Hi , Navistar is a GPS thing , as far as I know there is no Navistar radio it is satellite transmitted, International has recently began the sirus radio deal , ( as you know) so most likely International is connecting the three of them and there is a miscommunication that hopefully sirius can help you with , the customer service number is 1-866-635-5027. I would like to just be able to just let you know myself what to do but , I don't know where the Navistar fits in unless it is some kind of package deal . Good Luck ! Oh and I know my sirius gets knocked out by anything taller me , and everything is taller than me but it comes right back.
Just googled international and yeah , the three of them , Navistar , and Sirius have partnered , and International is a customer