Multiple glow plug codes

I'm working on a friend's 6.0. Truck has codes for glow plug circuit on cylinders 5, 2, 4, 6, and 8. So far I've tested the glow plugs and all of them ohm out at 5.6- 5.7 except one at 57 ohms. Last week I changed out #4 because it was at 51 ohms. At the time #4 was the only code. Pulled the connections off of the gpcm and the black connector has seen a little bit of heat on the big pin and a little of the plastic is melted. Still has good connection. Can anyone tell me if I'm looking at a gpcm problem or multiple glow plugs failing? I've read conflicting info on glow plugs saying if they are below 10 ohms they are fine and some say it should be .5 to 2 ohms.

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personally I believe that the 0. to 2 ohm range is what you want.

If you changed out #4 and it is still throwing a code, then that would point to the harness and/or the gpcm - at least that is my 2 cents.

Glowplugs should be less than 1 ohm to ground typically. You will need all thr glow plugs it looks like. Also do the harnesses, as they like to break when you pull them apart. Also check with a test light for voltage going to the glow plugs using the harness side to ground. If you dont have 12v, find the issue. More than likely the gpcm, but could be harness. I like to test glow plugs ans the harness with a test light, as it load tests the circuit. Do not use an led test light though, as they need hardly any voltage at all tooperate.

6.0 Tech said:

Glowplugs should be less than 1 ohm to ground typically. You will need all thr glow plugs it looks like. Also do the harnesses, as they like to break when you pull them apart. Also check with a test light for voltage going to the glow plugs using the harness side to ground. If you dont have 12v, find the issue. More than likely the gpcm, but could be harness. I like to test glow plugs ans the harness with a test light, as it load tests the circuit. Do not use an led test light though, as they need hardly any voltage at all tooperate.

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Got it. I replaced the driver side harness when I did head gaskets a couple months ago. Now you got me thinking it might have been .57 ohms instead of 5.7. I'll check again. I'm assuming when testing with a light from harness side to ground I need the key on? Or will it have 12v all the time?

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Yes key on, you have to do it before they shut off to. So maybe have a buddy turn the key on while you check. They will only be on a max of 2 minutes depending on temp.