Over the last few months I have experienced numerous irregular warnings for a fault in the lighting system; the warning shows on the central display for a few seconds and then stops. When I check the condition of all lights they are fine. On two occasions, when the outside temp was close to zero, the speedo/rev counter stopped working and the turn indicators would not operate - after 30 seconds or so it all went back to normal. I am now getting occasional warnings of low tyre pressure; tyres checked and pressures correct - this warning has to be reset via the iDrive controller. The main car battery was replaced recently and shows 12.6v using a multimeter. The alternator shows it charging at 14.9v at idle. A diagnostic check at an independent garage revealed no fault codes saved on the system. Any ideas?