P2351: Cylinder 9 Combustion Performance
What to do
One cylinder measurably underperforming is usually one injector's story on a diesel — and the per-cylinder data that stored this code is exactly what a workshop should show you when explaining the diagnosis.
What this code means
Cylinder 9's combustion, watched directly through its pressure trace, is underperforming — the family's summary verdict, stored when the burn is consistently weak, late or incomplete without a more specific code claiming why.
Read it as a measured version of what a misfire code infers: the module is not guessing from crankshaft ripple, it has watched this cylinder burn badly. The suspect list is the per-cylinder classics in diesel order — injector delivery, compression, glow plug on cold-start complaints — with the sensor itself last, checked against its siblings by the overrun comparison at P2349.
Likely causes
Start here
- Failed fuel injector · moderate
Less common
- Low engine compression · specialist
- Failed glow plug · easy
- Faulty cylinder pressure sensor · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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