ABS issue

[61_FL_Apache]

This is actually for the wife's 04 Chevy Venture van... but its in the same era of vehicles and hope my question is not too far off.

Over the last few weeks, the brake pedal has been feeling spongy and the ABS light will come on. When its acting up, the brake will go further down that usual and you can hear the ABS pump running.. When the ABS light comes on, the pedal feels fine, but the ABS system is not active. I put a cheap-o code scanner on it, but there are no codes..

No recent brake work. Any ideas? To me it felt like a worn out master cylinder, but I don't think so now. 69k miles on the clock.

Thanks for your help!!