I have a long list of DTC codes (37 codes) but I cant tell when these codes occurred. Should I clear the codes and rescan to see what is current? My engine light is not on right now.

Do some codes stay on the computer forever and can't be cleared?

I am new to the use of the OBD2 scanner.

I hope to hear back from someone soon.

 

If the check-engine light isn't on now, that means none of them are happening at this moment. (Assuming the CEL bulb is OK)

I'd make a list of them for your own information, clear them, & see what comes back. Actually, clearing the codes is at the front of most troubleshooting procedures, to see which ones are happening now.