P03B5Cylinder 4 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 4. P03B5 means the sensor signal stays below its lower limit. GM's European 2.0 CDTI diesel (Saab 9-5, 2010) sets it when the signal is below 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 0 kPa instead of the normal 0–9,000 kPa. Saab names an open or grounded 5 V reference and a signal wire shorted to ground as causes; the glow plug should measure 3–12 Ω between reference and ground. 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
- 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.