WHILE I WAS DRIVING ON THE HIGHWAY, APPROXIMATELY 55MPH; THE CHECK ENGINE LIGHT CAME ON; SMELLED LIKE PLASTIC BURNING AT THE SAME TIME; I WAS ABLE TO STOP ON EXIT RAMP AS THICK BLACK SMOKE FILLED THE INSIDE. GOOD SAMARITANS HELPED ME GET OUT AS FLAMES WERE IGNITED UNDER THE HOOD. SEVERAL LIKE MINI EXPLOSIONS ACCOMPANIED THE FLAMES.