First thing you need to do is have the systems computer scanned. This will help us understand where the problem is, so we can properly diagnose.
Some auto part stores will scan for FREE or offer tool rental or loaner programs (Autozone and Advanced Auto Parts)
If you have any questions just ask
That light being on indicates that the control module has recognized a problem. It then stores a trouble code for later retrieval and disables the system as long as the light is on. Your first step is to locate a shop with scan tool equipment capable of accessing the codes. Those codes will get you pointed in the right direction to find the problem.
Unfortunately, this is not one of the free services provided by auto parts stores because the inexpensive, generic equipment they use is not capable of reading ABS or Air Bag codes. This requires an expensive, professional scan tool.
This is generally an electric issue that doesn't effect the normal hydraulic braking of the car but the safety feature of ABS brakes will be disabled whenever the light is on.
I made a misstatement by saying they will scan for free, but some stores rent scanners able to read ABS you may have call around to find them.
I apologize for this.
The vehicle will still need to be scanned to identify problem
These code readers at these parts stores WILL NOT read ABS codes in that vehicle.
If can't get communication with the ABS module, then either you are still not using the right equipment or the module itself is dead which could be your whole problem.
Check all your fuses and make sure the equipment your using has updated ABS software capable of communicatiing with the ABS module.