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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Tones H3:
There are a few Hummer H2 nav's for sale on ebay. Some of them do say that it would require the dealer to program it with the tech 2 scan tool. What exactly is this tool? I have heard it mentioned a few times. Thanjs </div></BLOCKQUOTE>

The Tech 2 is the main diagnostic tool for GM vehicles. It is used to pull codes, perform screen snaps of parameters, and to download calibrations and to program components.
With most of the computers running on the vehicle's internal LAN, all the computers talk to each other, and have to be able to recognize each other on the network, therefore, the ID numbers of components such as PCM, BCM, Radio, SDM, XM Receiver, VCIM (fancy name for OnStar), etc., have to be programmed into the system. (That was a simple explanation of the GMLAN system.)