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 3. P03AB 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.
Medium severity. Can I keep driving?If the car is running normally, drive in moderation to a repair shop. If it loses power or another warning appears, do not continue.
Cylinder 3 is numbered according to the manufacturer: check your engine's manual before working on it.
Symptoms
- 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
Most likely causes
- 5 V reference wire open or shorted to ground
- Signal wire shorted to ground
- Sensor electronics of the glow plug faulty
- Engine module supplies no reference
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It affects emissions.
What each character of P03AB means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- 3: Ignition and misfires
- AB: Specific fault in that system
Frequently asked questions
Can I keep driving with code P03AB?
If the car is running normally, drive in moderation to a repair shop. If it loses power or another warning appears, do not continue.
What causes code P03AB?
The most common causes are: 5 V reference wire open or shorted to ground; signal wire shorted to ground; sensor electronics of the glow plug faulty.
Related codes
- P03A9Cylinder 3 Pressure Sensor Circuit
- P03AACylinder 3 Pressure Sensor Circuit Range/Performance
- P03ACCylinder 3 Pressure Sensor Circuit High
- P03ADCylinder 3 Pressure Sensor Circuit Intermittent/Erratic
- P0397Cylinder 1 Pressure Sensor Circuit Low
- P03A1Cylinder 2 Pressure Sensor Circuit Low
Sources
- saabwisonline.com: dtc p0397 p0398 p03a1 p03a2 p03ab p03ac p03b5 or p
- law.cornell.edu: 13 CCR 1968.2
- borgwarner.com: pressure sensor glow plugs
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.