OBD codes / P2279
P2279
ModerateIntake Air System Leak
Generally safe to drive short-term — the engine runs lean and may idle high or rough, but it won't typically strand you. Don't ignore it for months: sustained lean running is hard on the engine and catalytic converter, and the erratic idle can worsen. Schedule a smoke test soon.
What this code means
P2279 means the computer has detected air entering the engine that didn't come through the throttle body as expected — unmetered air leaking into the intake downstream of the throttle plate. The engine's airflow, manifold pressure, and throttle position readings stop adding up, and on many vehicles the idle rises or hunts because the computer can't fully control airflow with the throttle. Typical sources are leaking intake manifold gaskets, cracked or disconnected PCV hoses and vacuum lines, a leaking brake booster hose, a loose oil filler cap or dipstick seal, and torn intake boots or elbow couplers. Because the extra air also leans out the mixture, P2279 frequently appears alongside lean codes (P0171/P0174) or high-idle codes (P0507). A smoke test of the intake is the fastest way to pinpoint the leak; guessing at hoses wastes money.
Symptoms you might notice
- High, hunting, or unstable idle
- Hissing or whistling noise from the engine bay
- Hesitation or rough running, especially at idle and low speed
- Often paired with lean codes (P0171/P0174) or P0507
- Check-engine light
What it costs to fix
Typical range: $40–$600 · about ~0.3–3 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| Vacuum / PCV hose replacement | $5–$80 | ~0.3–1 hrs |
| Intake manifold gasket | $20–$150 | ~1–3 hrs |
| Smoke test / diagnosis | $0–$0 | ~0.5–1 hrs |
Cost is almost entirely about where the leak is. A brittle vacuum hose or loose oil cap is nearly free; an intake manifold gasket buried under other components is a real labor job. Pay for the smoke test first — it turns guesswork into a targeted repair.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P2279 for my exact vehicle →
Frequently asked
What exactly is leaking with P2279?
Air is leaking IN, not fluid leaking out. Somewhere after the throttle plate — a gasket, hose, seal, or boot — outside air is sneaking into the intake without being measured, which throws off the fuel mixture and idle control.
How do I find the leak causing P2279?
A smoke test is the standard method: a machine fills the intake with visible smoke and the leak reveals itself. It beats spraying carb cleaner around a running engine, and it finds small leaks in hidden gaskets that eyeballing hoses will miss.
Why do I have P2279 together with P0171 or P0507?
One leak, multiple symptoms. Unmetered air leans out the mixture (P0171/P0174) and raises idle beyond the computer's control (P0507). Fixing the single leak usually clears all of the related codes at once.
Can a loose oil cap really cause P2279?
Yes — on many engines the crankcase connects to the intake through the PCV system, so a loose oil filler cap or a worn dipstick seal is an intake leak. It's one of the first, cheapest things to check before deeper diagnosis.
Seeing P2279 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P2279 for my vehicleRelated trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P2279 from your phone — see our honest guide to the best OBD2 Bluetooth adapters.
Generic OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.