ABS light comes on as soon as I am underway
 

As soon as I start in forward motion in my 2003 Silverado 1500 4wd, the abs light comes on and dings 4 times. I checked both the left and right sensor at the wheel and got 400 millivolts at each sensor with a vom when I spun each hub. I had the abs module rebuilt around 4 years. Could it be abad connection from one of the sensors to the abs module? I don't have a wiring diagram for the abs system, so I don't know which connections to check.
Also, is it normal for something wrong in the abs system to not a code in the onboard diagnostic system?

its seting a code but its a chassis code...a code reader won't access it...you need a full function scan tool that can read the ebcm.