2002 2500HD 6.6 Duramax with Allison Transmission charging issue.

What is your question?

The lights flicker bright to dim the battery light came on but I checked the battery and its charging normal. I have heard about the ECM causing issues like this but I don't know what to test on it. The truck keeps clearing the codes before I can get in to see what they are. My engine light came on and by the time I got my scan tool it was gone and no history codes. After the truck cleared codes it ran great no flicker but this morning its back but no codes or engine light just the battery light. Any help would be appreciated!