Powertrain, generic · Auxiliary emission controls

P04DB Crankcase Ventilation System Disconnected

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

Ventilation hose off or quick connector not latched (often after intake work)
Hose cracked or porous, or nipple broken
PCV valve stuck closed or oil separator blocked or frozen (simulates a disconnection)
Pressure sensor in the hose giving a wrong signal

Symptoms

  • Check engine light on
  • Hissing, false air, rough idle or lean running
  • Oil mist or smell in the engine bay

Repair estimate

DifficultyEasyDIY possible
Parts and labour€0–200
Time0.2–1.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

crankcase ventilation hosepcv valvecrankcase ventilation hose sensorengine control module

Related codes

P04FCP04E2P04E3P04FBP051BP2282

References: gsi.ext.gm.com, fordservicecontent.com, patents.google.com, patents.google.com.