Having knowledge of certain trouble codes may be beneficial. However, it is important to determine the specific engine model of your M5, such as the Pug 1.6 DV6 or the Mazda 2.2, before proceeding. Secondly, if the issue were just related to oil degradation, it would merely result in a flashing DPF light. However, as previously said, providing specific fault codes would assist in identifying and resolving the problem at hand.