Ram Cummins Malfunction Light - Needed new batteries

You were lucky to go that long on the batteries. I think that is what you learned. Learning is good.
chevman

If the CAN bus senses a low voltage condition for a specified period of time it can trigger this fault. It's not really intended to be used as a battery diagnostic, but bad batteries can cause it to set....

Had a similar situation with our 05, since the batteries were replaced (one was pooched)the light has not come on.

sch911 - I agree that it was sort of a coincidence. I was going to replace the batteries anyway. I figured I was on borrowed time.

Would you happen to know if the error codes in memory ever go away? I am thinking that maybe they do not. I still had an old Emissions error code in memory from a previously fixed problem. I was told that after "X" number of starts, with no problems detected, that any old error codes are erased. But I'm not too sure that's really the case.

The code will be stored but not active for a number of starts, around 100~150 IIRC. After the tlight goes out it will pass any emissions test.

My batteries also lasted seven years before I replaced them. It seems to be the average life of diesel starting batteries that sit under the hood with that engine heat.

My '04 CTD threw a code after the battery went dead and I had to get a jump start.Once the battery was charged up the code went away.
No need to go into what caused the battery to go dead.:)