not an expert but my thought is i belive the nominal output from the alternator should be 13.2 volts if this drops below for any reason it may trigger the fault if with the engin running the voltage reads 13.2-14.2 all should be fine try checking this with as much on as you can eg lights and screen heaters if the alternator copes with this it sounds fine and i would put it down to a glitch or one of the problems you have had in past i was an aircraft electrician and my galaxy wiring gets me scratching my head sometimes i fitted an ammeter on my last car to monitor the alternator hth john
