Garter carriage problem

Hi, I have a Brother KH-940 machine and am using a KG-93 garter carriage. I did a sample of 2×2 ribbing which went well and wanted to try a pattern, but for some reason the garter carriage won’t work. I’ve checked all the steps and everything seems in order. It’s like there’s no power getting to the carriage. Any ideas as to why that happened all of a sudden? Thanks for any help, Jill