The ABS module controls the speed input for the speedometer, the odometer incrementation, and the ABS system. Failure of this module is a particularly common problem on these specific vehicles. The common failure symptoms are: Odometer stops recording new mileage, speedometer does not register above zero, ABS light and BRAKE light are continuously lit. The traction control lights may also be continuously lit. Failure of just the module will not throw any codes that can be seen or read with common scanners.
The module is located under the dashboard, above and to the left of the brake pedal. There are two screws that mount it, one up and to the rear, one lower. It is easily accessed by looking up under the dashboard. The upper screw in the back that goes into the firewall is harder to access, but it isn't too difficult beyond a little reaching.
Unfortunately there are no easy troubleshooting methods of this module for the shadetree mechanic, other than checking that it is recieving power, fuses, etc. So usually it is either a process of elimiation, or a rough guess. The cheapest way to check this is with a known working module, by swapping the two and checking funtionality. If all symptoms are resolved after the swap, then the original module is bad.
Just as an interesting note, disassembly and a quick check of a failed unit showed no physical issues like bad solder joints, easily identifiable bad components (such as melted or burned), or failed circuit board traces. So we imagine that while these units are fixable when bad, it isn't something that the average person with simple equipment will be able to do easily.