1.15.6.4 Rationality check

P115C (HFMRsig), P115D (HFMRnpl) 

Depending on engine speed and throttle position, a theoretically expected maximum and minimum mass airflow is calculated at these engine conditions and compared to the actual measured mass airflow.

If the measured mass airflow from the MAF sensor lies below the theoretically expected minimum mass airflow for a calibrated period of time, a malfunction is detected and a HFMRsig fault will be set.

If the measured mass airflow from the MAF sensor exceeds the theoretically expected maximum mass airflow for a calibrated period of time, a malfunction is detected and a HFMRnpl fault will be set.