P2279 – Intake air leak


By Reinier (Contact Me)
Last Updated 2018-10-02
Automobile Repair Shop Owner

Trouble CodeFault LocationProbable Cause
P2279 Intake air leak Mechanical fault

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What Does Code P2279 Mean?

OBD II fault code P2279 is a generic code that is defined as “Intake Air System Leak”, and is set when the PCM (Powertrain Control Module) detects a vacuum leak in the intake air system that allows unmetered air to enter the engine.

For a modern gasoline engine to function efficiently and to comply with current emissions regulations, the PCM on that engine needs to be able to both measure the volume of air that enters the engine very precisely, and then to match the volume of fuel it injects to that volume of air to produce an ideal air/fuel mixture.

For this reason, modern engine are fitted with MAF (Mass Airflow) sensors that measure the volume of air that flows past them, or, MAP (Manifold Absolute Pressure) sensors that measure the pressure in the intake manifold as a function of its volume. However, since the temperature of the intake air is directly related to its density, and hence its volume, modern engines are also fitted with IAT (Intake Air Temperature) sensors to monitor the temperature of the air that enters the engine.

Moreover, many engines are also fitted with barometric pressure sensors, whose function it is to measure the atmospheric pressure, since elevation above sea level is directly related to the density, and hence, the volume of air that enters the engine. In a fully functional intake system, the input data from all these sensors are combined by the PCM in various ways in order to arrive at a precise value for the volume of air that enters the engine, which value serves as the “foundation” upon which fuel delivery strategies are based.

Note though that other factors such as the engine speed, engine load based on the throttle position, and the engine coolant temperature, and input data from oxygen sensors in the exhaust system also feature in this equation, as does the PCM’s (limited) ability to compensate for the gradual loss of sensitivity in some implicated sensors. Thus, if all these inputs are taken together, and provided there are no exhaust leaks, misfires, or other mechanical issues present, the PCM is able to make the engine perform at its peak using the least amount of fuel, while producing the least amount of emissions at the same time.

In practice though, the PCM cannot monitor all the sites where unmetered air could possibly enter the engine, so when it detects (based on inputs from the previously mentioned sensors) that more air enters the engine than is reported by all implicated sensor inputs, it deduces that a leak exists in the intake air system. When this happens, the PCM also recognizes that it cannot control the air/fuel mixture effectively, and it will set code P2279, and depending on the severity of the leak, it may illuminate a warning light as well.

Where is the P2279 sensor located?

The image above shows one typical example of a leak in the intake air system that would produce code P2279. Note though that while this type of failure is obvious there are many possible sites where air could enter the engine, some of which may require substantial disassembly and/or removal of major engine components to diagnose and repair.

What are the common causes of code P2279?

Some possible causes of code P2279 could include the following, but note that this list is not complete, nor exhaustive, and that professional assistance and/or special equipment may be required to find and repair some vacuum leaks-

  • Leaking intake manifold gasket(s)
  • Defective MAF, MAP, or other implicated sensor
  • Leaking throttle body gasket/seal
  • Leaking fuel injector seals
  • Leaking brake booster vacuum line
  • Leaking or damaged brake booster diaphragm
  • Defective vacuum check valves and/or actuators in the boost control, and/or intake manifold runner flaps control system(s)
  • Defective PCV (Positive Crankcase Ventilation) system
  • Split, dislodged, damaged, or perforated vacuum lines/hoses anywhere in the engine vacuum system, or in the EVAP system between the EVAP purge valve and the intake manifold
  • Damaged oil filer cap seal
  • Failed or failing PCM, but note that since this is a rare event, the fault must be sought elsewhere before any control module is replaced

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