Rationality check

P152B 

To determine the rationality of the vehicle speed several checks are performed. The fuel cut-off check compares the vehicle speed during fuel cut-off condition. It is assumed that the vehicle must move during this condition. To cover the special fuel cut-off case when the driver has rev-up the engine at standstill the check must be debounced for a calibrated time.

If the vehicle is in fuel cut-off condition and the vehicle speed lies below a calibrated threshold for a calibrated (debouncing) time, a malfunction is detected and a minimum fault VFZNP is set.