What is a mass air flow sensor and how to test a mass air flow sensor

What is a mass airflow sensor

A mass airflow sensor is used to detect the mass flow rate of air which enters an engine. The details which are collected by the airflow sensor are used by the engine control unit, in order to determine how much fuel to inject, when to ignite, and when to shift the transmission. The airflow sensor is located in the intake air system, between the air cleaner and the throttle body. The air mass details are needed for the engine control unit to balance and deliver the proper fuel mass to the engine, air will change its density when it expands and contracts with temperature and pressure. Most newer fuel injection system uses a mass airflow sensor to calculate the amount of air volume delivered to the engine.

How does a mass airflow sensor work

The primary component of the mass airflow sensor is a thermistor, platinum wire, and an electronic circuit. An intake air temperature sensor is present in the MAF sensor as a part of the housing assembly. The thermistor will measure the temperature of the incoming air. The hot wire is maintained at a constant temperature in relation to the thermistor by the electronic control circuit if the airflow increases then the hot wire will lose the heat faster and the electronics control circuitry will compensate by sending more current through the wire. The electronic control circuit measures the current flow simultaneously and then it will put a voltage signal proportional to the current flow.

What are the types of airflow sensor

There are two types of airflow sensors they are hot wire airflow sensor and the vane-meter.

Hotwire airflow sensor

This type of sensor can measure the air mass flow and the principle of this type of air mass flow meter is that when the air passes through the hot wire it will cool the hot wire. There is a circuit in order to increase the current through the wire as the air cools the wire so the current will be proportional to the airflow, and there is a resistor to compensate the temperature variations. The hot wire is made up of platinum and it is only a few millimeters long and because of its small size the time constant of the sensor is very short and this is a big advantage because any pulsation of the airflow can be detected and control unit will react to it accordingly

Vane airflow meter

In this type, the vane airflow meter provides the ECM with an accurate measure of the load placed on the engine. vane airflow meters have the following components measuring plate, compensation plate, return spring, potentiometer, bypass air passage, idle adjusting screw, fuel pump switch, intake air temperature sensor. This sensor will measure the airflow into the engine with a spring-loaded air flap attached to a variable resistor. The vane will move according to the airflow and the voltage will be proportional to the distance the vane moves so the vane movement controls the amount of fuel injected.

What happens when the MAF sensor goes bad

If the MAF sensor is bad in an engine, this engine could be hard to start or it may stall after starting. It could also hesitate under load, surge, and the engine may also hiccup when the throttle suddenly changes position.

How to test the MAF sensors or how to know if the mass airflow sensor is working

Testing of these sensors can begin by visual inspection, we must check all the hoses that direct and send air. Mostly the part between the MAF sensor and the throttle body and the electrical connectors must be checked for corrosion, frayed wiring, and for terminals which is bent or pushed out of the plastic connector.

The second stage is MAF’s sensor output test these sensors calculate the air mass by weight in a given amount of time, a digital multimeter can be used to check the DC volts on the signal wire circuit. Tap tests can be done to test the MAF sensors so while the engine runs at idle speed gently tap the MAF sensor if the engine stumbles or stalls then the MAF sensor is defective.

What are the contaminations in MAF sensor

Dirt, oil or silicon can coat the sensing wire because it tends to insulate the sensing wire at low airflow rates. Because of the contamination in the sensor, it could underestimate the amount of air entering the engine. Due to this, the fuel system will go lean causing spark knock and lack of power concerns. In order to check the contamination check the fuel trim numbers.