Freightliner Free help line may be able to answer your question.
Have your serial number handy, when you call.
The code info will eventually be dropped from the engine controller memory. The usual operation in automotive is, after the light comes on , if the problem is not detected on the next 15 engine start-ups, the light is turned off, then after approx. 200 start-ups the info is dropped.
I can't get the flash info from my Cat's ECM. Your Cummins may allow the retrieval of codes by the flash method.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.