92 Lesabre -ABS light -wheel Sensor

Hey guys,
Great information on the site. I am a newbie to the forum.

My wifes ABS light is on fulltime. It came on after the rear wheel cylinder blew out and she drained all of the brake fluid. I replaced the wheel cylinders however the light won't go off and the ABS is now disabled. My GM Code reader won't give me the ABS codes so I don't know exactly what it is or how to clear. I took it in for a diagnostic to get the information and the guys told me I need new ABS Wheel speed sensors ($315 each before labor). Is this just a coincident or am I about to buy something I may not need. Is there a way to clean up the wheel sensors since they're just Hall-Effect units and reset the code. I don't know how to reset the ABS code to get the ABS back working.

Thanks in advance

When scanned for codes and/or driven they can look at comparitive wheel speeds to pinpoint which sensor is not showing any input, seems odd right after your work they both went bad? rear as you did not say which ones, info here is lite.

Sorry on the info being lite. The local mechanic said the front wheel speed sensors needed replacing. He did not elaborate any more than that, I assumed he ran whatever diagnostics he needed to identify the problem. In the past the master cylinder reservoir ran down below the recommended level and the red BRAKE light would stay lit. This time that light did not come on but the ABS light came on. She used the brakes until she forced all of the fluid out of the system. The guy said nothing about any sensors in the rear wheels he was specific and said the front wheel speed sensors need to be replaced. If there is other information that is need to supply I can gather it but I don't know what else to post.