2017 Nissan Altima — coolant slowly disappears without an obvious leak

Log the conditions before you spend. Swap the cheap/easy piece first on the 2017 Nissan Altima and see if the fault moves. Save the big job until that test fails. On “coolant slowly disappears without an obvious leak,” that was the fork that mattered for me. Happy to compare notes if your setup is different. Not driving it hard until I know more.

OP update: scanned the 2017 Nissan Altima again and still only have the one pending code, no new lights. I refuse to clear codes until someone else sees them.

Cleared nothing. I want service to see the alert on the 2017 Nissan Altima first. Might be overthinking it, but I'd rather overthink than overspend.

Ask what changed right before it started. Write temp, speed, and in-gear vs coast when the 2017 Nissan Altima does it — then decide on parts. That's the branch I'd chase this week. I'd want a dollar figure or a measured spec, not 'should be fine.' I'd rather look cautious in this thread than stuck later.