engines, or a failed glow plug on diesels where relevantlikely
- Low compression on cylinder 2 (worn rings, burnt valve, head gasket leak)possible
- Intake air leak or restricted airflow affecting cylinder 2, such as a leaking inlet manifold gasket or carbon build-uppossible
- Low fuel pressure or poor fuel quality causing uneven deliveryrare
- Fault in the engine control unit injector driverrare
How to diagnose
- Read all stored and pending codes and the freeze frame data, noting engine speed, load and temperature when the fault set. Check for related misfire or injector codes.
- Check for any technical service bulletins or known issues for the specific engine.
- Visually inspect the cylinder 2 injector, coil and plug wiring and connectors for damage, corrosion, oil or coolant contamination.
- On petrol engines, inspect the spark plug and swap the coil with another cylinder to see if the fault follows it.
- Use live data to view cylinder balance or injector correction values and compare cylinder 2 with the others.
- Check for air leaks around the inlet manifold and look for vacuum or boost leaks.
- Test the injector circuit and injector resistance or operation as per the manufacturer's procedure for that engine.
- Carry out a compression or leak-down test on cylinder 2 if the fuel and ignition checks are all fine.
How to fix
- Repair or replace the faulty cylinder 2 injector, following any coding or adaptation steps the manufacturer specifies.
- Repair damaged wiring or connectors in the injector or ignition circuit.
- Replace the worn spark plugs and the faulty ignition coil, or the faulty glow plug where applicable.
- Repair the mechanical fault found by compression or leak-down testing, such as valve, ring or head gasket repairs.
- Fix any intake leaks by replacing gaskets or seals, and clean carbon deposits as the manufacturer recommends.
- Correct fuel supply problems such as low pressure or contaminated fuel, then clear the code and confirm with a road test.
Can I keep driving?
The car can be driven for a short time if it runs reasonably smoothly, but get it checked soon, as continued misfiring or a poorly running cylinder can cause further engine damage. If the warning light is flashing or the engine runs very roughly, stop driving and get it looked at.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.