If you have a way to record the activity of the ALDL, you can use a Old Tech-1 or Tech-1A and record all you need to know. I placed a hidden function within the GM Powertrain cartridge but first I should explain. The Y-car and many others have a "Keep Happy Logic" with the Tech-1 comunications. This keeps all the controllers happy so no codes are set and you can still retrieve data from the ECM. What occurs is this. The Link is controlled by the Master. In this case it's the CCM (Central Control Module). The CCM runs the bus. Others are told (IF I remember correctly) when to broadcast their message on the link and then the next. Each few seconds you will find the "Master" ask a "FO" message. This is a "Hello is anyone there?" like the Tech-1 and you have a few milliseconds to respond. (You can see all this on the time stamp of your link recording.
Now If you monitor this with a Tech-1 communicating you will find the logic to keep all happy and the others controlling their systems. If you depress the F3 button on the Tech-1 using the Data Stream it will turn ON FAST DATA. The data link WILL SET ALL THE COMMUNICATION codes and all the children on the bus will be upset and default. BUT you will get the ECM messages at almost 100ms update rate. This Fast Data is for hi end users and for finding intermettant problems related to the ECM that occur at a fast rate and cause troubles. It's just another tool to have to help diagnose problem cars. The E-Cars had this Fast data hidden as well.
I did not include any Clear Codes option for any of the other controllers like CCM, ABS, SIR, ect....
I don't think the Tech-2 has Keep Happy. I was not part of the group when they back filled the prior models nor validated it. It is hear say. I do know the old 86-89 F/Y Car ECM 165 will not switch over to 8192 baud with the Tech-2 like the Tech-1 does with the E-Pin adapter.
I use to remember all this but fumes has been induced.