My brakes lately have been feeling pretty weak. Today I was coming to a red light, and I'm putting more pressure than usual to stop, when suddenly the pedal goes all the way down with a sudden click, and the red brake light shows up. I checked the fluid, only to find it was almost empty, so I bought more tonight and filled it up. No change though. The light is still on, and the brakes are still weak. Anyone?

 

You need to bleed the system. There is a shuttle valve in the ABS module that tripped the light.

 

If any air did get in the system, yes, you need to bleed it. If the light stays on after bleeding, stand on the brake pedal hard until you hear another click and the light goes out. The pressure differential switch will then be reset.

 

Make sure the "click" you heard wasn't a flexible brake hose (leading to the calipers) breaking. If so, it's going to be leaking fluid (big time) and will need replacement.

 

If you found the master cylinder was "almost empty", take the time to inspect the entire system for leaks.