Quote Originally Posted by NomakeWan View Post
I'm not sure what you're trying to say. The diagnostic pin is already 12V (through an internal pull-up resistor). The only available option for this pin is to ground it, which puts the CCM into diagnostic mode. Here is the relevant section from the FSM. It also addresses spfautsch's earlier comment about some CCM-related DTCs not setting the SYS light.

ccmdiagnosticmode.jpg
Yes, I understand and I will post my GM documentation when I find it. The Mefi4 is very very similar to the obd1 LT1 computers electronically and when I need to convert a 4 into a 4a or 4b this is how we get it into boot mode for programming the entire 256k and not just the calibration data, and yes, still ground for diagnostic mode. Maybe this doesn't work on the LT1 computer but I bet it does. I only have obd2 LT1 puters here or I would already know :)