Fors Focus 1.8 Diesel 2006
I am getting a warning message of an engine system fault. No other warning lights coming on. Switch engine off and restart and message has disappeared. However, a few miles later (anything from 5 to 30 miles) and the warning message comes back.
No obvious loss of performance, although when the engine is under pressure e.g going uphille or accelerating hard, there is a lot of black smoke from the exhaust.
Any suggestions as to possible cause before I take it in to the Ford dealer? The simple dashboard diagnostic check shows no fault code.