Don't forget to do the key switch thing--also If it was me I would put both sprockets back to stock and work from there-16 just might be to much for the ECM to handle-but may work with a 15 and stock rearI took the ABS fuse out and went for a long ride, stopping every 40kms or so and turning the bike off and on again.
The ABS fuse also services the speed sensor so that when disconnected there is no speed indication, and therefore no "range remaining", and the odo and trip meters are frozen. After 120kms I replaced the fuse and rode a further 60kms home. The fault and the check engine light will not reset.
I'm guessing that like other Versys the speed sensor works off the countershaft sprocket. My next experiment will be to go back to a larger rear sprocket and buy a 16 tooth front sprocket that I now know will fit.
I'll also disconnect the battery overnight.
p.s. the two fault codes displayed by holding the two dash buttons are 24 and 25.