This is an introduction post for those that don't have GM scan tools. You can get the clone MDI for around $200 and a clone Tech 2 for around $350 or $250 without the case.
If you don't have a Tech 2 I would just get a clone MDI and a cheap garage laptop or build a PC in a cart with fans and air filters and a small flatscreen under tempered glass. A laptop is portable but an old dual core PC is likely free. You can build a cart out of plywood to house a full tower and just swap a dead PC for another.
If you have an older car with unknown PCM history it may be a good idea to save the PCM contents with HP Tuners or the like and then update the PCM-ECM with the GM tool to the latest bone stock calibrations. You can read the PCM contents using HP Tuners without licensing the PCM. I would not license the PCM til you complete the SPS updates...
I would be remiss if I didn't make this comment. This is my understanding of the situation.
Be Aware: HP Tuners says you're using credits to license an individual PCM to your HP Tuners tool. That's not a completely accurate statement.
From multiple posts by HP Tuners mods and staff... It looks like they use some kind of hash of information from the PCM processor and PCM Operating System and possibly other PCM software and hardware and maybe the VIN to come up with a serial number that you are actually licensing.
If the PCM gets updated using AC Delco SPS... It could void the licensed credits and HP Tuners could require that you purchase new credits for your already licensed PCM. They get more than a little prickly about anyone questioning this. I've read about at least one instance of a dealership updating a PCM when the vehicle was brought in for service and the owner then had to buy new credits to tune the PCM they had already licensed.
My guess is that most PCMs and ECMs may-not/do-not have a unique electronic serial number and HP Tuners programmers came up with a work around that works 98% or 99% of the time. They tell the 1-2% that have problems with this work around to buy more credits or pound sand.
So far I'm in the 98% but it's something to be aware of and be careful of.
AC Delco Account setup is free but you have to pay for Service Programming access... as of this writing Feb 2, 2019 the cost is $40 for 24 months single VIN Service Programming.
The Tech 2 requires a good quality RS232 serial connection. No device drivers needed in Windows 7. BTW DO NOT USE a USB to Serial adapter for service programming... most if not all USB to RS232 device drivers have signal latency issues that could cause you to brick the PCM or whatever other controller you're updating. I used a Quatech Expresscard-34 EXP34-SSPXP-100 (PCI-e) RS232 adapter in my old HP8560W Mobile Workstation.
This is the procedure for calibration updates with a Tech 2 in J2534 passthrough mode.
The same with an MDI.
This is a YouTube video of the procedure using a VXDiag Chinese J2534 passthrough tool. I'm leery of anything from China that requires me to install Chinese device drivers. A tool like this is no exception. IMHO A Tech2 or MDI is a safer choice.
I should've put this further back in the thread but I didn't have a good howto til I found this video group from Dr Shock.
If you don't have a laptop with a good Serial port... The WiFi MDI clones are pretty decent quality now. Get the high quality unit with the SQU WiFi card and load it using the MDI manager from Bosch... not the one that comes from China on CD. MDI manager straight from Bosch has un-molested drivers.
You can use the hacked version of Tech2Win that ships with the clone MDI but the Tech 2 is lighter than a laptop and runs from the vehicle battery and I already have one. The Tech2 will also talk to 1992-1994 ALDL and 1995 OBD1 vehicles. The Tech 2 costs more than the MDI and only supports vehicles up to around 2009 or 2010 with limited support for 2011-13.
The Linear flash card image BIN files that the SAAB guys put up on the Tech2WiKi
will work with the MDI and Tech2Win on 1996 and newer vehicles.
I have both a Clone WiFi MDI and a Tech 2. I just bought the MDI. I've had the Tech2 for several years.