P2279 code: Intake Air System Leak
P2279 means intake Air System Leak. The code says where to look, not what failed — the fix depends on which cause your car actually has.
What P2279 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.
P2279 symptoms
- 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 P2279
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 →
How to fix P2279
Moderate — doable at home with common tools and patience
- Check the oil cap, dipstick, and any recent intake work
Make sure the oil filler cap is tight with an intact seal and the dipstick seats fully on a good O-ring — both are part of the sealed intake path on most engines. Then think back: P2279 often appears right after plugs, coils, or a throttle body cleaning, when a hose was left off or a gasket was reused.
- Read throttle and airflow behavior at idle
On live data, compare throttle opening, airflow or manifold pressure, and fuel trims at warm idle. A leak usually makes the computer close the throttle further than normal to hold idle speed, while trims run positive and, on engines that rely on manifold pressure, vacuum reads weaker than expected.
- Smoke the intake from the throttle onward
Feed smoke into the intake behind the throttle body with the engine off and watch every joint downstream: manifold and throttle body gaskets, PCV and vacuum lines, the brake booster hose, injector seals, EGR fittings, and any coupler between throttle and manifold. Smoke shows the leak; guessing usually replaces hoses that weren't leaking.
- Repair the leak with fresh seals and correct torque
Replace a cracked hose with a properly sized one, and if one aged rubber hose has split, check its neighbors too. For gaskets, fit new ones rather than reusing old seals, and tighten manifold or throttle body bolts in the specified sequence and to spec so the new seal clamps evenly.
- Run the idle relearn and confirm
After the repair, many engines need an idle or throttle relearn, done with a scan tool or a key-and-idle procedure from the service manual. Then clear the code and confirm the throttle opening at idle, the trims, and idle speed have all returned to normal over a couple of drives.
DIY or shop? Many P2279 repairs are home-mechanic work: a cap seal, a dipstick O-ring, a vacuum line, or a PCV hose. The smoke test is the step most people lack equipment for, and it is worth having done if the obvious checks come up empty — it turns guessing into one targeted fix. Intake manifold gaskets are where it becomes a shop decision, since the job can involve removing fuel rails, coils, and wiring, followed by the idle relearn.
Tools for the DIY steps: Scan tool with live data · Smoke machine · Torque wrench · Replacement vacuum or PCV hose · Flashlight
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P2279.
Start a case with P2279 and your car. Redline weighs these causes against what your car shows, and names the check that would settle it before you buy parts.
Can I drive with P2279?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
P2279: common questions
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?
It does — 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.
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P2279 from your phone. See our guide to the best OBD2 Bluetooth adapters. Run a repair shop? See Redline for shops.
Generic OBD-II reference. Manufacturer-specific behavior varies. Confirm with a scan tool and, for safety-related codes, a professional inspection. Cost ranges are reference ranges, not quotes.
Seeing P2279 on your car?
Every problem becomes a Case. Tell Redline what the car is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.