OBD-II code · Powertrain (generic)
P03B8 Cylinder 4 Pressure Too Low
Cylinder 4 measured peak combustion pressure is below the calibrated minimum — typically low compression, weak injection, or stuck-open exhaust valve.
Is it safe to drive with P03B8?
Usually safe for short trips, but don’t ignore it: the underlying fault can get more expensive over time.
Common causes
- Most likelyLow compression on cylinder 4
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
- P039ACylinder 1 Pressure Too Low
- P03A4Cylinder 2 Pressure Too Low
- P03AECylinder 3 Pressure Too Low
- P03B3Cylinder 4 Pressure Sensor Circuit
- P03C2Cylinder 5 Pressure Too Low
- P03CCCylinder 6 Pressure Too Low
- P03D6Cylinder 7 Pressure Too Low
- P03E0Cylinder 8 Pressure Too Low
- P234DCylinder 9 Pressure Too Low
- P2357Cylinder 10 Pressure Too Low
- P2361Cylinder 11 Pressure Too Low
- P236BCylinder 12 Pressure Too Low
- P03B5Cylinder 4 Pressure Sensor Circuit Low
- P03B6Cylinder 4 Pressure Sensor Circuit High
- P03B7Cylinder 4 Pressure Sensor Circuit Intermittent/Erratic
- P03B9Cylinder 4 Pressure Too High
- P03BACylinder 4 Pressure Variation Low
- P03BBCylinder 4 Pressure Variation High
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.