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Old 11-27-2010, 05:08 AM
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Glow Plug DTC keep coming back

My truck had set DTC's P0672 & P0678 indicating glow plug circuit failure on cylinders 2 & 8. As an inexpensive test, I bought a single new glow plug and put it in #2 hoping that one code would not return. Cleared codes, but on next cold restart, both codes came back. What's next, a new GPCM?

Also, on other threads there are a lot of ideas on pulling the glow plug harness out. I have a little craftsman right angle screwdriver for tight places

that I was able to hook into the slot where the super-expensive-for-what-it-is ford tool goes and pull the harness out. Just another idea . . .

Thanks,
Hemicbx
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Old 11-27-2010, 05:14 AM
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Since the glow plug that you changed showed up bad again I would say check the wireing from the glow plugs to the module if they check good then suspect the module.
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Old 11-27-2010, 10:04 AM
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I pulled the drivers side glow plug harness plug apart right above the valve cover, left them connected to the glow plugs. The wire colors on the harness are yellow, red, white, blue. i measured resistance from each wire's terminal to battery negative post. resistance was 0.6, 0.6, 0.8, 0.7, respectively. -'m not at the pc to be able to search right now, but I seem to recall that being the right range; at least they're consistent. Reconnected driver's seide harness to main harness.

Then I pulled the black and the green connectors from the GPCM. Values are as follows (all values without units are Ohms)

GPCM Pin #, Blk Connector, Grn connector
1, .8, .7
2, .6, .5
3, 12.5V, 12.5V
4,
5,
6, .7, .5
7, .7, .6
8, no terminal, Open
9, .931kOhm, .793kOhm


thoughts?

Hemicbx

Last edited by Hemicbx; 11-27-2010 at 10:48 AM.
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Old 11-29-2010, 01:10 PM
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Before I go out and drop $125+ on a module, I'd like to get a second opinion now that I have meaningful data. The way I see it, I'm in line with all the resistance checks outlined in the 6.0l Bible Hard Start Diagnosis tests


To me, that says module.

BTW, the truck does seem to start OK.

Thanks

Hemicbx
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Old 11-29-2010, 01:25 PM
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I have the GP #1 code, P0671 and P0600(i think) which is a serial communications link failure. I replaced the GPCM and same codes. I am assuming the problem is in the wiring, but haven't had a chance to chase it down. I have to plug the truck in below 55 degrees for trouble-free cold starting.

How are your cold starts with those codes?
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Old 11-29-2010, 02:22 PM
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My cold starts are not really bad at all. It's been low 40's here the last few days. It will fire right up, sometimes it will kinda sound like one hole's not firing for about 5 or 6 seconds, then it smooths out. I do not have a block heater.
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Old 11-29-2010, 05:35 PM
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just had a few of the same codes and replaced the gpcm and everything is back to normal.
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Old 12-19-2010, 12:01 PM
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OK, it's taken me quite a long time to get back to settle this issue.

As many others have said, I got a new GPCM and the codes are gone.

Hemicbx
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Old 02-11-2014, 09:23 AM
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I had a similar condition, my DTC kept throwing a P0678. I tested #2 pin Ohms to battery ground and only had 0.5 Ohms resistance. Bought a new GPCM and DTC is now gone.
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