A mass air flow sensor is a component in your vehicle's engine bay (under the hood) that is used to calculate the mass of air entering the fuel injection system, and ultimately, the engine. The mass of air entering the engine is critical for proper air/fuel mix. The information gathered by the mass air flow sensor or "MAF sensor" is captured at the air intake and sent to the engine control unit (ECU) to balance and deliver the correct fuel mass to the engine. Before you replace a mass air flow sensor (they're expensive), there is a test you can perform to tell if a mass air flow sensor is bad.
Inspect the MAF sensor for any dirt, dust, or other debris. Make sure that the sensor is free of any contaminants.
Set your voltmeter to the Ohms setting and measure the resistance between terminals THA and E2. To do this, place one lead on the voltmeter on the THA terminal, and another lead on the E2 terminal. The reading should be at or near 0. If it is, move on to step 3. If it is not, your air flow meter is faulty.
Turn the ignition switch to the "on" position in your vehicle.
Set the voltmeter to "volts" and connect the positive lead to the VG terminal and the negative lead to the E2G terminal.
Blow into the air intake air flow meter and check to make sure that the voltage fluctuates. If it does, your mass air flow sensor is working properly. If the voltage does not fluctuate, then your air flow meter is faulty.