Signs & symptoms of a defective mass air flow sensor

Written by karie lapham fay
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Every car has a mass airflow sensor (MAF). A critical component for engine performance and power, the MAF measures the flow and density of air into the combustion chamber of the engine. The resulting voltage tells the vehicle computer to adjust the injector pulse to change the amount of fuel delivered. If the MAF fails, the vehicle will not run correctly.

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Check Engine Light

The most obvious symptom of MAF failure is a "check engine light" lit on the vehicle dashboard. When an engine sensor fails, the vehicle computer reverts to code values stored in memory to compensate for the loss of a signal from the sensor involved. At the same time, a fault code is transmitted, triggering the check engine light to come on. The vehicle computer registers the fault code in its memory. Hook up the vehicle computer to a code reader to determine the fault code, which diagnoses the sensor involved and possible causes.

Power and Performance

Remember that the MAF determines the mixture of air and fuel required for engine performance. So, MAF failure will create a wide variety of performance and power problems. These may include: hard to start vehicle; starts and immediately stalls; hesitation in engine; rough idle; running very rich or very lean fuel mixture; or "hiccup" when accelerating.

These symptoms can appear before the MAF fails to the degree that the check engine light appears. And other vehicle engine problems can also cause these symptoms, so proper diagnoses must be performed and the engine light cannot be relied on.


As All Ford Mustangs explains, a very common cause of MAF failure is dirt passing through the air filter. Cleaning the MAF can be a very simple, inexpensive fix to attempt.

The MAF is mounted on the air cleaner. It connects to the vehicle computer with a wiring harness. Unbolt the MAF and disconnect the wiring to remove the MAF housing. Next, gently remove the screws on top and gently pull the MAF sensor out. If the two filaments revealed inside the MAF are dirty or dark in colour, clean carefully with a cotton swab. An electrical contact cleaner also works very well. After cleaning, allow to air dry before reassembling. Also visually inspect the wiring harness for loose or dirty connectors or bad wires.


If you suspect MAF sensor failure and the check engine light is on, a parts store can read the computer code with a code scanner or even sell you a code scanner. An auto repair shop can also check the codes fairly easily. But if the check engine light is not on and you suspect MAF failure, try the cleaning first.

After cleaning, if engine performance increases or the check engine light goes off, then a dirty MAF was likely the problem. If, however, it does not eliminate the problem, a mechanic can perform more in-depth tests. If the MAF is indeed broken, then it is much easier and cheaper to simply replace the sensor then repair it, and a competent do-it-yourselfer can change it quickly.

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