Error "depollution system faulty" shown in multi-display and check engine light lit.
Check engine light lit, but the engine was running normal.
I read the ECUs Diagnostic Trouble Codes (DTC) and got error code P0170 (Fuel supply correction).
I filled the petrol tank full and added a bottle of Fuel Injector Cleaner.
I then took the car for a "blast", 30 min. running at 110-120 km./h. (approx 70 miles/hour).
Afterwards I deleted the error code.
The error code has not reappeared.