This chassis uses the sensors I pictured above on the two front wheels. There's a "Left" and a "Right" and they cost nearly $100 each. The rear uses a single sensor on top of the differential housing and it looks like this
It's easy to replace and Autozone (source of the sensor pix I've posted) sells it for $13.
The thing "looks" at one of the gears inside there, and over time, the metallic "dust" from normal wear will stick to it and trigger an ABS warning.
Top center of that big axle housing. Your tools are a can of spray brake cleaner, a 10mm wrench (socket is best) and a rag. Clean the area around it, remove the 10mm screw (through the tab in the pic above). Wiggle it a little and lift it out. Wipe clean and re-install.
If I had ABS warning I think I'd buy a new copy of that cheap part and simply change it, but lots of time it's just that metallic dust.
None of those sensors will keep your coach from moving.
I've been thinking you have engine running, park brake off, trans in drive. And that you can tell the trans is actually "in gear" and trying to move the coach. True?
