When I push on the brakes they are fine until just before you come to a stop, then the pedal sinks a little bit and the abs chatter happens. I have replaced the disks all around and replaced the rotors all around. When I pulled the abs relay out, the light came on but the chatter went away. Could it be the relay is bad, and if so how can I test it?
The relay acts a switch to command the ABS system on or off.
The problem will need to be diagnosed by using a scanner. The scanner can detect where a problem is by setting a code.
The speed sensors can also be read while the vehicle is in motion to determine if one or more speed sensors are giving the correct reading.
That code(s) can direct the mechanic to the problem area.
Most common problem areas are usually the speed sensors and related wiring.