There have been reports of inoperative remote engine start (RES) fobs in 2017 and later Subaru Impreza vehicles. The blue LED does not illuminate when pressing the start button when installing the RES accessory. The cause of this is a dead battery in the fob itself due to a software issue.
The repair for this condition is to order a replacement gob, P/N H001SFL020, which has the updated software. In addition, RES kit P/N H001SFL001 and H001SFL101 include the updated fobs.