P2351Cylinder 9 Combustion Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- P2351 does not concern the sensor but the quality of combustion in cylinder 9, as judged from the pressure trace: the energy released per cycle, or its balance against the other cylinders, falls outside the permitted window. No manufacturer documents the code publicly, nor its cylinder-1 analogue P039E. CARB explains why such a check exists: engines fitted with combustion or combustion-quality sensors, such as homogeneous-charge compression-ignition designs, must catch misfire far more sensitively than others. Typical root causes are a coked or leaking injector, partial loss of compression, an air leak upstream or poor fuel. The engine runs unevenly, smoke rises, and the problem frequently shows up alongside a pressure too low/high code or a cylinder 9 misfire code.
- What you may notice
- Check engine light on
- Uneven running and vibration
- Increased smoke and fuel consumption
- Likely causes
- LikelyInjector of cylinder 9 coked, leaking or sticking
- PossiblePartial compression loss in cylinder 9
- RarePoor fuel quality or water in the fuel
- RarePressure sensor distorting the evaluation
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €150 – €2,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.