P03C9Cylinder 6 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
- 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 6. P03C9 means the sensor signal stays below its lower limit – typically an open or grounded 5 V reference or a signal wire shorted to ground. The only manufacturer we found using this code family, GM's European 2.0 CDTI four-cylinder diesel (Saab 9-5, 2010), uses it for cylinders 1 to 4: signal below the threshold for more than 2 s with the engine running, check engine light after two trips, displayed pressure 0 kPa. For cylinder 6, which only engines with at least 6 cylinders have, no manufacturer document available to us uses the code; the description follows that logic and CARB. Without the signal, combustion control for this cylinder is switched off.
- 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
- Likely5 V reference wire open or shorted to ground
- PossibleSignal wire shorted to ground
- PossibleSensor electronics of the glow plug faulty
- RareEngine module supplies no reference
- 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.