Mass Air Flow Sensor (MAF)

Mass Airflow Sensor (MAF)
Mass Airflow Sensor (MAF)

When the air flow sensor signal vary significantly from expected range, the engine computer detects a fault and stores the corresponding fault code, illuminating "check engine" light on the dash. This fault or trouble code can be retrieved with a scan tool. Following trouble codes are usually associated with a mass air flow sensor:
P0100 - Mass Air Flow Circuit Malfunction
P0101 - Mass Air Flow Circuit Range/Performance
P0102 - Mass Air Flow Circuit Low
P0103 - "Mass Air Flow Circuit High"
P0104 - "Mass Air Flow Circuit Intermittent"
Trouble codes P0171 System Too Lean (Bank 1) and P0174 System Too Lean (Bank 2) are also often caused by a bad or contaminated mass air flow sensor. Read more about OBDII trouble codes.

How to test the mass air flow sensor

In some older cars an air flow sensor can be tested with a voltmeter. This procedure involves measuring signal voltage at different engine speed and comparing it to specificaed range. In most newer cars, however, an air flow sensor produces a digital signal and the only way to check it properly is to test it with a scan tool. If you have a good scan tool that shows live data, you can check mass air flow readings at different rpms and compare them to the specifications for your car or to the measurements from a known good MAF sensor at same rpms. Typically, a contaminated air flow sensor will show lower air flow than a known good sensor.
Sometimes poor electrical connection at the air flow sensor connector could also cause the air flow readings to be out of range. For this reason, the air flow sensor connector terminals as well as the wiring needs to be carefully inspected.

Air flow sensor replacement

If the air flow sensor is bad, it will need to be replaced. It's a fairly simple job, however the air flow sensor itself could cost up to $300-$400. If the sensor is just dirty, your mechanic may suggest to clean it (cleaning the air flow sensor is a delicate procedure) as a temporary solution; sometimes it could help. If the new mass air flow sensor is installed, make sure the air filter is installed properly, as the sand particles coming with the unfiltered air can damage the air flow sensor.
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