P234CCylinder 9 Pressure Sensor Circuit Intermittent/Erratic
- 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
- P234C covers a cylinder 9 combustion pressure signal that jumps or briefly drops out instead of staying permanently low or permanently high. As an analogue only the Saab 9-5 diesel (a GM 2.0 CDTI) is published: its erratic codes for cylinders 1–4 (P0399 for cylinder 1) react much faster than the low/high codes, already once the signal has left its window for longer than 0.2 s while the engine runs, and they are Type B. Before a new glow plug is fitted, the test plan there verifies a 5 V reference within 4.8 to 5.2 V and less than 5 Ohm on the ground. Loose contacts at the plug connector, a harness rubbing on the cylinder head or electronics that fail when hot are typical. The code tends to come and go; for cylinder 9 no manufacturer documents it.
- What you may notice
- Check engine light, often coming and going
- Fault stored but hard to reproduce in the workshop
- Likely causes
- LikelyIntermittent contact at the glow plug connector
- PossibleHarness rubbing on the cylinder head, breaking contact under vibration
- PossibleSensor electronics unstable at high temperature
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €50 – €450
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.