Most 2021 5 Series diesels use a 48V mild‑hybrid system that assists start/stop and gives a small torque boost — it doesn't need plug‑in charging and the battery is much smaller than a PHEV, so few of the battery degradation issues of plug‑ins. As a diesel saloon this variant suits long runs best; check for diesel-specific items like DPF/EGR and AdBlue equipment, and that the automatic (ZF 8‑speed) shifts smoothly and has had any recommended software/fluid updates.

• DPF and EGR condition — signs of frequent forced regens, warning messages or heavy smoke (common if used mainly on short urban trips)
• AdBlue system operation and consumption — check for warning lights and any injector/consumption faults
• 48V mild‑hybrid battery/module operation — confirm start/stop works normally and look for hybrid system fault warnings
• Automatic gearbox behaviour and service history — smooth, consistent shifts with no hesitation or harsh kicks; ask about any gearbox fluid/软件 updates
• Turbo and oil-leak signs — watch for blue/black smoke under acceleration and check around turbocharger for seepage or oil leaks