P04DBCrankcase Ventilation System Disconnected
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- The crankcase ventilation (PCV) system routes blow-by gas from the crankcase into the intake; CARB requires a disconnection between crankcase and intake to be detected. GM's 2.0-litre LSY has a pressure sensor in the PCV hose: with the hose connected it must see a pressure drop that grows with air flow, plus pressure pulses from the pistons. Ford reports the same sensor type as crankcase pressure sensor A (P051A ff). P04DB means a disconnection: without the pressure drop the clean-air side is off, without the pulses the crankcase side. GM's LSY uses the product of normalised offset and noise (below 0.63 kPa², MIL after two trips); Ford's EcoBoost checks the dirty side at cranking and the clean side above 5 lb/min of air. Engines without such a sensor may report a disconnection through mixture or load codes, as CARB allows. FCA bulletins cover it on the Alfa Romeo 2.0 turbo and the Ram 3.0 EcoDiesel.
- What you may notice
- Check engine light on
- Hissing, false air, rough idle or lean running
- Oil mist or smell in the engine bay
- Likely causes
- LikelyVentilation hose off or quick connector not latched (often after intake work)
- LikelyHose cracked or porous, or nipple broken
- PossiblePCV valve stuck closed or oil separator blocked or frozen (simulates a disconnection)
- RarePressure sensor in the hose giving a wrong signal
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €0 – €200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.