P2279
Intake Air System Leak
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Code P2279 is a straightforward diagnostic code indicating that the engine's computer has detected an air leak in the intake system. This means unmetered air — air that hasn't been measured by the mass airflow sensor — is entering the engine. The computer relies on knowing exactly how much air is entering the engine so it can inject the right amount of fuel. When extra air sneaks in through a leak, the air-fuel mixture goes lean and the engine runs poorly.
You'll likely notice a rough idle, possible stalling, and you may hear a hissing or whistling sound from the engine bay. The severity depends on the size of the leak — a small leak might just cause a slightly rough idle, while a large leak can make the engine stall repeatedly or run very poorly. Misfires are also common with intake leaks because the lean mixture in affected cylinders may not ignite properly.
This is one of the more DIY-friendly engine codes. Start by visually inspecting all vacuum hoses and the rubber intake duct for obvious cracks, loose connections, or disconnected hoses. Pay special attention to hoses near the back of the engine that are harder to see. A professional smoke test is the most reliable way to find intake leaks — a mechanic pumps smoke into the intake and watches for where it escapes. For a DIY approach, you can carefully spray carburetor cleaner around intake connections while the engine idles; a change in engine speed indicates you've found the leak.
Severity
Symptoms
- •Rough or unstable idle that may vary in severity
- •Engine stalling, especially at idle or deceleration
- •Hissing or whistling sound from the engine bay
- •Reduced power and poor acceleration
- •Check Engine Light on, possible misfires
Likely Causes
Rubber vacuum hoses become brittle with age and heat exposure, developing cracks or popping off their fittings. This is the most common and easiest-to-fix cause of an intake air leak.
The gasket between the intake manifold and cylinder head can deteriorate over time, allowing unmetered air to bypass the throttle body and enter the engine directly.
The flexible rubber duct connecting the air filter housing to the throttle body can develop tears or come loose from its clamps, allowing unfiltered and unmetered air into the engine.
A cracked PCV hose or a PCV valve stuck open allows excess crankcase air into the intake manifold, creating an unmetered air leak that the PCM cannot account for.
The rubber O-ring seals where fuel injectors sit in the intake manifold can shrink or crack with age, allowing air to leak into the intake port around the injector.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Inspect and replace cracked or disconnected vacuum hoses
- Replace the intake manifold gasket if leaking
- Tighten or replace the intake air duct/boot between the air filter and throttle body
- Replace the PCV valve and associated hoses
- Replace fuel injector O-ring seals if leaking
Shop Parts
Videos
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