I bought a Chinese clone Tech 2/GDS2 MDI on vxdiagshop.com for $115. I can sub to GM’s TDS for SPS programming for $40 per VIN at 2 years. As a Tech2 clone w/CANDI module and GDS 2 software (what our cars use) it works great. Have set it up on Win7 32bit laptop. Tech2 works fine, but our cars don’t use it.
As far as i know GM doesn’t check what hardware/software you are running. I can use the hardware you purchase and subscribe to the SPS, but there is no way to get it ‘free’, as everything is held on GM’s servers.
GDS2 allows me to test and monitor every module on the car. I have a window issue and it allows me to roll up/down my windows from the laptop. Other things I have played with are holding specific RPM while checking sensors. I mean you can do anything – activate wipers, squirt washer fluid for enjoyment, reset steering angle, relearn HVAC blend doors, relearn and adapts for TCM on auto trans, activate ABS module for bleeding – anything with a module can be remotely activated and tested via the GDS2. Anything a $4000 Snap On handheld can do the GDS2 software can also do. It’s powerful stuff – Especially for $115 and time to set it up.
Overall I suggest doing as much research as possible for what your needs are as there is a lot to learn here. I bought the VXDIAG VCX Nano because it best suited my needs and was inexpensive, but there is a bit of a headache to the setup. Some others are easier to set up and look like official GM badged units (MDI/MDI2) but cost more. Take your time if you decide to get into this and research as much as possible. Just remember that its not only the ability to program modules, but you also get a full diagnostic setup for any GM vehicle that supports Tech2 and GDS2.