What do you mean by "retaining" TMCC signal. If you mean they don't respond, it can be a few different things.
The R2LC is a small square plug in board that is the does the command and control and has the radio receiver. The antenna is usually a thin sheet metal piece attached to the shell of diesels with a wire that is soldered on and plugged into a connector on the main board. If the antenna is disconnected or if the radio receiver on the R2LC is not sensitive enough (or out of tune) the engine may not be able to pick up the commands.
There is also a program/Run switch. Is that in Run?
The first thing to do is to reset the R2LC with the proper engine code (in your instructions. Maybe an 8. Than retest the engine. G