What it means
The ECM detects that crankcase ventilation hose A 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 A carries blow-by gases from the engine crankcase into the intake or ventilation system. The control module infers that hose A is disconnected from pressure or vacuum behavior; an open hose can admit unmetered air and let oil vapour escape.
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
- Check freeze-frame data and fuel-trim or idle data to see whether the fault occurred at idle, when an air leak through hose A is most noticeable.
- With the engine off and cool, locate hose A using the vehicle’s routing information and check whether either end has come off its fitting.
- Inspect the full length of hose A for splits, soft spots, collapsed sections, and oily residue that can mark a leak.
- Listen for hissing or whistling around hose A while the engine idles, keeping hands and clothing clear of moving or hot parts.
- If the hose looks intact, check its connections and ventilation passage for blockage or leaks using the manufacturer’s diagnostic procedure.
Common fixes
- Reconnect hose A firmly at its fitting.
- Replace a split or perforated crankcase ventilation hose A.
- Repair or replace a damaged hose A connector or retaining clip.
- Clear the code and confirm that idle quality and ventilation readings return to normal.
Can I keep driving?
A disconnected hose A can cause rough running and unmetered air entry, so limit driving and avoid high engine loads until it is reconnected or repaired. Stop if the engine runs very poorly or oil vapour or fumes are entering 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.