07 & 08 Explorer "4x4 Auto" operation
 

Can someone explain the "4x4 Auto" operation. Are there any indicators of the mode status like there is for "4x4 High" and "4x4 Low". Since there is a button for "4x4 Auto" on the console it seems you should be able to turn it on and off. But how do you know what the status is? On my 07 the 4x4 kicks in automatically on snow or icy conditions even without any action by me but the dealer service dept says the Auto mode resets to off when the engine is switched off. This does not appear to be the case for my vehicle. Knowledgeable comments on the proper operation would be appreciated.
Thanks,