Calculated engine load (PID $04) is determined (according to SAE J1979) by equation:

LOAD_PCT = [current airflow] / [(peak airflow at WOT@STP as a function of rpm) * (BARO/29.92) * SQRT(298/(AAT+273))]

⎯ STP = Standard Temperature and Pressure = 25 °C, 29.92 in Hg BARO,

⎯ SQRT = square root;

⎯ WOT = wide open throttle, AAT = Ambient Air Temperature and is in °C

Does "peak airflow" parameter is possible to read from ECU or does it know only by manufacturer to provide PID $04? Generally can I calculate this value manually with using of available parameters from ECU?