Faulty or partially blocked cylinder 1 fuel injector (electrical or mechanical fault); Damaged wiring or poor connector contact on the cylinder 1 injector circuit; Low compression in cylinder 1 (worn rings, burnt valve, head gasket leak); Worn or faulty spark plug or ignition coil on cylinder 1 (petrol engines); Air or vacuum leak, or carbon build-up at cylinder 1 intake port; Fuel supply fault such as low rail pressure affecting the injector; Fault in the engine control unit injector driver.

P0263

Cylinder 1 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)
63: FaultThe specific fault in that area

What it means

P0263 means the engine control unit has found that cylinder 1 is not contributing as much as the other cylinders during the power balance (contribution) test. It sets when the engine speed change or fuel correction for that cylinder differs from the rest by more than the allowed limit. The fault points to the cylinder 1 injector circuit or injector, but the exact test and cause depend on the engine and fuel type.

Symptoms

Rough idle or uneven running, often with a misfire feel
Engine management light on
Loss of power or poor acceleration
Increased fuel consumption
Hard starting or extra vibration at idle
Black or blue smoke from the exhaust on some engines

Possible causes

Faulty or partially blocked cylinder 1 fuel injector (electrical or mechanical fault)likely
Damaged wiring or poor connector contact on the cylinder 1 injector circuitlikely
Low compression in cylinder 1 (worn rings, burnt valve, head gasket leak)possible
Worn or faulty spark plug or ignition coil on cylinder 1 (petrol engines)possible
Air or vacuum leak, or carbon build-up at cylinder 1 intake portpossible
Fuel supply fault such as low rail pressure affecting the injectorrare
Fault in the engine control unit injector driverrare

How to diagnose

Read all stored and pending codes and freeze frame data, noting engine load, speed and temperature when the fault set
Check for other misfire, injector or fuel trim codes that point to a wider problem
Inspect the cylinder 1 injector wiring and connector for damage, corrosion, chafing or loose pins
On petrol engines, inspect the cylinder 1 spark plug and coil, and swap the coil with another cylinder to see if the fault follows
Check live data for cylinder balance or misfire counts per cylinder and compare with the other cylinders
Test injector electrical resistance and driver signal against the manufacturer's specification for that engine
Carry out a compression or leak-down test on cylinder 1
Check fuel pressure and look for intake leaks, following the procedure for that model

How to fix

Repair or replace damaged wiring or connectors on the cylinder 1 injector circuit
Replace or have the cylinder 1 injector cleaned or recalibrated as the manufacturer specifies
Replace the worn spark plug or faulty ignition coil on cylinder 1
Repair the mechanical fault causing low compression, such as valves, rings or head gasket
Fix any intake or vacuum leaks and clean carbon deposits as the engine design requires
Rectify fuel supply faults found during pressure testing

Can I keep driving?

Medium severity

The car can usually be driven gently for a short time, but get it checked soon. Continued misfiring or poor combustion can damage the catalytic converter and engine, so avoid heavy loads, and stop if the warning light flashes or the engine runs very roughly.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.