P2348: Cylinder 9 Pressure Sensor Circuit
What to do
The engine runs on its fallback estimates for that cylinder — usually imperceptible. Wiring and connector first, as ever; if the sensor itself is condemned, know that on most diesels it is integrated into the glow plug, and price accordingly rather than accepting a mystery line item.
What this code means
The pressure sensor inside cylinder 9 has failed its circuit checks — and the existence of such a sensor is the page's real subject, because most engines have nothing like it.
Everything else the module knows about combustion is inference. Misfire detection reads crankshaft speed ripples; knock sensors listen through the block; oxygen sensors examine the aftermath in the exhaust. An in-cylinder pressure sensor is the module watching combustion directly — the full pressure trace of every firing stroke, per cylinder, per cycle — which turns fuelling and timing into closed-loop control at the level everything else only estimates. On diesels, where these sensors mostly live, the sensor is typically built into the glow plug (a pressure-sensing glow plug), which is worth knowing before anyone quotes: replacing the sensor is a glow plug job, and the part costs several times a plain plug.
Cylinder 9 places the engine. These codes exist for cylinders nine through twelve, so they only ever appear on V10 and V12 engines — large diesels and flagship petrols. A circuit fault here is the block's standard electrical story: the module falls back to running that cylinder on inference like an ordinary engine, so the felt symptom is often nothing at all, with slightly coarser running the honest maximum.
Likely causes
Start here
- Open circuit in sensor wiring · moderate
- Corroded or loose connector · easy
Less common
- 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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