The mass air flow (MAF) sensor reads the air flow entering the engine. A defective MAF sensor can cause engine stalling, a rough running engine, and a check engine light for trouble codes like code P0171. Find out how to test a MAF sensor and how to replace a defective one with these tips from our mechanics.

Symptoms of a Bad or Faulty MAF Sensor

Rough running engine
Stalling engine
Check engine light for MAF code

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Steps to Take Before Testing the MAF Sensor

Look Under the Hood for Obvious Causes

If the engine is running rough or stalling out, check underneath the hood for obvious, loosely disconnected parts that may be the cause. Check for disconnected wires, hoses, and air intake tubes.

Check the Oil Condition and Level

Engine oil at full level and in good condition

Steps for Checking the Oil Level and Condition

Remove the oil dipstick
Clean off the dipstick
Reinsert and remove the dipstick
Confirm oil is between the two hashmarks
Check the condition of the oil—it should look clean

Inspect the Air Intake and Engine Air Filter for Damage

Inspect the sensor’s electrical connector’s terminals for discoloring or damage. Remove the air filter housing cover and check the condition of the engine air filter. Make sure it is clean, and clean the air box if needed since that can also affect the air flow.

Physically Inspect the MAF Sensor for Debris

Common part of the sensor to find debris that can affect readings — Common to find debris on wire of MAF sensor that can affect readings

Remove and check the MAF sensor for debris like dirt or leaves. These are sometimes found on the wire in the MAF sensor.

Consider Cleaning the MAF Sensor

Try cleaning the sensor with MAF sensor cleaner. Follow the directions listed for the particular cleaner.

How to Test a MAF Sensor with an Advanced Scanner

Stream a MAF Sensor Reading

You can get a reading of the MAF sensor with an advanced scan tool.

Connect to the vehicle’s computer and stream the MAF grams per second (GPS) reading. The reading should be fairly consistent and not drastically fluctuate, and should read higher at higher RPMs. Normal GPS ranges will vary depending on the engine size. Larger engines will have higher readings.

Test the MAF Sensor Reading

Wiggling a MAF sensor electrical connector

Wiggle the electrical connector and the wires and see if that causes a spike, which indicates the MAF sensor is faulty.

Replace the MAF Sensor and Watch the Reading

Replace the MAF sensor if it is faulty. Take another reading, and check if the sensor is working correctly and if replacing the MAF sensor improved engine performance.

Replace the MAF Sensor Yourself

Check out 1A Auto’s how-to videos and learn how to replace a faulty or dirty MAF sensor yourself with repair videos for many makes and models.

Common Steps for Replacing a MAF Sensor

Disconnect the Electrical Connector
Press the tab and disconnect the connector from the MAF sensor
Remove the Screws
Loosen and remove the screws from the MAF sensor
Remove the MAF Sensor
Remove the MAF Sensor
Install the New MAF Sensor
Insert the MAF sensor into place
Tighten the MAF Sensor
Tighten the screws to the new MAF sensor
Connect the Electrical Connector
Connect the electrical connector to the MAF sensor

How to Test a MAF Sensor