P2279: Intake air system leak
The engine computer has found air getting into the intake that the air flow (MAF) sensor didn’t measure: a leak somewhere between the sensor and the engine.
Updated
What P2279 means
The air flow (MAF) sensor measures the air the engine draws in, and the engine computer injects fuel to match. Air that gets in after the sensor isn’t measured, so the mixture runs lean.
P2279 means the engine computer has found signs of such a leak, by comparing the air it measures with what it expects. It’s closely related to P0171 (system too lean), and the two often come together.
Read My Car shows fuel trim under Live data, if your car reports it. A leak usually shows as high positive values at idle that get smaller at higher engine speeds.
Can I keep driving?
Drive gently
Avoid hard driving and have it checked soon. The leak makes the engine run lean, which can make it misfire or stall and, under heavy load, damage the engine or the catalytic converter. If the engine stalls, runs very rough or the check engine light flashes, stop when it’s safe to do so.
General guidance based on the code alone, not on the car’s actual condition. If in doubt, stop and ask a mechanic.
A lean engine can misfire, hesitate or stall, especially at idle. Misfire codes (P0300 to P0312) stored at the same time make it more urgent.
Symptoms
- A rough or uneven idle.
- A hissing noise from the engine bay on some cars.
- Hesitation or stalling.
- Lean or misfire codes stored at the same time.
Common causes
- Split or loose intake hose or duct after the air flow sensor. Check the ducting and its clamps all the way from the sensor to the engine, and the seal around the sensor itself.
- Leaking vacuum hose. Rubber hoses harden and crack with heat and age, for example the hose to the brake servo.
- Faulty PCV valve or hose. The crankcase ventilation (PCV) system vents into the intake. A faulty valve or a cracked hose lets in unmeasured air.
- Leaking intake manifold or throttle body gasket. Gaskets harden with age and can let air in.
Typical fixes
- Check the air filter housing, the sensor’s seal and the ducting to the engine for splits and loose clamps.
- Listen for hissing with the engine idling, and check the vacuum hoses and the PCV (crankcase ventilation) system.
- Have a smoke test done if nothing is found: it shows leaks that are hard to see.
- Clear the code after the repair, and check in live data that fuel trim moves back towards zero.
Questions
Can I drive with P2279?
Gently, and have it checked soon. A lean engine can misfire or stall and, under heavy load, damage the engine or catalytic converter. If it stalls, runs very rough or the check engine light flashes, stop when it’s safe to do so.
What is the difference between P2279 and P0171?
P0171 says the mixture is too lean, for any reason. P2279 says the engine computer suspects an air leak in the intake specifically. A leak often sets both.