I have a California 2001 F-350 7.3 turbo, recently replaced both batteries, both were over 5 years old, and was still having start up issues. I checked what i thought was the GPR and replaced it with a new GPR. I now understand it is an AIH, and now the issue is it still will not start after sitting for a day or so because the batteries and running down. I have to jump it to start. when i check the batteries they are at 12.5 v, when i go to start they run down to 8v to 9v What I have I done? I replaced the AIH relay because it was cracked and now I understand that it has nothing to do with starting? Is the GPCM Bad? how do I test the GPCM?
Thank you

 

There is no way to test the GPCM. If it was bad it would throw a code and set the check engine light.

If your batteries are dying it is not the GPCM, it is a drain somewhere.

There is a test for this, I cant remember exactly, but I think what you do is pull one fuse at a time and check for voltage on each circuit one at a time.