Ed,
The ABS sensor is located in the steering knuckle (front) or axle flange (rear), about 2 to 3 inches from the center and on most coaches, it is necessary to remove the wheel and sometimes the brake rotor to service it. However, you can check the sensor wire and connector (small, very flexible, and usually black) to be sure that it has not broken or become disconnected. You problem with checking the wiring is that you do not know which wheel to check (there is a sensor at each wheel) without the ABS trouble code and a code description, so you would have to check all wheels, and some are difficult to access.
Gerald