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7 Symptoms of a Bad Mass Air Flow Sensor

An arrow points to the mass air flow sensor in the engine bay

Modern electronic engine controls calculate the correct quantity of fuel for a given situation. Several sensors and actuators come into play, such as the mass air fuel (MAF) sensor and fuel injectors, and just as with any other car part, these sensors and actuators can degrade over time. If your vehicle is having performance issues, you may be experiencing one of the symptoms of a bad mass air flow sensor.

What Is a Mass Air Flow Sensor?Mass air flow sensor

The mass air flow sensor measures the air mass flowing into the engine intake. Measuring air mass is critical in calculating how much fuel to add to achieve the correct air-fuel ratio (AFR). The ideal AFR is 14.7:1 (14.7 pounds of air to 1.0 pounds of gasoline), but real-world AFR varies. Acceleration might require a rich AFR, up to 12:1, while cruising requires a leaner AFR, sometimes as low as 22:1. If you have a bad MAF sensor, the engine control module (ECM) cannot calculate fuel injection correctly, which can lead to larger issues with your vehicle.

7 Symptoms of a Bad Mass Air Flow Sensor

There are several symptoms of a bad MAF sensor, and not all of them are immediately obvious:

  • Illuminated Check Engine Light: Performance and circuit diagnostic trouble codes may refer directly to the MAF sensor, but fuel trim and misfire codes can also be linked to the MAF sensor.
  • Trouble Accelerating: If you’re having problems accelerating into highway traffic or while passing, the ECM may be limiting injection due to MAF sensor problems.
  • Rough Idle: Smooth idle is difficult to achieve without the proper amount of fuel. If the MAF sensor has issues, the engine may not run smoothly, especially while idling.
  • Poor Fuel Economy: The MAF sensor does not have to fail completely to affect fuel economy. If the ECM errs rich, it may add more fuel than necessary, causing poor fuel economy.
  • Black Exhaust Smoke: In some cases, the ECM may err so rich that black smoke comes out of the exhaust. This can also overload the catalytic converter.
  • Hesitation or Surging: During acceleration or cruising, you might notice hesitation or sudden abnormal power, which can be unnerving.
  • Hard Starting: Engine starting requires more fuel than idling, but the ECM may not command enough fuel injection to start the engine right away if the MAF sensor signal is skewed.

These issues don’t always mean that your MAF sensor is faulty. A vacuum leak, a clogged air filter, restricted exhaust, a clogged catalytic converter or a broken intake tube can mimic a bad MAF sensor, so check the intake system to rule those issues out first.

How to Fix a Bad Mass Air Flow Sensor

If your intake system is good to go and you’re still having issues, there are several things you can try:

  • Shake out the dust. Blow out the intake tubing and install a new air filter to prevent future dust intrusion.
  • Use a cleaner. An MAF-sensor-specific cleaner may be able to take care of any contamination.
  • Replace it. If neither of these steps is effective, replacing a mass air flow sensor is usually a simple job.

Diagnosing drivability issues is a process of elimination. Compare your vehicle’s components with known-good signals for accurate diagnosis and quick repair.

Check out all the sensors available on NAPAonline or trust one of our 17,000 NAPA Auto Care locations for routine maintenance and repairs. For more information on mass air flow sensors, chat with a knowledgeable expert at your local NAPA Auto Parts store.

Photo courtesy of Wikimedia Commons.

Benjamin Jerew View All

Ben has been taking things apart since he was 5, and putting them back together again since he was 8. After dabbling in DIY repairs at home and on the farm, he found his calling in the CGCC Automobile Repair program. After he held his ASE CMAT for 10 years, Ben decided he needed a change. Now, he writes on automotive topics across the web and around the world, including new automotive technology, transportation legislation, emissions, fuel economy and auto repair.

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