5901 antenna upgrade

So, in my 2002 wrx I have installed a 5901 with what I am assuming is the old antenna. Everything for the past two years has been working just fine, and I'm very happy with the system, so far. Just starting yesterday, my alarm no longer responds to any commands from the fob. The valet/led combo switch will not perform any functions either, and the led never turns on or blinks. I have the "turbo timer" feature installed, and when I push the switch it works just as it should. I've tried a new battery in the fob, and disconnecting power from the unit, and neither made any difference. I tested the antenna wire at the button, and have ground on the blue and black wires, and about 5.5 volts on the red wire. The other wires have no reading. At this point, I'm assuming I have a bad antenna, based on what I've read so far, but I don't know what antenna I have, or what the upgraded antenna would be (model numbers). If any of you know what antenna I need, or have any other ideas to try, I would be grateful.

Thank you,

Chase