What it means
The ECM detects that crankcase ventilation hose B is disconnected based on pressure or vacuum signals. Unmetered air ingress and oil mist escape are possible.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Crankcase ventilation hose B carries blow-by gases between the crankcase and the engine’s ventilation or intake system. The control module infers that hose B is disconnected from pressure or vacuum behavior; a loose or split hose can admit unmetered air and release oil vapour.
Common causes
Most likely first.
- Hose disconnected at fitting
- Hose split or perforated
Symptoms
- Check-engine light
- Rough or uneven idle
- Hissing or whistling from the engine bay
- Oil smell or visible oily residue near the hose
How to diagnose it
- Review freeze-frame data and idle or fuel-trim readings to see whether the fault appeared under conditions that make a hose B leak more apparent.
- With the engine off and cool, identify hose B from the vehicle’s routing information and check whether its ends are seated on their fittings.
- Inspect the entire length of hose B for cracks, perforations, collapsed areas, or oily residue indicating escaping vapour.
- Listen near hose B for hissing or whistling with the engine idling, keeping clear of hot and moving components.
- If hose B appears intact, check its fittings and ventilation passage for leakage or blockage using the manufacturer’s diagnostic procedure.
Common fixes
- Reconnect hose B securely at the loose fitting.
- Replace a split or perforated crankcase ventilation hose B.
- Repair or replace a damaged hose B fitting or retaining clip.
- Clear the code and verify stable idle and normal ventilation operation.
Can I keep driving?
A leak at hose B can cause rough idle and allow unmetered air into the engine, so avoid unnecessary driving and high loads until repaired. Stop if the engine runs severely unevenly or fumes enter the cabin.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.