ABS without function – lamps Check OK – then off again

Hello people, with my 2,8 year 94 the ABS doesn’t work. If I fully enter blocks everything completely! The ABS indicator light lights up when starting – then goes out again. Read out error memory and ABS Stg. check are in order and without error, when reading out the control unit the lamp flashes then in AI briefly. Can’t that explain to me? Normally, should the lamp in AI light up permanently when malfunctioning?! Can you not manually test or run the ABS “pump” or ABS block as always the part means? Talk to 12V and see if it’s rammed? Because it can’t be on the ABS sensors, if an unplausible value would be delivered or none would occur at all when interrupting then a mistake would occur?! Slowly, really, and shortly before bringing the box into the workshop… Greetings