Odometer

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In some vehicles, it is easy to obtain another BCM from a junkyard with lower mileage, and install in your vehicle. Newer ones require a Tech 2 to program it to the system.
The H3 BCM, is one of GM's latest models. It cannot be swapped from one H3 to another. Once it is programmed with a VIN, it cannot be programmed to another VIN, unless it is erased by the manufacturer or their repair facility.
And all the computers, including the radio, XM, Onstar modules talk to each other and check each other out on the serial bus.