Mass Air Flow Sensor MAF

The mass air flow sensor (MAF) is used to monitor the amount of air going into the engine while running. Mass air flow sensors work in conjunction with the oxygen sensor and the engine control system to maximize performance and economy. A vehicles mass air flow sensor delivers a signal to the PCM computer (powertrain control module) telling the amount of air coming into the engine. This is compared with oxygen levels in the exhaust to determine the efficiency of the engine. It is usually difficult to detect when a mass air flow sensor fails, the "check engine light" or engine symbol will probably not be illuminated. Your car, truck or SUV may have a poor idle quality, stall, low power or all three. Your PCM may have no trouble codes because the PCM cannot detect a problem since the sensor is working but is out of range.

Mass Air Flow Sensor MAF
Mass Air Flow Sensor MAF

What has occurred with most mass air flow sensor failures is the sensing element or "hot wire" that is used to give electronic feedback to the PCM for processing has become contaminated by air particulates. The mass air flow sensor is reporting to the PCM that less air is running through the engine than actually is. The PCM will then lean the fuel mixture down to the point that it will cause performance issues. There is not enough variance in the system to trigger a MIL "service engine soon" light so this particular repair problem can be difficult to detect through normal troubleshooting methods.

A mass air flow sensor is most common in newer vehicles, this sensor is used to help maximize efficiency and reduce emissions. One of the benefits of the mass air flow sensor is that it can respond to changes in air intake flow. There are no moving parts in a mass air flow sensor. Most vehicles mass air flow sensor locations are in the air intake for the engine, this allows easy replacement. It is recommended that the sensor be replaced approximately every 60,000 miles.

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35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2013-11-21)