P0266 Cylinder 2 Contribution/Balance — Causes & Fix
Updated for 2026 diagnostics & repair guidance
P0266 at a Glance
What it means
The ECU has detected that cylinder 2 is contributing less power than the other cylinders.
Most common cause
Worn or failing cylinder 2 injector, causing uneven fuel delivery.
Severity
Moderate — driveable but causes rough running and increased emissions.
Can you drive?
Yes, but performance is reduced. Address within 1–2 weeks.
Typical repair cost
£100–£350 for injector replacement.
What Does P0266 Mean?
P0266 indicates the Engine Control Unit (ECU) has detected a power imbalance in cylinder 2. The ECU continuously monitors crankshaft acceleration after each cylinder fires — when cylinder 2 contributes noticeably less torque than the others, P0266 is set. This is almost always caused by a degraded injector that is delivering too little or too much fuel.
Common Causes
Injector-Related Causes
Worn cylinder 2 injector nozzle
Over time the injector nozzle wears, altering the spray pattern and reducing combustion efficiency in cylinder 2.
Injector drift (calibration loss)
The cylinder 2 injector's delivery quantity has drifted outside the ECU's compensation range, causing a measurable balance fault.
Carbon build-up on injector tip
Carbon deposits on the injector nozzle restrict fuel flow and distort the spray pattern, reducing cylinder 2 output.
Other Possible Causes
Low compression in cylinder 2
Worn piston rings or valves in cylinder 2 reduce compression, preventing proper combustion regardless of injector quality.
Glow plug failure (cylinder 2)
A failed glow plug in cylinder 2 can cause cold-start misfires that set a contribution fault code.
Symptoms Drivers Notice
- Rough idle with a rhythmic miss
- Slight vibration through steering wheel at idle
- Reduced power under acceleration
- Marginally higher fuel consumption
- Engine management light illuminated
- Occasional puff of black or white smoke
Vehicles Commonly Affected
Can You Still Drive with P0266?
Yes — P0266 is driveable. You'll notice rough idle and slightly reduced power but no immediate safety risk. Address within 1–2 weeks to prevent DPF problems from incomplete combustion. If idle becomes very rough or you notice heavy smoke, have it inspected sooner.
How Mechanics Diagnose P0266
- 1
Read cylinder contribution values
Use a diagnostic tool to read live cylinder balance data. Cylinder 2 will show a negative deviation (e.g., -15% or worse).
- 2
Perform injector leak-off test
Measure fuel return from the cylinder 2 injector. Elevated return (>15ml/min) confirms injector wear.
- 3
Swap injectors between cylinders
Swap cylinder 2 injector with a known-good cylinder. If the fault follows the injector, it's confirmed as the cause.
- 4
Check injector coding
Verify the injector IMA/QR code for cylinder 2 is correctly programmed in the ECU. Incorrect coding causes balance faults.
- 5
Compression test cylinder 2
If the injector checks out, perform a compression test to rule out mechanical wear in cylinder 2.
Repair Solutions & Costs
Replace cylinder 2 injector
The most common fix. A remanufactured injector restores correct fuel delivery and cylinder balance.
Injector cleaning (ultrasonic)
If carbon build-up is the cause and the nozzle isn't worn, professional cleaning can restore performance.
Re-code injector to ECU
If the injector is physically fine but incorrectly coded, reprogramming the IMA code resolves the balance fault.
Replace glow plug (cylinder 2)
If the glow plug has failed, replacement resolves cold-start misfires that set the contribution code.
When Injector Replacement Is Required
Replacement is required when the leak-off test shows elevated return flow, the cylinder contribution is more than 15% below average, or the injector has more than 100,000 miles of use.
Compatible Injector Part Numbers
5 injectors compatible with engines affected by P0266.
Cross Reference Numbers
OEM and alternative part numbers for injectors affected by P0266.
Affected Vehicle & Engine Combinations
Need a Replacement Injector?
UK-tested remanufactured injectors with 12-month warranty. Search by engine code or vehicle registration.
Need it fast? Same-day dispatch on in-stock injectors.
Order before 2pm for next working day delivery (UK mainland). Call us on 020 3355 6581.
Engine-Specific Guides
Frequently Asked Questions
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