Need help with with the ABS,BRAKE,DSC Lights

[4.4i_TOMATEROS]

I have a problem with my 2003 x5 4.4i with the ABS SYSTEM the abs,brake,and dsc lights came on a week ago. I notice that when i turn the truck off they go away but i turn it back on and everything its normal i drive it for 3-4 mins and and i hit the brake and the pedal feels realy stiff and when that happends the 3 lights turn on and when their on everything goes back to normal the brake pedal its normal and it brakes normal but the lights are on. Some people tell me is the abs speed sensors others tell me is the abs module please help