The ".c." on your Tekonsha Prodigy P2 Trailer Brake Controller # 90885 is not an error code but rather is telling you that a trailer is connected and your boost is turned on for the controller. From this is does not appear that there is a problem with the controller.
If the ".c." is always on even when you are not connected to a trailer then it would appear that the blue wire has a short to ground in the wiring. This may be at the connector or virtually anywhere in the wiring harness.... view full answer...