GPCM testing

I’ve been helping a neighbor with a 06 6.0 with 150k that is having cold start issues. I there isn’t a CEL but I’m getting a P0670 on AE. So it looks like his GPCM is shot but is there a way to test it? The previous owner made a mess with some of the wiring so I would like to make sure it isn’t a short before my neighbor drops $150 on a new GPCM. Also, are there any tips or tricks to testing the glow plugs? I’m a 7.3 guy and know little to nothing about 6.0s.

Yes you can test the glow plugs and the glow plug control module with ease. Just keep in mind the wait to start light and glow plug on time are independent of each other. Meaning if the light is off, it doesn't mean the glow plugs are off.

Disconnect the 4 pin connector at the valve cover. Measure each glow plug resistance to battery ground, the glow plugs should fall between .1 and 2 ohms. Then measure the engine harness resistance to the GPCM, those should fall between 0 and 1 ohms.

The GPCM and the glow plugs are pretty stout in the 6.0's though, rarely is there an issue, but being you have a code it's a good place to start. I would also verify that the batteries are in tip top shape before testing anything though. Have them load tested, if one is bad replace both.

If the batteries check out and the Glow plug system checks out, test the FICM.