P2279: Intake Air System Leak

P2279 means the ECU sees more air in the cylinders than the MAF measured, so unmetered air is entering downstream of the sensor and pushing fuel trims positive.

P2279 is a emissions-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P2279 and illuminates the check engine light.

If your vehicle has triggered P2279, you may notice one or more of these symptoms:

• Rough or unstable idle, sometimes stalling when coming to a stop
• Hissing or whistling from the intake area, loudest at idle
• Long-term fuel trims above +10% at idle, dropping closer to zero at 2500 rpm
• Fuel economy down 5 to 15% over a tank
• Hesitation or stumble on light tip-in from a stop
• Companion lean codes P0171 and/or P0174 stored with P2279

Here are the most common causes of P2279, ranked by how likely they are to be the culprit:

Generally yes, for short-term driving. You can drive short distances, but rough idle and lean running can overheat the catalytic converter and trigger misfires. Fix it within a week or two.

Follow these steps to pinpoint the root cause of P2279:

1. Scan for all stored codes. P2279 usually shows up with P0171 and/or P0174, which confirm the lean condition.
2. Read live fuel trims at idle and at 2500 rpm. Strongly positive STFT at idle that normalizes at higher rpm points to a small vacuum leak.
3. Visually inspect the intake boot, flexing it and checking the underside where cracks often hide, plus the clamps at the MAF and throttle body.
4. Pull the oil filler cap at idle. If idle changes sharply or the cap sucks down hard, the PCV system needs attention.
5. Smoke test the intake tract with an EVAP smoke machine at 0.5 psi. Escaping smoke pinpoints the leak in minutes.
6. With the engine idling, spray carb cleaner or feed propane around suspect joints. An rpm change confirms leak location.
7. Inspect intake manifold seams, vacuum ports, and the brake booster hose for cracks, especially on plastic manifolds past 150,000 km.
8. Clear the code, drive a full warm-up cycle, and recheck fuel trims to confirm the repair took.

Repair costs for P2279 vary depending on the root cause and your vehicle. Here are typical estimates:

P2279 behaves differently depending on your vehicle. Select your car below for model-specific causes, known issues, and adjusted cost estimates:

These codes are often seen alongside P2279 or indicate related issues: