Symptoms of a Faulty or Faulty Mass Air Flow Sensor

Common signs of MAF sensor problems include rich idle or lean under load, poor fuel efficiency, and rough idle.

Mass air flow (MAF) sensors are responsible for transmitting the amount of air entering the engine to the powertrain control module (PCM). The PCM uses this input to calculate engine load.

There are several designs of mass air flow sensors, but the hot wire MAF sensor is the most common today. The hot wire mass air flow sensor has two sense wires. One wire gets hot and the other doesn't. The microprocessor (computer) inside the MAF determines the amount of air going into the engine by how much current it takes to keep the hot wire about 200℉ hotter than the cold wire. Whenever the temperature difference between the two sensing wires changes, the MAF will either increase or decrease the current to the heated wire. This corresponds to more air in the engine or less air in the engine.

There are a number of drivability issues that result from faulty MAF sensors.

1. Runs rich at idle or leans under load

These symptoms indicate that the MAF has a contaminated hot wire. Contamination can come in the form of cobwebs, sealant from the MAF sensor itself, dirt that sticks to the oil on the mass starter due to an over-lubricated secondary air filter, and more. Anything that acts as insulation on a hot wire will cause this kind of problem. Fixing this is as simple as cleaning the mass air flow sensor with an approved cleaner, which AvtoTachki technicians can do for you if they determine this is the underlying problem.

2. Constantly getting richer or thinner

A mass air flow sensor that continually raises or lowers airflow to the engine will cause the engine to run rich or lean. If the engine management system is working properly, you will probably never notice it, other than a change in fuel consumption. A trained technician will need to check the fuel trim status with a scan tool to verify this. A mass air flow sensor that behaves this way needs to be replaced. However, the rest of the circuit must be checked for proper operation before replacing the sensor. If there is a problem in the circuit, replacing the sensor will not solve your problem.

3. Rough idle or stalling

A completely failed MAF sensor will not send airflow information to the PCM. This prevents the PCM from accurately controlling fuel delivery, which will cause the engine to idle unevenly or not at all. Obviously, in this case, it is necessary to replace the mass air flow sensor.