I've performed a Gen 4 to Gen 5 NAV conversion in my 2006 GS. All pins are in the right location all connections are secure. All fuses are good, when I turn it on there's power to the screen, it boots up with the lexus logo and goes to the fuel consumption screen. I press nav and it says "external system is not connected" I try to turn on the A/C and I get "check the connection to the air conditioner". Could it be an ECU like the gateway or body ECU? I even switched back (just the screen) and got the same messages. Since I know everything is done correctly (except possibly fry an ECU) what could be the issue before I take it to the dealer? Also I've already searched this forum on other lexus models, no true clear answer, I doubt that all these features are inop at the same time by coincidence. I also disconnected the battery for an hour. Thanks for your help.