Case happened at the Help Desk.

The car arrived at the workshop with a performance problem and engine light on, mileage about 160,000 km.

Diagnosis with Smart tester detects error P1206: DPF air resistance monitoring. Particulate filter.

At first analysis suggested forced regeneration and given the mileage to clean the intake duct and EGR anyway.
DPF regeneration is successful but after a few kilometres the fault recurs.

Solved by replacing the DPF filter.