Side Mirrors Defrost symbol never lights up

[Dacflyer]

My 2013 TC XLT has the defrost icons on the mirrors but they never light up.

Does my van have this option ?

If it does, then when does it activate ?

It does not seem to work with the defrost button for the back windows.

there's been frosty weather many times already ( below freezing ) If the van has this,,are they automatic ?

I'm guessing that if the icon is on the mirror, then the heaters are there also,, So maybe there's a relay or module i can just add in somewhere ?

[MLB]

My 16 rear defroster never worked. my 16 xlt has no mirror heaters but no defrost icons so i would guess you do.  I'm thinking I read it was tied to the rear switch.  Could be a blown fuse too since it heats it's a decent draw. 

[Dacflyer]

I found out, that I do have defrost mirrors, but there's no indicator that lights up for them,

and the switch is connected in with the rear window defroster switch.

I just had to wait til it was cold enough to find out..

[mrtn]

We have had mirror defrosters since the beginning of times over here and there has never been a separate indicator for them, in any car. Mostly it's just the rear window defroster light (as they're always combined) even in cars that don't have rear windows (such as my cargo vans), sometimes the button has two icons - rear window square + mirror but the dahsboard light only has the rear window.