07 dodge ram will not start

I have installed an astrostart 5224 with a xk-532 modual in a 07 dadge ram diesel last year.  I just recieved a call from the customer that the vehicle will not start via the rss or the key!  This unit has worked fine since i installed it and now all of the sudden not working.  The diagnostic code on the modual is 4, no tach signal.  The vehicle will not even crank over with the key.  Any help would be greatly appriciated-nosnvln-

I'm guessing that the transponder module on the truck is not recognizing the key therefore not starting the truck. That being said, did you isolate the mux wire with a relay? If so, relay might be bad?

Probably not the same, I went on a 4 hr road trip today for a no start condition.  After jump starting the car, everything worked.......... battery was dead.  Check all the stupid things, in park, factiry alarm disarmed ect.