You have to take it to a workshop, It is very likely that the particle filter is clogged with ollin and must be changed. This warning is that of the engine gases, if the ECU considers that the engine may suffer a gravel failure, it goes out. Some people put the car in 4th and about 2500 rpm for 40 km and the filter is cleaned. Other times the ollin is petrified and the obstruction is such that it must be replaced. Diesel cars with particulate filter with short gears break down at low speed. The usual thing is to zapate them on the road every so often.