P0263 to P0266: cylinder contribution and balance faults

A misfire code says a cylinder failed to fire. A contribution or balance code says something more subtle: the cylinder fired, but it produced measurably less torque than its neighbours.

That is a lower threshold, and it is why these codes often appear before any misfire does.

Cylinder	Circuit: low / high	Contribution and balance
1	P0261 / P0262	P0263
2	P0264 / P0265	P0266
3	P0267 / P0268	P0269
4	P0270 / P0271	P0272

The codes run in threes per cylinder, and the balance code is every third one. The pattern continues the same way: P0275 for cylinder 5, P0278 for cylinder 6.

Some manufacturers number cylinders differently from the physical layout, so check the description your tool gives rather than assuming from the number.

Related: P0301 to P0304 cylinder misfire diagnostics.

How the ECU measures contribution

Not by looking at combustion directly — it cannot. It watches crankshaft acceleration.

Each firing event gives the crankshaft a push, and the crank position sensor resolves that push as a tiny speed change. A cylinder contributing less produces a smaller push, and the ECU sees it in the crankshaft signal.

The same technique underlies misfire detection: how the misfire monitor works.

What causes one cylinder to under-perform

On a diesel: the injector, usually

An injector delivering slightly less than commanded, or with degraded spray pattern, contributes less torque. This is the most common cause by a wide margin.

Where the system exposes them, injector correction values name the cylinder directly — the ECU has already been compensating and will tell you by how much: injector correction values on EDC17.

A correction value drifting steadily on one cylinder over months is an injector approaching the end of its life, visible long before any symptom.

Compression

A cylinder with lower compression makes less torque, full stop. Causes: worn rings, a burnt valve, a valve out of adjustment, or a head gasket beginning to fail.

A contribution code that does not respond to injector work needs a compression test. This is where the diagnosis leaves the scan tool.

Fuelling supply to that cylinder

A restricted injector feed pipe, or on a petrol engine a clogged injector, produces the same result.

Wiring

An injector circuit with added resistance opens slightly late or closes slightly early. Check the connector before condemning the injector: P0201 to P0206 injector circuit diagnostics.

Reading the pattern across cylinders

The distribution is the diagnosis.

Pattern	Points at
One cylinder only	Injector, compression or wiring on that cylinder
Adjacent pair	Head gasket between them, or a shared feed
All cylinders on one bank	Bank-specific supply or sensor
All cylinders	Not a balance fault — check fuel supply overall

Adjacent cylinders is the one worth knowing. A head gasket failing between two cylinders lets compression leak from one to the other, and both read low.

Symptoms

Often mild, which is the point:

• A slight vibration at idle that is easy to attribute to age.
• Marginally worse fuel consumption.
• A faint hesitation under light load.
• Sometimes nothing perceptible at all.

That subtlety is what makes these codes valuable. They catch a developing fault while it is still a single injector rather than a misfire, a damaged catalyst and a tow home.

Engine misfire troubleshooting covers what happens when it progresses.

The diagnostic sequence

1. Note which cylinder the code names, and read the description rather than guessing from the number.
2. Read injector correction values if the vehicle exposes them.
3. Check misfire counters per cylinder — is the same one accumulating?
4. Swap components between cylinders where practical on a petrol engine: move a coil or an injector to a different cylinder and see whether the code follows.
5. Compression test if injector work does not resolve it.

Step four is the classic and still the best. If the fault moves with the part, you have identified it without buying anything.

Do not clear and hope

Contribution codes describe a measured shortfall. Clearing them removes the record without changing the measurement, and the code returns as soon as the monitor runs again.

Worse, clearing wipes the freeze frame and the injector correction history that would have told you how long this has been developing.

Clearing codes: when and why.

Try it on the free tier of the app — pair an ELM327 adapter and check misfire counters by cylinder alongside any balance code. Two data sets naming the same cylinder is a diagnosis, not a coincidence.