My 2007 FEH used to remind me to change oil every 10000 miles. More than a year ago I started carpooling and only use the hybrid on weekends or for long trips. My last oil change was in May 2014 and since then I have driven less than 6000 miles. Today the oil change reminder turned on.

I understand there is a time element in the countdown, but how does the car keep the time? Is there a clock somewhere? If so, does it have its own battery to keep the clock running when the main battery is disconnected? I don't think Ford would put a GPS chip somewhere to keep the time updated.

 

A circuit inside the PCM which is powered by your 12V battery all the time.

 

There is probably a "real time" clock in the engine control, or perhaps another part of the vehicle, that keeps time without any connection to any external battery. A $20 Casio watch can keep time for 5 years on its internal battery.

Still, you know the conditions where your car has been, and what oil you're using. It probably doesn't need an oil change.