Press the AUX input button on the head unit several times. Does the radio LCD cycle between AUX, SAT1 and SAT2? If it does, you have the factory Sirius receiver. Depending on how long it's been since the subscription expired for this receiver, you may hear a promo channel loop (184, I believe) playing on SAT1 and SAT2, or get an "Unsubscribed" message on the radio LCD instead. To get the electronic serial # of the module necessary to subscribe to the service, while on SAT1 or SAT2 press the Menu/OK button near the lower right corner of the head unit, then use the rotary Enter knob to scroll down to "SAT Info". Press the Enter knob and the ESN should display. Write it down and call Sirius to activate, or you can do it online.