Specifically methylates the N4 position of cytidine in position 1402 (C1402) of 16S rRNA. cytidine(1402) in 16S rRNA + S-adenosyl-L-methionine = H(+) + N(4)-methylcytidine(1402) in 16S rRNA + S-adenosyl-L-homocysteine Belongs to the methyltransferase superfamily. RsmH family.