P2351 code meaning
Cylinder 9 Combustion Performance
Powertrain system Generic code P23xx codes Check engine light
What P2351 means
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.
P2351 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyHard
- Typical labor1 to 8 hours
- Clears after repairAfter a drive cycle
Symptoms of P2351
- Check engine light on
- Uneven running and vibration
- Increased smoke and fuel consumption
Common causes of P2351
- Most likelyInjector of cylinder 9 coked, leaking or sticking
- PossiblePartial compression loss in cylinder 9
- Less likelyPoor fuel quality or water in the fuel
- Less likelyPressure sensor distorting the evaluation
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Cylinder pressure sensor glow plugSensor wiringEngine control moduleFuel injector
What each part of P2351 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 3 | Area: ignition system or misfire. |
| 51 | The exact fault in that area. |
What to do next
- Note P2351 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P2351
What does P2351 mean?
P2351 means "Cylinder 9 Combustion Performance". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P2351?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P2351 fail an emissions test?
Yes, it can. P2351 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P2351 to fix?
Difficulty: hard. A typical repair takes 1 to 8 hours of work. This is a job for a workshop.
Will P2351 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.