18 Ram 5500 6.7 L P0626

Hi I have a 18 Ram 5500 6.7 L setting P0626 and not charging the batteries. I installed a reman alternator and it worked for about 5 min then set P0626 again and is not charging again. I may have a defective part but how do I prove the PCM regulator is working like it should? I have 2.5 v on the field control wire when it's plugged into the alternator and the truck is running but I expected it to be a digital square wave signal and it is not. I am having a hard time finding solid info on how the regulator controls the alternator. 

P0626 Set Condition:The PCM detects that the (K20) Generator Field Control circuit is open or shorted to voltage.


Check the integrity of the (K20) Generator Field Control circuit:

 

 

Thanks for this Chad. I do have Alldata and was able to get much of this info there. I guess I'm wishing to know what the field control from the ECM is supposed to look like on a scope. -Brian

I'm sorry but, I don't have/know that info but, I would assume it is supposed to be a square-wave, too.

The field control will look like a power side switched square wave. The more the PCM wants the alternator to charge, the more pulse width it supplies.

For testing purposes, you can install a turn signal bulb in place of the alternator. One wire on the bulb goes to the field circuit, the other to ground. The PCM should easily be able to light the bulb. Use the scan tool bidirectional test for the alternator if it's available.

If it can't, then there's a PCM or circuit problem. If it can, then there's an alternator problem.