How to know if the air flow sensor is out

Updated February 21, 2017

The mass airflow (MAF) sensor measures the amount of air entering a vehicle's engine through the fuel injection system. The MAF sensor is essential for controlling the flow of air and helps ensure a proper mix of air and fuel. When a mass air flow sensor is not functioning properly, your engine's efficiency will decrease and the emission control system will not operate properly. There are several signs that help you to determine when a mass air flow sensor is out.

Look at the instrument panel to see if the "Check Engine" or "Service Engine Soon" light is displayed. When a mass air flow sensor is malfunctioning, the engine computer detects a problem in one of the emission control system components and activates this warning light.

Start the engine and check for smoke coming out of the tailpipe. A bad MAF sensor affects the emission control system and will cause your car to run rich and expel smoke through the tailpipe. However, a defective MAF sensor also can cause the engine to run lean. You can determine if this is the problem by checking the tachometer to see if the rpm level is fluctuating when the engine is idling. Open the bonnet and check the spark plugs. If it is running lean, the spark plugs will be coated with white residue. On the other hand, if it is running rich, the spark plugs will be coated with black or grey residue.

Determine if the engine is running roughly, which can be a symptom of a defective mass air flow sensor. For instance, a bad MAF sensor will cause the engine to stumble and then recover when you start your car. It can also cause the engine to stall completely, requiring you to restart it. Other signs of a bad MAF sensor include delayed acceleration and the engine idling roughly while sitting at a traffic light.


If you have any of these symptoms, take your car to a professional who can run a diagnostic scan to determine if the MAF sensor is out. Some mechanics charge for this service and some do not, so it is a good idea to shop around.

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About the Author

Based in Orange County, Calif., Herman Cruz has been writing since 2007. His articles have been published in various content platforms and he also has written for Internet entrepreneurs who need assistance with writing sales letters and articles for their businesses. Cruz is pursuing his Bachelor of Arts in integrated composition, improvisation and technology at the University of California in Irvine.