P234ACylinder 9 Pressure Sensor Circuit Low
- 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
- P234A means the signal of the cylinder 9 combustion pressure sensor stays below its permitted minimum. No published manufacturer document covers cylinder 9; the closest pattern is the GM-built 2.0 CDTI diesel of the Saab 9-5, whose cylinder 1–4 low codes (P0397 for cylinder 1) set after more than 2 s below threshold with the engine running, checked once per operating cycle, as Type B – the MIL comes on after the second failing trip. A scan tool then shows a peak pressure of 0 kPa. Electrically this points to a lost 5 V reference, a reference shorted to ground or a signal wire touching ground. Saab expects 3 to 12 Ohm between reference and ground at the plug. Combustion control for the cylinder is suspended, which usually goes unnoticed. The high counterpart is P234B.
- What you may notice
- Check engine light after two trips
- Peak pressure reads 0 kPa on the scan tool
- Driving behaviour mostly unchanged
- Likely causes
- Likely5 V reference interrupted or shorted to ground
- PossibleSignal wire shorted to ground
- PossibleSensor in the glow plug defective
- 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.