Over time, the relay contacts become carbon-ed up. You can either change the relay with a new one or cut the top off carefully and pinch a thin business card between the contacts and draw it through there until no black trace comes out onto the card. Do not use abrasive paper or a file. I believe the relay is located separately from the pump, so changing the pump won't fix the relay issue. I used to repair ABS modules ... they blow the earth track internally as a very common problem; an easy fix. Failing that, it can be the ABS computer, but I'm assuming they checked there was a good signal to the relay first.