P2279: Intake Air System Leak
Quick Answer
Safe to drive (short-term)
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.
- Severity
- Moderate · Emissions
- Estimated repair cost
- From €8 to €750+, varies by vehicle
€8 or €750, depending on your car.
- Replace a missing or damaged oil filler cap€8–€50
- Replace intake manifold gasket€290–€750
A scan shows whether P2279 is really stored on your car, which codes sit next to it and how urgent each one is.
A scan needs a Bluetooth OBD2 adapter (Bluetooth LE on iPhone), about €25-60; the built-in demo runs without one. See which adapter to buy
What does P2279 mean?
P2279 is a emissions-related diagnostic trouble code classified as moderate severity.
Where it is on the car
- Air filter box
- Mass airflow sensor (MAF)
- Throttle body and throttle position sensor
- Intake manifold and MAP sensor
- Engine (cylinder head)
A lean code usually means extra air is getting in after the MAF sensor, for example through a leaking intake hose, a cracked vacuum line or a worn manifold gasket. The intake manifold side is the first place to look. A dirty MAF sensor that reads too little air is the other common cause.
What are the symptoms of P2279?
- 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
What causes P2279?
Cracked or split intake boot between MAF and throttle body
: high
Failed PCV valve, torn PCV diaphragm, or split PCV hose
: high
Leaking intake manifold gasket, common on aged plastic manifolds
: medium
Cracked vacuum line or perished brake booster hose
: medium
Leaking throttle body gasket after a cleaning or reinstall
: low
Missing, cross-threaded, or torn-gasket oil filler cap
: low
Is it safe to drive with P2279?
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.
How do you diagnose P2279?
- Scan for all stored codes. P2279 usually shows up with P0171 and/or P0174, which confirm the lean condition.
- Read live fuel trims at idle and at 2500 rpm. Long-term trim strongly positive at idle but close to zero at higher rpm points to a small vacuum leak, because a fixed amount of unmetered air matters far less once total airflow rises.
- Visually inspect the intake boot, flexing it and checking the underside where cracks often hide, plus the clamps at the MAF and throttle body.
- Pull the oil filler cap at idle. If idle changes sharply or the cap sucks down hard, the PCV system needs attention.
- Smoke test the intake tract with an EVAP smoke machine at 0.5 psi (0.035 bar). Escaping smoke pinpoints the leak in minutes.
- With the engine idling, spray carb cleaner or feed propane around suspect joints. An rpm change confirms leak location.
- Inspect intake manifold seams, vacuum ports, and the brake booster hose for cracks, especially on plastic manifolds past 150,000 km.
- Clear the code, drive a full warm-up cycle, and recheck fuel trims to confirm the repair took.
How much does P2279 cost to fix?
| Repair | Parts Cost | Labor Cost | Total Estimate | DIY Difficulty |
|---|---|---|---|---|
| Replace cracked intake boot or hose | €25–€90 | €30–€80 | €55–€170 | Easy |
| Replace PCV valve and associated hoses | €15–€120 | €40–€150 | €55–€270 | Easy |
| Replace intake manifold gasket | €40–€150 | €250–€600 | €290–€750 | Professional |
| Replace vacuum lines or brake booster hose | €10–€60 | €40–€120 | €50–€180 | Easy |
| Replace throttle body gasket | €15–€50 | €80–€180 | €95–€230 | Moderate |
| Replace a missing or damaged oil filler cap | €8–€30 | €0–€20 | €8–€50 | Easy |
Prices estimated as of October 2026. Costs vary by region, vehicle, and shop.
P2279 on specific vehicles
Ford
Ford F-150 5.4L Triton 3V
2004-2010
The 5.4L 3V is well documented for split PCV hose elbows and cracked plastic intake manifolds around the coolant crossover.
Volkswagen
Volkswagen Golf 2.0 TSI (EA888 Gen 2)
2008-2014
The EA888 Gen 2 valve cover integrates the PCV diaphragm. When it tears (very common past 100,000 km) you get a huge vacuum leak and instant lean codes. Full valve cover replacement is the fix.
BMW
BMW 3-Series N54/N55 (E90/E92)
2007-2013
N54 plastic charge pipes crack at the throttle body flange, especially with a tuned car. N55 valve cover CCV/oil separators fail and pull crankcase vacuum into the intake.
Toyota
Toyota Camry 2.4L 2AZ-FE
2002-2009
The 2AZ-FE is generally leak-tight, but the ribbed intake air connector between MAF and throttle body hardens and splits along the convolutions past 200,000 km.
Honda
Honda Civic 1.8L R18A
2006-2011
R18 owners commonly find the PCV hose to the intake manifold hardens and cracks at the fitting. The IMRC gasket on the lower intake also leaks by 150,000 km.
Related diagnostic codes
Common questions about P2279
- Can I tape up a cracked intake boot to get home?
- Self-fusing silicone tape will hold for a day or two, but the crack keeps propagating with every vacuum pulse. A replacement boot is 25 to 90 euros and usually a 20 minute job with a screwdriver.
- Why does my car idle rough but drive perfectly fine on the motorway?
- Manifold vacuum is highest at idle when total airflow is lowest, so a pinhole leak makes up a big percentage of the air the engine sees. At cruise the same leak is a rounding error and closed-loop trims mask it.
- Will P2279 damage anything if I keep driving?
- The engine won't self-destruct, but sustained lean running raises combustion temps and cooks the catalytic converter over weeks. A new cat is 400 to 1500 euros, so spending 50 euros on a hose is the smart play.
- Can a dirty MAF sensor cause P2279 on its own?
- No. P2279 specifically flags air the MAF never saw. A contaminated MAF typically sets P0101 or generic lean codes. Clean it with dedicated MAF spray if it looks oily, but don't stop looking after that.
- Does a loose oil cap actually trigger P2279?
- On many engines, yes. The oil cap seals the PCV circuit. If it's missing, cross-threaded, or the rubber seal is flat, you pull unmetered air straight into the crankcase and into the intake.