OK, Alan. So, Jon-P, assuming that the CS2 will read CVs, I guess the first thing would be to put it in programming mode (however you do that) and try a readout of CV1; if you get a result, then that will confirm there is a decoder on board and also tell you what loco address it is on (so you'll know how to operate it in future), if you don't get a read of anything then there probably isn't a decoder in it. Please note that this advice is offered WITHOUT much knowledge of how the CS2 works, that's just how I would do it on my Massoth system......
Jon.