I have a 08 c5 1.6 diesel, ocassionally the car stalls with no warning. The power steering brakes fail. it is very dangerous. a sign "depollution system faulty comes up. The car will come to a stop. I turn off ignition, restart car . it starts immediatedly no problem and no warning sign on dash. Any ideas please. I am afraid of it happening on motorway especially on fast lane.