GM data II serial radios explanation?

   I've been trying to find out more information about the new GM vehicles that come with so called data II serial radios. I have been reading different posts with different information on them, I was just wondering if anyone could explain a little better what is integrated into those radios, which GM vehicles do they come in, and what are the disadvantages (dangers) of removing those headunits?

    Also how could one tell which stereos have it? Are they the D-Din GM stereos and not the old Din & 1/2?

    I am an installer / inthusiast and I wouldn't want to make any costly mistakes so any inputs on this topic are greatly appreciated.

Here is a post from another forum that explains what is controlled and what is not:

Class 2 Data Vehicle Concerns
Metra's 70-2003t and 70-2003

Applications:
CHEVROLET - 2000-01 Cavalier, Impala, Monte Carlo, and Venture. 2001 Malibu
GMC – 2002 Envoy
PONTIAC – 2000-01 Sunfire and Montana. 2001 Aztec and Grand Am
OLDSMOBILE – 2000 Silhouette and 2002 Bravada
Note: The 2001 Venture/ Montana/Silhouette do not require the SP-2003 chime module.

Metra’s 70-2003t is a 15 foot “t-harness” that will allow the installation of an aftermarket radio while keeping the factory radio (somewhere accessible) in the vehicle to retain “vehicle customization”. This is required because the radio is used as a control panel to communicate with the vehicles computer for the customization of certain “convenience features”. All features work and remain at current settings with the factory radio removed, but can only be customized and/or reset by an authorized service center. In my belief, the door chime is the greatest loss, which is inoperative without using the 70-2003t in conjunction with Metra’s SP-2003 chime module (self enclosed speaker) mounted under the dash. This will keep the chime to its factory settings. Metra’s 70-2003 can be used instead, but the factory door chime will not work.
There is also no switched 12vlt. power supplied in the radios plug, so it will need to be sourced somewhere else such as the factory fuse panel. A 15 to 30 amp fused accessory power source is recommended. Depending on the vehicle there are several choices in the factory fuse panel, such as the sunroof or windshield wipers. Both the 70-2003 and 70-2003t include a 42” red wire with a fuse tap at one end.
Vehicle Customization Menu Options: (Most Cavaliers, Sunfires and other base models do not offer most, if any of these features. Check the vehicle owner’s manual to see available features.)

Displays current settings
Oil life monitor reset
Tire inflation monitor reset
Delayed headlamp illumination
Automatic door lock and unlock
Remote visual/audible verification of remote lock/unlock
Enable/Disable content theft
Enable/Disable trunk lock shock sensor
Short or long horn with remote lock/unlock
Key fob transmitter programming

For the Cavalier air bag concerns:
GM’s service document numbers 537803, 558212, and 558208 give detailed instructions
on removal of the radio. Document 537803 is the basic removal and installation referring to 558212 for the trim plate bezel replacement, and to 558208 for disabling the SIR system. Not suggesting things shouldn’t be done to procedure, but I‘ve spoken with a handful of GM service techs and not one follow these procedures when removing a radio. Do you disconnect the negative battery terminal before any install?
Other:
There is another group of vehicles using class 2 data. The Oldsmobile Aurora, Buick LeSabre and Pontiac Bonneville use a flatwire or ribbon cable type connection @ the radio. This is also referred to as GM’s “dock and lock” setup. Until a harness, in my opinion a complete rewire is easiest for aftermarket head installation. Cadillac also has several models using class2 but further info is not yet available.

Thank you very much Jeff I appreciate the info.

Also are the new 2003 Tahoes and Suburbans equiped with this head unit? Because, if I'm not mistaking, they have the same D-Din Headunits as the Cavalier does.

Thanks again.

Metra now makes a part that doesn't require the use to the T-harness (70-2003t) It plugs into the the harness behind the radio and provides the doorchime and and accessory that isn't in the harness anymore. This eliminates the need to run the T-harness through the vehicle and find a place to store the factory radio. I believe Metra is calling the adpater Vendeta.

Soundgate also has a similar part, that does the same stuff, This will make installing a new radio a breeze and cut alot of time out of the project.