P04DB

What it means

P04DB is the generic code for the crankcase ventilation system being disconnected. The engine control unit monitors the breather line between the crankcase and the intake, and it has seen a pressure or flow change that suggests the line has come apart or is leaking. The exact monitoring method, such as a pressure sensor or a fuel trim and airflow comparison, depends on the make and engine.

Symptoms

• Engine warning light on
• Rough or unstable idle
• Whistling, hissing or sucking noise from the engine bay
• Oil leaks or oil mist around the breather hose, dipstick or filler cap
• Lean running or fuel trim related faults stored alongside
• Increased oil consumption

Possible causes

• Crankcase breather hose or pipe has come off its connector or is crackedlikely
• Perished or damaged breather hose seals, quick-release connectors or O-ringslikely
• Oil filler cap missing, loose or sealing poorly, or dipstick not seatedpossible
• Damaged or blocked oil separator or breather housing, including a split diaphragmpossible
• Faulty crankcase pressure sensor or its wiring and connector, on engines that have onepossible
• Excessive blow-by from engine wear overwhelming the system and causing a false disconnect readingrare

How to diagnose

1. Read the stored codes and freeze frame data, noting any fuel trim, misfire or airflow faults stored with it.
2. Check the oil filler cap, its seal and the dipstick are fitted correctly and undamaged.
3. Visually inspect the whole breather line from the crankcase to the intake, checking each connection is fully seated and locked.
4. Look for cracks, softening, heat damage or oil-soaked hoses, and check the connector seals and O-rings.
5. Inspect the oil separator or breather housing for damage, blockage or oil sludge, following the procedure for that engine.
6. With the engine idling, listen for air leaks and check for changes in idle when a suspect hose is moved.
7. If the engine has a crankcase pressure sensor, inspect its connector and wiring and check its readings against the manufacturer's specification.
8. Check for signs of excessive blow-by, such as heavy oil mist at the filler, if no other fault is found.

How to fix

• Reconnect and secure the breather hose, replacing any retaining clip or locking connector that is damaged.
• Replace cracked, perished or oil-soaked hoses, along with their seals or O-rings.
• Fit a correct, undamaged oil filler cap and seat the dipstick properly.
• Replace a faulty oil separator or breather housing.
• Repair wiring or the connector, or replace the crankcase pressure sensor if it is proven faulty.
• Address underlying engine wear if excessive blow-by is confirmed.

Can I keep driving?

Nearby codes

• P04DAGenericClosed Loop EGR Control At Limit - Flow Too High
• P04DCGenericFuel Fill Door Position Sensor/Switch Circuit Range/Performance