P2279
Leak in Air Intake SystemP2279 is a generic OBD-II powertrain diagnostic trouble code: Leak in Air Intake System. It is logged by the engine control unit when the scr/adblue monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P2279 means
Code P2279 is triggered when the ECU detects unmetered air entering the intake tract downstream of the mass air flow (MAF) sensor — commonly called a vacuum or boost leak. The MAF sensor measures the volume of air entering the engine, and the ECU calculates the correct fuel quantity based on that reading. When additional air enters the system through a crack, failed gasket, loose hose, or defective component, the actual air-fuel mixture is leaner than the ECU's model predicts. To compensate, the ECU increases fuel delivery (positive fuel trim correction), and when the correction exceeds a calibrated threshold, P2279 is set.
The intake system on a modern engine is an intricate network of hoses, gaskets, solenoid ports, and plastic manifold sections spanning from the air filter box to each intake port. Common failure points include the intake manifold gasket (which cracks or shrinks with age, especially on aluminium manifolds subject to thermal cycling), the throttle body O-ring, brake booster vacuum line, PCV system hoses, and intercooler couplings on turbocharged vehicles. Even a small crack in a rubber elbow between the MAF sensor and throttle body is sufficient to set the code.
On turbocharged and supercharged engines P2279 is particularly significant because a boost-side leak not only biases the MAF reading but also directly reduces available charge pressure, degrading performance noticeably. Naturally aspirated engines often show primarily rough idle and lean surge at low load, with performance near normal under wide-open throttle where manifold vacuum is low.
P2279 is closely related to generic lean codes such as P0171 (Bank 1 lean) and often appears alongside them.
Common causes
Most-frequently reported root causes when P2279 is logged.
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1
Cracked, disconnected, or collapsed air intake hose between MAF and throttle body (most common)
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2
Failed or shrunken intake manifold gasket
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3
Damaged throttle body O-ring or gasket
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4
Disconnected or cracked vacuum hose (brake booster, MAP sensor, idle control)
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5
Leaking PCV system hose or valve
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6
Cracked intercooler coupling or loose boost pipe clamp (turbocharged engines)
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7
Faulty or contaminated MAF sensor reporting lower airflow than actual
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8
Failed fuel injector O-ring allowing air ingestion at injector seat
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9
Defective brake booster diaphragm pulling additional unmetered vacuum
Symptoms drivers notice
How to diagnose P2279
A typical diagnostic flow when this code is present.
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1
Connect a scan tool and check for companion lean codes (P0171/P0174) and live fuel trim data — LTFT values above +10% strongly support a significant air leak
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2
With engine idling, listen carefully for a hissing or whistling sound; trace systematically from the air filter housing along every hose and joint to the throttle body
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3
Visually inspect all intake hoses, couplings, intercooler pipes (on turbo engines), and vacuum lines for cracks, tears, loose clamps, or disconnections
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4
Perform a smoke test (EVAP/intake smoke machine): introduce smoke into the intake system at the throttle body with the engine off and all downstream ports sealed; smoke escaping from any joint, gasket face, or hose confirms the leak location
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5
Alternatively, use a propane enrichment test: with the engine idling, direct a small flow of propane gas around suspected leak points — a sudden increase in idle speed or RPM indicates the leak source
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6
Check MAF sensor readings at idle and compare to specification; a contaminated MAF under-reporting airflow can mimic a lean condition — inspect and clean the MAF element if necessary
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7
Repair confirmed leaks (replace hose, tighten clamp, renew gasket/O-ring), clear codes, and verify fuel trims return within ±5% after a normalising drive cycle
Related powertrain codes
- B0001 — PCM Discrete Input Speed Signal Error
- B0004 — PCM Discrete Input Speed Signal Not Present
- C0359 — Four Wheel Drive Low Range (4LO) Discrete Output Circuit
- C0362 — 4LO Discrete Output Circuit High
- P2000 — NOx Adsorber Efficiency Below Threshold Bank 1
- P2001 — NOx Adsorber Efficiency Below Threshold Bank 2
Frequently asked questions
Is P2279 the same as a vacuum leak?
Effectively yes. P2279 describes unmetered air entering the intake downstream of the MAF sensor, which is the definition of a vacuum (or boost) leak.
Can a dirty MAF sensor cause P2279?
Yes. A contaminated MAF element under-reports airflow, causing the ECU to add fuel (positive trim).
How do I find an intake leak without a smoke machine?
The propane enrichment method is the most reliable low-cost alternative.
Will P2279 damage the engine if left unrepaired?
Prolonged lean operation can cause detonation under load, increasing the risk of piston, valve, and catalyst damage.
Can P2279 appear after engine work or an air filter change?
Yes. An intake hose reconnected incorrectly, a clamp not fully tightened, or an air filter housing seated improperly after a service are common triggers.
Disabling P2279 in software
RaceTune can permanently disable P2279 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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