M47D20TU2

Warning light, limp mode, oil level rising above the maximum mark from fuel dilution. The filter needs sustained hot running to regenerate. A car used for short urban trips never completes a regeneration cycle.

Check: Read the DPF soot load and the distance since the last regeneration on a scan tool, and check the engine oil level and smell it for diesel. Ask what the car was used for. A short-trip city diesel is the wrong car regardless of mileage.

Sudden loss of power on a hard pull, limp mode that clears on restart, underboost or overboost codes. Soot binds the variable vanes or the actuator linkage seizes.

Check: Do a full-throttle pull in third from 1,500 rpm to the limiter. Hesitation or a drop into limp mode is this fault. Do this twice.

Often none until it happens. Rough running, then in the worst case an engine destroyed by an ingested flap. The intake manifold's swirl flaps run on spindles that wear. A detached flap can be drawn into a cylinder.

Check: Not visible without removing the manifold. Ask whether the flaps have been removed or the manifold replaced. Many well-kept examples have had this done preventively, and that's a selling point.