2002 Chevy Astro ABS light wont go out

I checked the speed sensor wires to the transmission and they read 8.53 ohms with the motor off with the motor running I could not read any D.C volts to the sensor but im not sure if I am supposed to with it at idle or if the voltage is generated with the van moving the wires go back to the vehicle control module one wire is signal the other wire is return. Do you know if voltage is supposed to always be present?