I'd expect you to be able to retrieve powertrain diagnostic codes through the odometer window of your instrument cluster, despite failure so far.
Cycle the ignition key from off to on a few times and see what happens. It's sometimes difficult to hit the exact cadence needed to display DTCs, so keep trying with different rates of cycle. Turning the key completely off while cycling seems to aid in the effort with most of our vehicles.
When you get the right sequence, the window will change from displaying vehicle miles to (possibly) dashes and then will display P-code(s). Record the code(s) and write back. I may be able to help with the diagnosis or repair from here.