I am having the toughest time trying to figure out my key fob. I'm driving an 03 Blazer. I bought a key fob off amazon that should work with my car. When trying to reprogram the car, i hold down the unlock button and do the turn key up/down/up/down and release the unlock button. NOTHING HAPPENS AFTER! My car does NOT respond and go into reprogramming mode (locks unlock/lock). I think the reason is because I have an after market radio/ head unit installed and the key fob receiver is in the original factory radio. Is this the problem?? Any help would be appreciated. Thanks