What does it mean if the DTC status shows 'History (Not Present)' vs. 'Present'?

A 'History (Not Present)' fault means the DTC occurred previously but has since been cleared and is not currently active. A 'Present' fault means the DTC is occurring at the current time and the issue is active. If the fault is intermittent and not present, it may be caused by the PCM memory not having been cleared. (Page 7)