Twice within 72 hours my Citroen C5 automatic diesel saloon (reg May 2009) has ground to a halt within less than a mile of setting off. On both occasions the audible alarm and visual display came on to indicate a loss of oil pressure, followed by a gearbox fault. The engine automatically cut out within a few yards. First time round I called on the services of a national break-down company and he was there inside 30 minutes. A full visual/hands on examination followed by computer diagnosis revealed no faults. Second time I was able to restart the car within 20 minutes and get home without any problems. Any thoughts please?