You shouldn't need a scanner as long as you didn't let the master cylinder run empty. That can easily be prevented when changing components by using a stick from the seat to hold the brake pedal down about an inch. That will stop the brake fluid from running out.
If the master cylinder ran empty, there's air in the hydraulic controller. Many ABS systems won't let the air bleed through unless you use a scanner to activate some of the valves. Until you do that, the trapped air will compress and cause a mushy pedal. Some systems like Chrysler's Bendix-10 will bleed the air out automatically when the pump runs.