I have AUI Fairlane with ABS/TC. The abs/tc light come on when I roll. I am assuming its a wheel sensor.
I have recently changed Module due to other problem.

Any ideas on how to self diagnose it without plugging it into a handheld?

there isnt a way. obviously visually check all the wheel speed sensors and visible wiring for damage, but you really need a self test..

Did visual and wiped down sensors, still the same..
Is there a way to test the sensors one by one?

Turns out the ABS module (the replaced one) was faulty.