Is 15 volts at the alternator normal with no load on a 2003 cummins?

 

I don't know much about how the CTD are designed. However, It's not out of the question. If anything like gas brothers, The regulator is located in the ECM. And the temp sensor is used along with line voltage to monitor and adjust the charge rate. Therefore your regulated voltage can vary depending on the need to keep the battery charged. So 15 volts is not out of the question depending on your batteries state of charge.

Of course thats under the assumption they used a similar system for the CTD as they did with gassers.

 

i know on my gas truck is ussually suposed to be around 14 and i want to say no more then 17 mot for sure on that though

 

Sounds a trifle high. I wonder if one or both batteries is going away and the alternator is trying to compensate.