you can "interrogate" the modules, ABS including for errors using GT1 or INPA... not sure how to bench-test them - what probably is happening, the cold-soldered joint points have come loose, giving you the grief... the repair facilities fix that...

what you can test, is the diodes in the hall-effect sensors - right there at the plug at the wheelwell you put the tester and test the diode... if the sensors are good, then test the line from the wheelwells to the ABS - hint: to skip the line testing, do the test right at the ABS plug - if the diodes are good, you have good sensor and good line... if the reading is bad, then you go deeper...

if the lines, diodes are good, it leaves you with the module... you can repair it yourself but it is a serious PITA - easier to pay somebody to do it for you... and testing of the module - i would leave it to professionals (not the dealers!!!)