Thanks for the feedback @ Chris on GM Tech2. Here share the problem he got trouble in and offered the corresponding solution.
I received the tech 2. Thank you.
But, when I connect to obd2, it says “cannot detect CANDI module, please verify module is connected”. If it helps you, the green light on the candi module is flashing (not solid). I am not sure what to do. Can you help?
I think I selected the wrong engine designation (there are 3) for my truck and the tech 2 could not communicate
because it was looking for a controller that was not present (which presented the error message “no candi module”).
So, I think the tech 2 was OK.
It was my fault in my selections. I got it to work now!