P2279
PowertrainIntake Air System Leak
The ECU has detected an air leak in the intake system between the air filter and the engine. Unmetered air is getting in somewhere that the MAF or MAP sensors can't account for, which throws off fuel mixture calculations.
ⓘ Information only. This page provides general educational information about fault code P2279. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P2279 mean?
P2279 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Intake Air System Leak.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light
- • Rough idle, particularly at low revs
- • Hesitation when accelerating
- • Worse fuel economy
- • Sometimes a faint hissing or whistling under the bonnet (the leak itself)
- • Possibly stalling at idle with the engine cold
- • On diesels: black smoke under load if the leak is severe
Possible causes
Causes commonly associated with P2279, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Split or perished intake hose between air filter and throttle body, the most common cause; rubber boots crack with age
- 2. Loose intake hose clamp, often after recent service work where the hose was disturbed
- 3. Cracked plastic intake manifold, common on older BMW and VAG cars where the plastic ages and brittles
- 4. Leaking PCV valve or hose (crankcase ventilation), part of the intake system
- 5. Brake servo vacuum hose split or disconnected
- 6. Failed intake manifold gasket on cars with replaceable gaskets
- 7. On turbo cars: split intercooler hose
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Visual inspect all visible intake hoses with the engine running, look for cracks, splits, oil residue at clamps, or hoses that have popped off entirely
- 2. Spray carb cleaner around suspect joints with the engine idling, an idle change confirms a leak (clean burns and changes the mixture briefly)
- 3. Smoke test the intake at workshop (£30-£60 at independent garage), this finds tiny leaks that visual inspection misses
- 4. Check the brake servo hose specifically, disconnecting it briefly should stall a healthy engine; if it doesn't, the servo or hose may be the leak
- 5. Inspect plastic intake components for cracks, particularly on older BMW (cylinder head crankcase vent) and VAG (intake manifold) engines
Common questions about P2279
Could a recent service have caused this? +
Very possibly. After spark plug, air filter, or intake-related work, hoses can be left loose, gaskets misaligned, or vacuum lines disconnected. If P2279 appeared shortly after a service, check the work area first; most post-service vacuum leaks are obvious once you know to look.
Will the car run if I just ignore it? +
Yes in the short term, but with worse fuel economy and possible misfires. Long-term, persistent vacuum leaks cause sustained lean running which damages oxygen sensors and the catalytic converter. Fix within a couple of weeks rather than months.
I can hear hissing, where do I look? +
With the engine running and bonnet up, listen carefully near the intake manifold and brake servo area. Sometimes a stethoscope (£15) helps localise it. The hissing usually changes with engine speed and load. A torch under the bonnet at night sometimes shows fine cracks in plastic intake parts.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →