What it means
The ECU compares each cylinder's contribution to crankshaft speed (rough run analysis) and determined cylinder 1 contributes less or more than the average. This points to a mechanical or fuel delivery problem rather than a pure ignition fault.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The engine control module compares each cylinder's effect on crankshaft speed to assess how evenly the engine is running. P0263 indicates cylinder 1 contributes differently from the others, directing diagnosis toward its fuel delivery, compression, or local air leak rather than assuming an injector circuit fault.
Common causes
Most likely first.
- Injector clogged or worn
- Low compression on cylinder
- Localized intake leak
Symptoms
- Check-engine light on
- Rough idle or engine vibration
- Reduced engine power
- Poor acceleration
How to diagnose it
- Record freeze-frame data and review cylinder contribution or misfire data to confirm that cylinder 1 is the outlier.
- Inspect the intake area around cylinder 1 for a localized air leak and check for loose or damaged connections.
- Check cylinder 1's injector operation and compare its fuel delivery with the other cylinders using the manufacturer's procedure.
- Perform a compression test on cylinder 1 and compare the result with the manufacturer's specification and other cylinders.
- If needed, perform a leak-down or other mechanical test on cylinder 1 to identify an internal sealing problem.
Common fixes
- Repair a confirmed intake leak affecting cylinder 1.
- Clean or replace the cylinder 1 injector if its restricted or worn condition is confirmed.
- Repair cylinder 1 mechanical faults identified by compression or leak-down testing.
- Recheck cylinder contribution after the repair to verify it is balanced.
Can I keep driving?
Rough running and reduced power can worsen, and continued misfiring can damage the catalytic converter. Avoid heavy loads and stop driving if the engine shakes severely or the warning light flashes.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.