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. GM's European 2.0 CDTI diesel (Saab 9-5, 2010) uses P03B1 as 'pressure variation too high' and sets it when the signal is outside its range for more than 0.2 s with the engine running; its fault table counts it among the signal performance faults together with the erratic code. What exactly is measured, Saab does not explain; presumably it is the swing of the pressure signal within an engine cycle – too large a swing points to a noisy or overshooting signal or implausible pressure peaks, for example from faulty sensor electronics, interference on the signal wire or, less often, a combustion anomaly such as a dripping injector. Usually there are no noticeable symptoms.
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
- Usually no noticeable symptoms
- Possibly rough running or combustion noise because control is off
Most likely causes
- Sensor in the glow plug faulty (signal noise)
- Loose contact or interference on the signal wire
- Combustion anomaly (dripping injector, harsh combustion)
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 P03B1 means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- 3: Ignition and misfires
- B1: Specific fault in that system
Frequently asked questions
Can I keep driving with code P03B1?
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 P03B1?
The most common causes are: sensor in the glow plug faulty (signal noise); loose contact or interference on the signal wire; combustion anomaly (dripping injector, harsh combustion).
Related codes
- P03B0Cylinder 3 Pressure Variation Low
- P03ADCylinder 3 Pressure Sensor Circuit Intermittent/Erratic
- P03AACylinder 3 Pressure Sensor Circuit Range/Performance
- P039DCylinder 1 Pressure Variation High
- P03A7Cylinder 2 Pressure Variation High
Sources
- saabwisonline.com: dtc p0399 p039c p039d p03a3 p03a6 p03a7 p03ad p03b
- patents.google.com: US7726281
- law.cornell.edu: 13 CCR 1968.2
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.