Mass Air Flow Sensor
A MAF (Mass Air Flow) sensor measures the mass of air passing through the air tube. It is calculated by multiplying air density by air volume. There are several types found on vehicles today. These include the cold wire, heated wire, Karmen Vortex, and vane type MAF sensors. The vane sensor is also known as an airflow meter.
A vane type MAF sensor uses a paddle or door that moves as the air rushes by. This type of sensor utilizes a potentiometer (variable resistor) to send a variable or changing voltage signal to the PCM in proportion to air volume.
A cold wire MAF sensor uses thin metal strips that vibrate as the air passes by. This vibration changes in frequency as does the signal sent to the ECM.
A hot wire MAF sensor has a heated filament like a toaster. The sensor's resistance changes or decreases as cool air passes by the filament. The increase in current to maintain the sensor's heat is converted to a voltage signal and sent to the PCM to adjust the air-fuel ratio.
Because this heated filament gets dirty from time and wear, a cleaning may return the MAF to its normal operating condition. There are many products designed to clean a dirty MAF sensor on the market, and the whole process usually only takes a few minutes. Just remove the sensor and spray the filament until it is clean, then re-install the sensor.
Symptoms of a dirty MAF sensor include loss of power, hesitation and stumble, and reduced gas mileage. At low speeds, a dirty MAF signals the PCM to add fuel, resulting in excessive positive (LTFT) Long Term Fuel Trim. Excessive positive LTFT (+ 10%) typically indicates a persistent lean fuel condition. The PCM will illuminate the check engine light when the fuel trim exceeds 25% in either direction.
The Karmen Vortex air flow meter does the same thing but creates a vortex that is sensed by a photocoupler and a mirror. This signal is converted to a voltage signal to be sent to and interpreted by the PCM.
The MAF sensor provides the ECM and TCM with valuable information regarding engine load. The transmission control unit uses this information for shift control. A mass air flow sensor left unplugged, faulty, or in need of cleaning will affect a vehicle's shift control dramatically.