Cracked or disconnected vacuum hose, especially at the intake manifold or PCV system.; Leaking intake manifold gasket or throttle body gasket.; Damaged or loose intake air duct between the MAF sensor and throttle body.; Faulty positive crankcase ventilation (PCV) valve or hose.; Leaking brake booster hose or check valve.; Loose or missing oil dipstick or oil filler cap (on some engines).; Cracked intake manifold or vacuum reservoir.

DTC codes / P22xx · Fuel and air metering (injector circuits) / P2279

P2279Intake Air System Leak

Q: What does code P2279 mean?

Intake Air System Leak. P2279 indicates that the engine control module (ECM) has detected an intake air system leak, meaning unmetered air is entering the engine after the mass air flow (MAF) sensor or the throttle body. The ECM typically sets this code when fuel trim values exceed a calibrated threshold, indicating the engine is running leaner than expected due to the extra air.

P2279 indicates that the engine control module (ECM) has detected an intake air system leak, meaning unmetered air is entering the engine after the mass air flow (MAF) sensor or the throttle body. The ECM typically sets this code when fuel trim values exceed a calibrated threshold, indicating the engine is running leaner than expected due to the extra air.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering (injector circuits)

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms.
Rough or erratic idle, sometimes with surging or stalling when coming to a stop.
Hesitation or stumble during acceleration, particularly at low speeds.
Whistling, hissing, or sucking noises from the engine bay while running.
Poor fuel economy or increased fuel consumption.
In some cases, a lean misfire code may accompany P2279.

Common causes, most likely first

Cracked or disconnected vacuum hose, especially at the intake manifold or PCV system.
Leaking intake manifold gasket or throttle body gasket.
Damaged or loose intake air duct between the MAF sensor and throttle body.
Faulty positive crankcase ventilation (PCV) valve or hose.
Leaking brake booster hose or check valve.
Loose or missing oil dipstick or oil filler cap (on some engines).
Cracked intake manifold or vacuum reservoir.

How to diagnose and fix it

Perform a visual inspection of all intake air ducts, vacuum hoses, and connections for cracks, looseness, or disconnection.
Use a smoke machine to introduce smoke into the intake system and locate the leak source.
Check the PCV system for proper operation and leaks, including the valve and hoses.
Inspect the brake booster hose and check valve for leaks or damage.
Verify that the oil dipstick and filler cap are properly seated and sealing.
If no external leak is found, perform a fuel trim and MAF sensor analysis to rule out sensor errors.
Repair or replace the leaking component and clear the code, then verify fuel trims return to normal.

Common Misdiagnosis Traps for P2279

A dirty or failing mass air flow sensor can mimic an intake leak by underreporting airflow, causing lean fuel trims and setting P2279 without any actual leak.
Leaks that only occur under certain conditions, such as cold engine or high vacuum, may not show up in a static smoke test and require dynamic testing.
The PCV system is a frequent culprit, but a stuck-open PCV valve can act like a controlled vacuum leak and is often overlooked during visual inspections.
On engines with a plastic intake manifold, hairline cracks near the throttle body or runner flanges can be invisible to the eye and only detected with a smoke machine.
P2279 can be set by a loose oil filler cap or dipstick on engines where the crankcase is part of the intake system, so always check the simple things first.

Can I keep driving with P2279?

It is generally safe to drive short distances to a repair shop, but avoid hard acceleration or heavy loads because a lean condition can cause misfires and overheating. Prolonged driving with an intake leak can damage the catalytic converter and oxygen sensors.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.