I have tried to locate it as you said, behind the grille, but it is not there. Is there another place it could be mounted? I have looked everywhere.
ambient air sensor location on 2004 Chevrolet Blazer
Behind the center of the grill on the hood latch bracket. Black plastic with wires attached, of course. Remove grill, if nessessary. May be able to position grill as to access, but best to just remove it. Do you have a replacement part? If so just look for the same thing!!