ABS light on/off

I'm sure everybody's heard this one before, but I have to ask again.

I have a '01 venture and after starting, sometimes the ABS light does not always go off. (when light is ON wheels will lock up under hard braking or slick roads)) I took it to the dealer and they couldn't find anything wrong(light wouldn't come on.) This van is not equipped w/traction control. I have checked the wires and the connections at the wheels, and everything looks fine :confused: ....any suggestions or help would be appreciated....thanks

My ABS light has come on twice now.
Last year I needed a brake job and last week a bearing.