Mass Air Flow (MAF) Sensor
The MAF sensor provides an analog voltage signal to the PCM proportional to the intake air mass. The MAF sensor uses a hot wire sensing element to measure the amount of air entering the engine. The hot wire is maintained at 200°C (392°F) above the ambient temperature. Air passing over the hot wire cools the wire. The current required to maintain the temperature of the hot wire is proportional to the air mass flow. The MAF signal is used to calculate the EGR flow rate and for concern detection.
The current PCM implementation contains a mass air flow interface, which consists of a 2-pole, differential input, low pass filter. This filter is designed to pass an analog signal, originating from the mass air sensor, while rejecting unwanted ignition noise, high frequency electrical interference, and ground offsets. The input to the interface is the analog voltage signal difference between MAF+ (mass air flow signal) and MAF- (mass air flow return). The MAF sensor output an analog voltage signal calibrated to 0.5 V at the lower limit of the flow range and 4.75 V at the upper limit of the flow range.