Engine system fault

7th December, cold frosty start and the engine started normally, there was a sound like a warning buzzer from behind me and the lcd display came up with "engine system fault" and the red light came on alongside it. All other lights were off and the car ran normally. After a few seconds the buzzer stopped and has not reoccurred. When the engine is switched off and then back on the warning display comes on after a few seconds and remains on but the ngine runs normally, I have tried a short jouney with absolutely no problem with the car though the display is on all the time. Any ideas?