Lets isolate and chop the system in half.
Grab a multi meter, and lets look at the starter relay.
1. See if the signal gets power when you turn the key. I don't remember if it's switched power, or switched ground. Will be easy to check. Switched power = 0v on pin 86, energizes when start. Pin 85 will always have continuity to ground. Switched ground = always 12v on pin 86, open-circuit to ground unless start command. You'll also want to validate that pin 30 has power. This should be always 12v.
If all things there check out, issue is downstream. Check starter, solenoid, wiring, grounds, etc. And I mean check it. Don't load up the parts cannon quite yet.
If it's not receiving signal to switch, 3 things I'd look at next.
2. Check passlock / key / whatever the thing GM uses is. Can get more info later if ya can't find on google.
3. Check P/N lockout. Seen pinouts there, and on ignition switch
4. Check the ignition switch itself. Need to pull the steering column plastic off and start probing pinouts.
Between all of those, should be able to start to hone in on what's sad
Also, for the OBD not reading - it's a shared fuse with one of the interior 12v outlets. Don't remember which one.... But sanity check those are good