P234D
Cylinder 9 Pressure Too Low
Cylinder 9 measured peak combustion pressure is below the calibrated minimum — typically low compression, weak injection, or stuck-open exhaust valve.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: hard
Common causes
Ordered by how often each turns out to be the cause.
- Low compression on cylinder 9 (valves, rings, head gasket)Common
- Injector flow too lowPossible
Parts involved
- Cylinder 9 Combustion
- Cylinder Compression
- Fuel Injector Cyl 9
P234D 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.