OBD-II trouble code
P0266: Cylinder 2 Contribution/Balance Fault
Cylinder 2 is producing less power than the rest, measured by watching crankshaft speed after each power stroke. Fuel, spark, or compression can all cause it — test before replacing parts.
Quick facts
- System
- Powertrain
- Category
- Fuel Injectors
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $100 – $3,000
- DIY difficulty
- Intermediate DIY
What does P0266 mean?
P0266 belongs to the contribution/balance family — the codes in the P02xx injector block that measure results rather than wiring. The engine control module (ECM) watches crankshaft rotational speed through the crankshaft position sensor. Every combustion event gives the crankshaft a brief acceleration, and the size of that acceleration is a direct measure of how much work the cylinder did. The ECM compares all cylinders against each other, and when cylinder 2's share falls outside the allowed spread, P0266 sets.
The critical thing to understand is that the ECM is not measuring the injector. It is measuring the outcome. Anything that weakens cylinder 2 will produce this code with identical fingerprints: a restricted or slow injector, a worn plug or dying coil on a gasoline engine, or a mechanical loss of compression from worn rings, a leaking valve, or a head gasket.
There is one detail that trips people up more on cylinder 2 than on cylinder 1: cylinder numbering. The ECM's 'cylinder 2' is the manufacturer's cylinder 2 in the engine's own numbering scheme, not the second injector from the front of the engine bay and not the second position in the firing order. On V6 and V8 engines the two banks are numbered differently between manufacturers — and getting it wrong means testing a perfectly healthy cylinder. Confirm the layout in the service information before pulling anything.
One more practical point: if the same weak cylinder also throws a misfire code (P0302), you have two views of the same failure and can be confident the problem is real. A balance fault with no misfire code often means a milder problem — an injector that is dirty rather than dead, or a cylinder starting to lose compression — which is a good stage to catch it at.
Common causes
- Clogged or restricted cylinder 2 fuel injector from carbon or fuel contamination
- Slow or internally worn injector that opens late and delivers less fuel per pulse
- Worn spark plug or failing ignition coil on cylinder 2 (gasoline engines)
- Low compression on cylinder 2 from worn rings, a burnt valve, or a valvetrain problem
- Head gasket leaking between cylinder 2 and a neighboring cylinder
- Vacuum or intake gasket leak affecting only the cylinder 2 runner
- Low fuel pressure or a plugged fuel filter that shows up first on one cylinder
- Corroded connector or damaged wiring at the cylinder 2 injector
Symptoms
- Check engine light on
- Rough idle with a distinct shake
- Reduced power and sluggish acceleration
- Companion misfire codes such as P0302 or P0300
- Poor fuel economy
- Extended cranking or hard starts, particularly on diesel engines
- Exhaust smell of unburned fuel
Diagnostic steps
- 1.Read every stored code. P0264, P0265, or P0202 present with P0266 means an electrical fault on the cylinder 2 injector circuit — fix that first, because the balance fault follows from it.
- 2.Confirm which physical cylinder your manufacturer calls number 2. This is the single most common wasted step on this code, especially on V6 and V8 engines.
- 3.Run a cylinder balance or injector contribution test on a capable scan tool and record how far cylinder 2 sits from the rest.
- 4.On a gasoline engine, inspect the cylinder 2 spark plug against the others. Fouling, heavy wear, or oil on the electrode explains the weak contribution immediately.
- 5.Swap the cylinder 2 ignition coil with an adjacent cylinder, clear codes, and drive. If the fault follows the coil, you are done.
- 6.Compression- and leak-down-test cylinder 2 before buying an injector. This is the step that separates a fuel problem from a worn engine, and skipping it is how people end up with a new injector and the same code.
- 7.Check fuel rail pressure under load and inspect the fuel filter for restriction.
- 8.Use a stethoscope or an injector buzz test to verify the cylinder 2 injector is clicking and responding to the ECM's pulse.
- 9.As a final confirmation, swap the cylinder 2 injector with one from a healthy cylinder. If the balance fault moves with the injector, replace it.
Repair cost
$100 – $3,000
A spark plug or coil on the affected cylinder typically runs $100-$350 installed. Fuel injectors are $60-$400 in parts plus 0.5-3 hours of labor on a gasoline engine; diesel injectors commonly reach $400-$900 each installed. Fuel supply repairs generally land between $150 and $800. Mechanical causes — rings, a valve, or a head gasket — start near $1,200 and can exceed $3,000. Expect $100-$200 for diagnosis, since this code demands testing rather than a single reading.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with fuel injector replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.