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Discussion Starter · #1 ·
Hey, so I’m getting a p0672 and p0676 glow plug circuit fault following replacement with 4 oem glow plugs and oem wire harness

I just removed and re torqued all 4, lubed and re seated the plug harness … cleared the codes and after two cycles of KOEO the codes came back.

Could the plugs be bad or would this point to the harness… or something else ?

I’m gonna take em back out and re clean the contact points while I wait for a reply.

Thanks


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You could spend the time to ohm out the new harnesses and engine harness at the module. Or you could ohm the old glow plugs and see if they are in spec. I did all of that and it all checked out and replaced the GPCM and the codes went away (I had 3 glow plug codes on the same bank)
 

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Hey, so I’m getting a p0672 and p0676 glow plug circuit fault following replacement with 4 oem glow plugs and oem wire harness

I just removed and re torqued all 4, lubed and re seated the plug harness … cleared the codes and after two cycles of KOEO the codes came back.

Could the plugs be bad or would this point to the harness… or something else ?

I’m gonna take em back out and re clean the contact points while I wait for a reply.

Thanks


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And what do you mean by "lubed" the harness?
 

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Discussion Starter · #4 ·
So swapped the glow plugs with new ones out of the pkg and that didn’t change anything so it must be the harness

When I first installed this only number 2 was an issue. About 200 miles later number 6 and number 2 were faulting.

Lube I meant I greased the o ring so it slid down so I could taken out of need be w/breaking.


I’m bad w electrical diagnostics so I’ll have to YouTube how to ohm the connections . I didn’t have this issue with the old harness or plugs so it must be the harness.


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What you can do is ohm the glow plug. Do this by taking a multimeter set to the omega symbol and, with the glowplug out of the engine, touch one lead to the tip of the glowplug that the connector goes into, and one lead to further down the plug. If the glowplug is still in the engine, touch one lead to the tip the connector goes in and the other to the ground. Once you do this, you will get a base ohm reading hopefully within the spec on the website I sent. Now you will do what the website says to do. Touch one lead on your battery ground and the other into the glowplug in question hole on the module connector. This ohm reading should be the same or within .1 or .2 of your original value. If it is the same or within that original, your harness is good. If it is different by a lot, your harness is shot along the line and will need further testing to isolate the glowplug harness from the main engine harness, I hope that made sense. If not, let me know and I can give you a more detailed explanation. My retired father had to run me through this as I am clueless when it comes to electrical diagnosis The lube on the o ring is a good idea, but I would think you won't break it as it hasn't gone through thousands of heat cycles.
 

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Another thing. Test the ohms on the multimeter. Touch the two leads together and see what you get. it should be very small, like .1 or around that. I spent a few hours chasing my tail because my multimeter was reading ohms entirely wrong.
 

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Discussion Starter · #7 ·
Thanks a lot, this is a huge help, made sense. I’ll go back out n try it again after I warm up


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Since your truck is the later 6.0, it is probably your gpcm. Sometimes they pop codes that don’t make sense. Mine went shortly after I studded with new glow plugs. Someone on here pointed me toward the (expensive) gpcm, and my problem was solved


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Discussion Starter · #9 ·
Since your truck is the later 6.0, it is probably your gpcm. Sometimes they pop codes that don’t make sense. Mine went shortly after I studded with new glow plugs. Someone on here pointed me toward the (expensive) gpcm, and my problem was solved


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Hmm I was thinking the computer phew lol. Yeah I guess I mind as well swap the glow plug module too just to freshen it up

Now that I think about it the cyl 2 code was before the swap of new harness so that could very well be the issue after all. Thanks for the info guys. I’m gonna test the harness for giggles but I’ll order a new control unit too


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Hmm I was thinking the computer phew lol. Yeah I guess I mind as well swap the glow plug module too just to freshen it up

Now that I think about it the cyl 2 code was before the swap of new harness so that could very well be the issue after all. Thanks for the info guys. I’m gonna test the harness for giggles but I’ll order a new control unit too


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I replaced my gpcm when I got a code and replaced the glow plug, but got another code. Following advice of someone on the org, I got it solved.


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Discussion Starter · #12 ·
Ordered a new GPCM which I can go pickup tomorrow. I ohm tested the harness and it "seemed" fine so ill check back tomorrow.
 

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Ohm test by it's self can mislead you -- you need to load the circuit and check voltage drop across your power supply

Problem with modern ohm meters and analog circuits is, the meters are too sensitive

One single strand of a wire in the glow plug harness will ohm good, but will not power a glow plug
 

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Discussion Starter · #14 ·
I replaced the GPCM and now I have more bad glow plugs codes 2.6 snd now 4… … I reseated all of the connections so now I’m gonna re ohm everything. Suddenly It seems I have more codes than before for other crap .. such as ebp, egr , map etc. that was not present prior.

Talk about frustrating ….




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They all seem to have the v-reference circuit in common (except the glow plugs) ........
 

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Discussion Starter · #16 · (Edited)
So by measuring at the black connector unplugged from gpcm…. Your link states .5-2.0 ohm in spec

2- .9 Ohm
4- .9 ohm
6- .8 ohm
8- . 9 ohm


Before I took the black connector off the gpcm I took the connector of the harness off gp 2, measured the neg to battery grnd. Then power to connector I got nothing 0 ohm. Then the power to Cyl 2 GP in the truck was .5 -.6 ohm:

Seems the GP black connector connected to the GP harness and GP shouldn’t be different from the gP 2 to ground number ? Isn’t that the same reading ? Per the instructions. Im kind of at a loss.

Edit again : KOEO: voltage is 11.69 volts at the glow plug 2 connector and 12.47 at the battery (w/ battery ground connected. Is there a spec on the GP harness Voltage?


Edit my meter tested .1 ohm pressed together as a test.

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Discussion Starter · #17 · (Edited)
Alright so I reseated the GPCM and hooked all connections back up. Seems strange how it would be 2, and 6 the. 2, 4 and 6. Then the other mil codes

Per the DTR video above , he references 3 cycles of KOE On for the Mil to return. I shut the truck off 4 times and let it idle and the mil didn’t return.

We will see tomorrow if it comes back tomorrow when I start the truck to go to work. For the P067X codes


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Discussion Starter · #18 ·
Update … I suppose reseating the GPCM and the connections cleared the mil and it has *yet to come back.

I guess the problem was the gpcm all along as I can’t really find anything else wrong and everything ohm out in spec from the connectors to plugs.


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In one of DTR's videos, he pointed out the melted plastic in the harness connectors at the gpcm -- you have to pop the protective cover off to see this
 

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Discussion Starter · #20 ·
In one of DTR's videos, he pointed out the melted plastic in the harness connectors at the gpcm -- you have to pop the protective cover off to see this
Yeah I popped them off and there were no oxidation , separated pins now everything looked clean ish. I’ll have to pop em off at some point and see how they are

I came out of work , started the truck and no mil light or codes. So I guess it’s “ fixed “

Thanks for everyone’s input.


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