P0398Cylinder 1 Pressure Sensor Circuit High
- 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
- Some diesels have a combustion pressure sensor in the glow plug; the engine module uses it to control injection for each cylinder. This code concerns cylinder 1. P0398 means the sensor signal stays above its upper limit. GM's European 2.0 CDTI diesel (Saab 9-5, 2010) sets it when the signal is above the threshold for more than 2 s with the engine running, checked once per drive cycle, with the check engine light after two trips; the displayed maximum combustion pressure then reads 10,000 kPa instead of the normal 0–9,000 kPa. Saab names a 5 V reference shorted to positive, an open signal wire or one shorted to positive, and an open ground wire as causes – an unplugged connector is the most common. Without the signal, combustion control for this cylinder is switched off, which is usually barely noticeable.
- What you may notice
- Check engine light on (often after two trips)
- Usually barely noticeable – combustion control for the cylinder is switched off
- Possibly rougher running, more noise or slightly higher consumption
- Likely causes
- LikelyConnector off or loose, signal wire open
- PossibleSensor ground wire open
- PossibleSensor in the glow plug faulty
- RareSignal or reference wire shorted to positive
- 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 – €400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.