P04DB
Crankcase Ventilation System Disconnected
A pressure or flow sensor in the crankcase ventilation (PCV) circuit reports atmospheric conditions where it should see crankcase or intake vacuum - the hose between crankcase and intake is disconnected, cracked, or open. PCV no longer routes blow-by gases into the intake, increasing oil mist emissions and risking oil leaks.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: easy
Common causes
Ordered by how often each turns out to be the cause.
- PCV hose pulled off or splitCommon
- Oil filler cap missing or loosePossible
Parts involved
- PCV Hose
- PCV Valve
- PCV Sensor
P04DB 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.