| Possible to upgrade older OnStar?
I have been fielding a lot of questions lately regarding the ability to upgrade older OnStar systems.
The short answer is no, and here are the main reasons why, for those of you who are curious.
I believe OnStar started out in '96 as a dealer installed option with a handset. It was limited to specific vehicles, mostly the upper end stuff.
I believe in 1999 they changed to a 3 button design but it was still a dealer installed option and somewhere around 2000 or 2001 it became factory installed as a 3 button system or what we call VS-3B. (the handset is called VS-P)
As time marched on OnStar made changes here and there, usually requiring some sort of change in the vehicle hardware. As these changes took place and features were added they changed "Generations".
They have progressed over the last decade up to Generation 7.
The only way to get turn by turn directions (as seen on TV) is to have a Generation 7 equipped vehicle. This requires specific vehicle hardware and communications systems and I think that '08 is the first year the bulk of GM's fleet (maybe all but I don't know for sure) will be Gen 7 setups. But I digress....
Basically OnStar upgrades are a change from Generations 4, or 5 to a Generation 6 box. (maybe Gen 3, I forget the specifics but it is really not important) Even upgraded units won't get the turn by turn feature.
The problem is that older Generation systems used two boxes. A VIU and a VCU. In '02 they switched to a single box system which is called a VCIM. When the change took place the two separate modules became one with new connections, different vehicle wiring, and more features.
To clarify, the VIU is the vehicle interface unit, basically the vehicle side of the system. This is the box that has the GPS receiver in it and it handles voice commands and vehicle control. Such as honking the horn, flashing the lights and communication with the vehicle through the cellular device.
The VCU is the vehicle communicaion unit, which is basically a cell phone.
It looks like a tall whiskey flask really and it handles all cellular functions and gets data from the VIU for transmission to OnStar during phone calls.
The VCIM, or vehicle communication interface module, does both jobs internally.
Currently, and I don't expect any change, only a VCIM upgrade is possible.
The connections are all the same except for the GPS antenna and those kits come with adapter cables.
There is no real way to rewire the car to use newer hardware to make the upgrade possible, but even more impossible would even be ordering the kit.
You see, the first thing we do when ordering an upgrade is type in the VIN. If the VIN is not eligible to be upgraded then we have no way of ordering one. The VIN information and the modules are sort of "matched up" before the kits are even sent out so they can be activated quickly. The kits come differently based on the vehicle's VIN also. Some cars require replacement of the mounting bracket and other vehicle options may require a different type of bracket.
I could show you connector end views and wiring diagrams until you passed out, but suffice it to say, nothing matches up. The old VCU even uses an old style serial pin type connector. (I'll attach that one)
Sorry for the bad news, even if you wanted to spend a bunch of time and money trying to keep OnStar, you'd never be able to order a kit. | 
