DTC codeP0104 OBD2 is stored when the Mass Air Flow (MAF) sensor circuit is malfunctioning. This sensor is used to measure the density and volume of air entering the engine. It is worth mentioning that this sensor only measures a part of the air and this value is used to calculate the density and the total volume that is ingested.
The PCM (Powertrain Control Module) receives this information from the MAF sensor, and other parameters, to ensure proper fuel delivery at a given time. In this way, the optimum power is achieved and the engine fuel is more efficient.