The Mass Air Flow (MAF) sensor uses a hot wire sensing element to measure the amount of air entering the engine. Air passing over the hot wire causes it to cool. This hot wire is maintained at 200°C (392°F) above ambient temperature as measured by a constant cold wire (Figure 36). If the hot wire electronic sensing element must be replaced, then the entire assembly must be replaced. Replacing only the element may change the air flow calibration.
The current required to maintain the temperature of the hot wire is proportional to the air mass flow. The MAF sensor then outputs an analog voltage signal to the PCM proportional to the intake air mass. The PCM calculates the required fuel injector pulse width in order to provide the desired air/fuel ratio (Figure 37). This input is also used in determining transmission Electronic Pressure Control (EPC) , shift and torque converter clutch scheduling.
Some MAF sensors have Integrated Bypass Technology (IBT) with an integrated Intake Air Temperature (IAT) sensor. The present applications with IBT are: Focus, Escort (4V), 2.0L Cougar, Escape, Taurus/Sable, Windstar, Explorer/Mountaineer and E-Series.
The MAF sensor is located between the air cleaner and the throttle body or inside the air cleaner assembly.