Yes, ABS is a Scrabble word!

Letter values in Scrabble US: A 1, B 3, S 1.

Is it a valid word?

ABS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

any of a class of composite plastics used to make car bodies and cases for computers and other appliances
a bachelor's degree in arts and sciences
the eleventh month of the civil year; the fifth month of the ecclesiastical year in the Jewish calendar (in July and August)
the muscles of the abdomen
the blood group whose red cells carry both the A and B antigens

Also: acrylonitrile-butadiene-styrene, bachelor of arts, artium baccalaurens, abdominal muscle, type ab, group ab.

Not playable in Scrabble US: AV.