The task of the poor-road-surface detection is to diagnose that the vehicle is driving over a poor road surface (stones, rubble, etc.) on the basis of the wheel acceleration supplied.
As soon as a poor road surface is detected, a fault is entered and the misfire recognition is disabled temporarily. This disabling is necessary because drive train vibrations caused by poor road surfaces can lead to incorrect detection of misfires.
On the other hand, it is possible that the poor-road-surface detection takes effect too late, i.e. only after misfires have been erroneously detected. In this case, the misfiring fault codes can be recognized as incorrect diagnoses by the poor-road-surface detection.