I am working on a Pontiac grandam 2002. What is the best way to trouble shoot the abs system. ?

I have cleaned the wheel sensors. It is not operating at all. I was told to clean the electronic control unit how would I go about that.|||You can't troubleshoot those w/o a special scanner, the abs is on it's own computer (not OBDII). It is most likely a wheel speed sensor or bad connector, cleaning does not always work but is the best thing to try first. A shop will charge 30-60 to scan it, some transmission places perform free diagnosis, its the only way to find which corner of the car is causing the problem.