OBD-II code · Powertrain (generic)
P03B9 Cylinder 4 Pressure Too High
Cylinder 4 measured peak combustion pressure is above the calibrated maximum — typically pre-ignition, knock, over-fuelling, or runaway combustion.
Is it safe to drive with P03B9?
The car may go into limp mode (reduced power). Get it diagnosed before a long trip.
Common causes
- Most likelyPre-ignition or knock
Repair at a glance
- Difficulty
- Hard
- DIY friendly
- Best left to a mechanic
- Typical labour
- 2–8 h
- Emissions test
- Likely to fail
- Parts involved
- Cylinder Pressure Sensor
Related codes
- P039BCylinder 1 Pressure Too High
- P03A5Cylinder 2 Pressure Too High
- P03AFCylinder 3 Pressure Too High
- P03B3Cylinder 4 Pressure Sensor Circuit
- P03C3Cylinder 5 Pressure Too High
- P03CDCylinder 6 Pressure Too High
- P03D7Cylinder 7 Pressure Too High
- P03E1Cylinder 8 Pressure Too High
- P234ECylinder 9 Pressure Too High
- P2358Cylinder 10 Pressure Too High
- P236CCylinder 12 Pressure Too High
- P03B6Cylinder 4 Pressure Sensor Circuit High
- P03B7Cylinder 4 Pressure Sensor Circuit Intermittent/Erratic
- P03B8Cylinder 4 Pressure Too Low
- P03BACylinder 4 Pressure Variation Low
- P03BBCylinder 4 Pressure Variation High
- P03BCCylinder 4 Combustion Performance
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.