Is the regen light flashing? And or the check engine light on. Do you have access to Cummins Insite you can go to diagnostic tests and see the pressure diferential on the dpf and see if regen is needed, click on the regen test.
Could also be a number of ECM codes inhibiting the regen, anything from wacky sensor readings to turbo VGT not responding properly. Need to scan for codes.
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