I had abs light constantly on my dash on V6, checked all abs rings/wiring etc and no fault code coming up with dianostics. This usually means (as it did with mine) a faulty abs pump/unit. If the pump itself is faulty it can't send a fault code. With regards to bleeding the abs system after putting in new pump, it can be done diy without a garage comp which is the way I did mine.
You basically bleed the brakes as normal to remove all air bubbles. Then take car out and you need to engage the abs to force any air in the pump out into the brake pipes, so braking hard several times on a wet or gravelly surface is perfect. Do this and re-bleed as many times as you feel is necessary. Its obviously not as 100% safe as taking to a garage but alot cheaper!