ABS light on 1995 model

[jpliddy]

hi guys
are you familiar with ABS system on the 940 diesels light comes on when i switch ignition on and start car without moving and stays on volvo put these on later models as you know its a mot failure so hope its not terminal i don't want to go out and buy new sensors if its something big like the modulator or control unit
i did get a bit of a rattle noise a while ago on turning ignition on before starting i wonder if thats anything to do with my ABS can you give me any directions to go forward ?