P2279: Intake Air System Leak
Severity: medium
What it means: The engine computer sees more air getting into the engine than the airflow sensor measured. That usually means unmetered air is leaking in somewhere after the sensor, such as a cracked hose, a bad intake gasket or a failed PCV valve (the crankcase breather valve).
Safe to drive? Usually yes for short trips, but get it fixed soon. A large leak can cause stalling, a rough idle and lean running, which can damage the engine over time.
Common symptoms
- Check-engine light with P2279
- Rough, bouncing or high idle
- Whistling or hissing from the engine bay
- Often set along with P0171 (running lean) or P0507 (idle too high)
Likely causes, ranked
- Failed PCV valve or oil separatorDIY or shop
- Cracked or loose vacuum or intake hoseDIY
- Leaking intake manifold gasketShop
- Faulty airflow (MAF) sensor readingDIY or shop
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Vehicle-specific notes
- :
DIY or shop?
Checking hoses and the oil cap is DIY. A smoke test (pumping visible smoke into the intake to show leaks) is quick shop work and finds most leaks.
Before you replace parts
- With the engine warm and idling, listen for a whistle or hiss.
- Try to lift the oil filler cap. If it is sucked down hard, suspect the PCV valve.
- Look over the intake hoses and boots for cracks or loose clamps.
- If nothing obvious turns up, get a smoke test before buying parts.
Vehicle notes
- Audi A4 2.0T (2009–2016 B8): a torn PCV / oil separator diaphragm is the classic cause, often with a whistle and the oil cap sucked down at idle. See the related A4 answer.
Sources
Safety / mechanic note
A code points to a system, not always a specific part. Verify with a mechanic before replacing expensive parts.
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