Air Flow Restriction / Air Leak Between Air Filter and MAF


This code indicates that the PCM has detected a voltage reading from the mass air flow sensor and/or manifold air pressure sensor that points to an intake air leak on the unmetered side of the intake manifold.

Code Set Parameters

When the manifold air pressure sensor inputs a signal to the PCM that reflects a greater degree of intake air pressure than the mass airflow meter signal would suggest, a code will be stored and a malfunction indicator lamp may be illuminated. Some models will require multiple failure cycles in order for a malfunction indicator lamp to be illuminated.


Symptoms may include surging, unstable or fluctuating idle speed, lack of power, dead spots and hesitation upon acceleration, additional codes (especially engine misfire codes), spark knock, glowing exhaust manifolds and other components, and/or a hissing noise due to a vacuum leak. A stored code and service engine soon lamp illumination.

Common Causes

Common causes of this code are a disconnected or corroded electrical connector at the mass airflow sensor, moisture or debris that has contaminated the vane of the mass airflow sensor hot wire, a faulty mass airflow sensor, a torn or cracked air inlet between the mass airflow sensor and the throttle body, or a faulty PCM. PCM failures are rare. Almost any vacuum leak associated with the intake manifold may cause this code to be stored. These may include but are not limited to: the intake manifold gasket, various vacuum hoses and lines, throttle body gasket, a defective brake booster, a bad PCV valve, or a faulty injector o-ring.

Common Misdiagnosis

Often expensive mass airflow sensors are replaced when a simple cleaning of the mass airflow sensor “hot wire” could rectify the condition. Failure to thoroughly diagnose engine intake vacuum leaks may also lead to an incorrect diagnosis.


  • Most OBD-II systems utilize a mass airflow sensor, a manifold air pressure sensor, an intake air temperature sensor, and the oxygen sensors to calculate fuel strategy and the air/fuel mixture
  • The mass airflow sensor meters the amount of air entering the engine using a hot wire
  • The hot wire is energized using voltage from the PCM
  • As the amount of air passing over the hot wire and entering the intake manifold increases, the temperature of the hot wire decreases
  • The PCM interprets these variations in voltage as fluctuations in the amount of air entering the engine, then calculates fuel delivery and mixture strategy using this information along with input data from the manifold air pressure sensor, intake air temperature sensor, and the oxygen sensors
  • One of the least desirable conditions for an OBD-II controlled fuel injected engine is that of unmetered air entering the engine
  • Several tools will be instrumental in successfully diagnosing this code
  • A suitable OBD-II scanner (or code reader) and a digital volt/ohmmeter will be most helpful in performing a successful diagnosis
  • A manufacturer’s service manual (or the equivalent) will also be necessary
  • Begin with a visual inspection of all wiring and connectors
  • Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary
  • Always retest the system after repairs are completed to ensure success. If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data
  • This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored
  • Continue by clearing the code and operating the vehicle to see if it returns
  • This will help to determine whether or not the malfunction is intermittent
  • After the codes are cleared, test drive the vehicle to see if the code returns
  • If the code fails to immediately return, you may have an intermittent condition
  • Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can be made. Determine whether there is a malfunction in system circuitry or a problem with unmetered air entering the engine by listening for an intake vacuum leak
  • A stethoscope or other listening device can be helpful when diagnosing this type of code
  • Start the engine with the vehicle in neutral or park and use the listening device to detect any abnormal hissing noises that may be caused by a vacuum leak
  • Pay particular attention to areas such as the intake manifold and throttle body gaskets, the EGR valve, air inlet tubes, vacuum lines and hoses, the brake booster (especially when the brakes are applied), and fuel injector seals
  • If any abnormal hissing is detected, use a spray aerosol carb and fuel injection cleaner or propane torch to pinpoint the leak
  • Use caution when using flammable compounds in the engine area
  • Once a vacuum leak has bee pinpointed, repair the condition as required and clear the codes
  • Test drive the vehicle to ensure that the repair has been completed successfully. If no engine vacuum leaks are detected visually inspect the vane or hot wire of the mass airflow sensor itself for signs of signs of dirt or other debris
  • This can be removed by carefully using an approved chemical agent and a cotton swab, then blowing dry with compressed air
  • After the repair is completed, clear the codes and test drive the vehicle to make sure it has been successfully completed. If the hot wire of the mass airflow sensor appears clean, follow the manufacturer’s recommendations for testing the mass airflow, manifold air pressure, and manifold air temperature sensors and system circuitry
  • Repair or replace system circuitry and/or components as required and clear the codes
  • Test drive the vehicle after repair are performed to ensure that they are successful.