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.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: hard
Common causes
Ordered by how often each turns out to be the cause.
- Pre-ignition or knockCommon
Parts involved
- Cylinder Pressure Sensor
P03B9 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.