Mass Air flow Sensor Functions and Failure Symptoms

November 13, 2016 | Electrical Repair Info


Basic Functions of  Mass Air flow Sensor

As the name suggests a mass air flow sensor measures the flow of air into the engine, known as the engine load, so that appropriate fuel mass can be provided to the engine. Apart from this it also adjusts for the density of the air. A lot of Vehicles make use of this sensor in their engine control system nowadays.

Variable voltage output and frequency output are two common designs of MAF used recently. The operation of both designs is the same and the output can be measured by a scanner or an ohm meter.

The function of mass air flow sensor can be understood by the hot wire principle in which a constant voltage is given to a heated wire. This wire is placed in the air channel and heated so that it produces voltage. As air flow through the channel, the wire cools down. The wire is a heated PTC resistor; this implies its resistance downslides as its temperature falls. This drop causes more current to flow through it so that the desired temperature is maintained. This current is transformed into frequency or voltage and is sent to the computer which decodes it as air flow. Air temperature and humidity are two constraints that also need attention as they affect the temperature of the heated wire as well.

Read also: Crankshaft position sensor symptoms

Symptoms of a Bad Mass Air flow Sensor

A bad sensor displays a temperature of the air more than the coolant level; this causes the engine control unit to reduce the fuel flow, followed by lean operation and reduction of the fuel economy. On the other hand if the temperature is very low, too much fuel is given in, resulting in high operating condition, which also is not fuel economical.  The major symptom through which you can diagnose whether the MAF is poorly functioning is when the engine performance is hindered. This means that your engine is hard to start, stalls quickly after starting, and skids while under load, jerks when accelerated, hiccups or displays rich idling. You should also look for the check engine light on the instrument; its illumination is what you can rely on while concluding about a bad MAF. Other symptoms include low vacuum, low compression, and low fuel pressure resulting from a bad fuel pump.

And then of course, you always have the option of taking your car to an auto mechanic and getting it checked for a fee. You can also do computer scanning yourself by plugging a digital auto diagnostic scanner into the car’s OBD 2 diagnostic port.

After inspecting carefully and concluding that it’s your MAF that’s causing your car to behave abnormally, you will need to get your MAF replaced. Though some experts might advise you on replacing but it’s usually more cost effective to get a new one rather than repairing it.


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