The mass air flow sensor is designed to measure the amount of the air an engine takes in. As we all know, the prefect ration for oxygen and gas in the engine is 14.7:1, so it does some damage to your engine either the ratio is too high or too low. The mass air flow sensor read how much air coming into the engine and sends this information to computer, and the computer calculates the proper amount of the fuel needed for the highest engine performance. It is common for mass air flow sensor get dirty and get failing, so pay attention on your mass air flow sensor is any symptom happen as following: if the Check Engine Light is on; if your Subaru car doesn't have power; if there is an excessive fuel consumption; if your Subaru car fails at starting. Save your money by ordering a Subaru genuine OEM mass air flow sensor here with a discounted price and change it by yourself.