What is a mass air flow sensor and where is it located?

The majority of vehicles on the road today are equipped with a mass air flow sensor (MAF), also commonly referred to as an air flow meter. The mass air flow sensor is a device that measures the amount of air entering the engine and supplies this information to the engine control unit (ECU). The ECU uses this information to calculate engine load, which the ECU uses along with information provided by the oxygen sensor(s) to precisely control the engine’s air / fuel ratio. Engine load measurement is also needed to control other functions such as automatic transmission shift points on many vehicles. 

Your vehicle’s air flow meter is located between the air filter and throttle body along the air intake stream. The appearance of the MAF sensor will differ depending on what kind of sensor your vehicle uses, as there are a few different types of mass air flow sensors commonly used on cars and trucks.

Hot Wire Mass Air Flow Sensors

One of the more common mass air flow sensors used today is the hot wire sensor. This type of MAF sensor measures air mass directly. It uses an electronic control unit, a temperature sensor, and an electronically heated wire(s). This wire is heated and maintained at a certain temperature. As engine load increases, air passes through the sensor cooling the wire. In turn, more voltage is needed to bring the wire back to temperature. This voltage is directly related to the mass of the air entering the engine.

Cold Wire Mass Air Flow Sensors

Many General Motors vehicles use a cold wire MAF sensor. This sensor works just like a hot wire sensor, however it uses a “cold wire” that supplies the ECU with the ambient air temperature. This information is useful because different air temperatures will cool the hot wire at different rates.

Karman Vortex Mass Air Flow Sensors

Karman vortex air flow meters do not directly measure mass air flow. These meters measure air temperature, pressure, and volume. The ECU uses these three measurements to calculate the mass air flow. This type of meter uses a metal foil mirror, a vortex generator, and a photo receptor. The vortex generator disrupts the air, creating what is known as a Karman vortex. The frequency of these vortices or “swirls” is directly related to the speed of the air. These sensors also incorporate an internal temperature sensor and barometric pressure sensor.

Vane Air Flow Meters

A vane air flow meter (also known as a “flap style” meter and a VAF sensor) is an early type of air flow meter that measures air intake volume. This type of meter uses a spring-loaded flap that is attached to a variable resistor. As air enters, it pushes against the flap or plate opening it. The movement of the flap opening is converted to voltage, and the signal is sent to the ECU. VAF sensors also contain an intake air temperature sensor.

How do I know my mass air flow sensor / meter needs to be replaced?

Regardless of the type of MAF, they are all vulnerable to dirt or debris. If contaminated, these sensors are unable to provide the ECU with accurate information. Keeping up with scheduled maintenance, inspecting and replacing a dirty or clogged air filter is crucial.

Symptoms of a bad air flow sensor may include:

• Rough Idle
• Power Loss
• Reduced Gas Mileage
• Hard Starting
• Stalling at slow speeds

Hot and cold wire MAF sensors are particularly prone to dirt and oil contamination, as well as moisture. Although it is possible to clean a mass air flow sensor, using a cleaner specifically made for MAFs, it is important to remember the components are particularly fragile and can be easily damaged. It is widely recommended to replace a faulty MAF sensor rather than clean it. 

Common symptoms related to a failed or faulty mass air flow meter include an erratic idle, stalling, or inability to hold idle, loss of power, reduced gas mileage, bad throttle response, or even a no-start condition. When diagnosing a faulty mass air flow sensor, it is important to check for oil or dirt contamination, intake leaks after the sensor (such as cracked / broken vacuum lines, air intake hose, throttle body or intake manifold leaks), and broken or frayed wiring. All mass air flow sensors and meters can be tested on or off the vehicle by a variety of methods, although methods differ depending on application. Common OBDII Trouble Codes related to mass air flow sensors / meters include:

P0100 - Mass Air Flow Circuit Malfunction
P0101 - Mass Air Flow Circuit Range/ Performance Problem
P0102 - Mass Air Flow Circuit Low Input
P0103 - Mass Air Flow Circuit High
P0104 - Mass Air Flow Circuit Intermittent
P0170 - Fuel Trim Malfunction (Bank 1)
P0171 - System Too Lean (Bank 1)
P0172 - System Too Rich (Bank 1)
P0173 - Fuel Trim Malfunction (Bank 2)
P0174 - System Too Lean (Bank 2)
P0175 - System Too Rich (Bank 2)

Can I replace the mass air flow sensor myself?

Replacing the MAF sensor can be fairly simple provided you have basic knowledge of automobiles and the right set of tools. The repair will usually require the steps of locating the sensor, which can usually be found inside the air duct between the air filter and the engine, and then disconnecting the negative battery cable. Depending on the vehicle, you may have to remove part of the air intake to access the sensor. Once you've reached the sensor, disconnect the wiring harness and remove the vacuum hose. Then remove the screws/bolts holding the sensor in place and remove the old sensor. The install the new one, simply reverse the procedure.

If you replaced the sensor and the engine light is still on, there are a few things you can do. The engine rarely shuts off of the check engine light after replacing the mass air flow sensor. If your check engine light is still on but the engine is running fine, the light will probably go off after a few cycles of driving with the new sensor (on some vehicles this could take as many as 50 cycles of turning the key on and off). You can also have the code cleared with the correct scan tool. Another possible remedy is to disconnect and reconnect the battery, although this may not work on all vehicles.

Need a mass air flow sensor replacement?

If your engine is not running properly because of a defective air flow meter, 1A Auto has your answer. We are your source for mass air flow sensor replacements! We have quality aftermarket mass air flow sensors for many makes and models, and all at great prices.

1A Auto MAF Sensor Features:

• Strict quality control specifications ensuring you receive a durable sensor
• Compare a 1A Auto air flow sensor to an OEM sensor and save 30-50%
• Direct replacement mass air flow sensor for convenient installation