Hi all I have been trying to test my glow plug circuit. I have checked all the plugs and they are fine, power to both number 3 plugs on the green and black connector but only have power to 9 on the black plug when I turn the key on. The truck has sat for days and it's around freezing out side. I think I might have. A short in the harness what do you guys think?

 

Have your ohmed all of the glow plugs from the gpcm plugs? Bad glow plugs will also show codes in the pcm. Get a Scan tool clear all codes and see what codes come up. If you turned the key on with some of the gpcm plugs disconnected there will be some glow plug codes so clear everything and retest. I take it the truck is not starting.

 

It looks like you have power where you're supposed to have it. Here are my notes (cut and past from a couple different threads).

6.0 Glow plug wisdom

Disconnect the four-wire connector to the passenger side glow plug harness (the one with the red lock tab). Using your ohm meter (and the appropriate scale if it doesn't have the auto-range feature), connect the black lead to the passenger side negative battery cable and the red lead to each of the four cavities on the glow plug harness end. You should obtain readings between 0.5 to 2.0 ohms on all four circuits (cylinders #1, #3, #5 and #7).
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Install an inductive ammeter on one bank at one of the two harnesses at the Glow Plug Controller Module (GPCM). You can get up to 200 A at first, but then should stabilize around 35-45 A. Check the other bank with the inductive ammeter. Both sides should read the same. If not, check the amps to each individual glow plug to determine which one (or ones) is bad. Each glow plug should draw 10-12 Amps.

Fuseable link for glow plugs about 4"" down the harness from where it connects to pass side battery. take the tape off. should be going under your a/c line.

All this information comes from the 2006 Service Manual.

Glow plug on time is dependent on oil temperature and altitude. The GPCM will
command the glow plugs on for 1 to 120 seconds. The GPCM does not operate
if the oil temperature is above 55C (131F)
It looks like the GPCM is really 2 units in one box.
Glow plug to ground 0.1~2 Ohms
Glow plug connector to GPCM connector Less that 5 Ohms

Pin #3 on both is the VBattery

Green connector
pin #1 is gp#5
pin #2 is gp#7
pin #6 is gp#1
pin #7 is gp#3
pin 8 goes to the PCM
pin 9 goes to the PCM

Black connector
pin #1 is gp#6
pin #2 is gp#8
pin #6 is gp#2
pin #7 is gp#4
pin 9 goes to the VPwr

The Glow Plug length of operation (up to 120 seconds) depends on oil temperature and the BARO reading. Glow plugs are not operated if the oil temperature is above 131 *F (55*C). The Glow Plug system is PCM controlled. The Wait-To-Start light is initiated by the PCM and is independent of the Glow Plug system. Above 131 *F, the PCM will still bulb-check the Wait-To_Start light. The GPM (GlowPlugMonitor) system (part of the OBDII system) is designed to monitor and detect failed glow plugs or failed wiring in the Glow Plug System.

https://www.ford-trucks.com/forums/1...ce-manual.html

 

I tested all the plugs and all read correct ohms at the green and black plugs. The truck is hard to start if it's not pluged in. As soon as it fires it runs fine. It was showing codes p0676 gp6, p0683,

 

Thanks for that I feel that the gpcm is bad. I think that I might get a new one. My thermostat was stuck open and the truck was only running around 110-114deg, I feel that May have something to do with the problem.

 

Yup. I don't have info on voltage readings for pins 8-9 an the green connector. I would suspect the GPCM but you could wring out the wiring from the connector to the PCM.

 

Great info rusty.Could have used this info on thursday night this week.I just replaced my gpcm yesterday.Seems common my truck is a 04 but only has 41,600k

 

I am searching the net on how to test the actual GPCM, can power be added to pin 9 (vpwr) or both #3 pins and jumped from one of the pcm pins (8,9) to activate voltage to the glow plug terminals 1,3,5,7 inside green and black on the bench? I see posts of guys guessing, or ruling it to be ohming out the harness and glow plugs, it would be nice to actually see one not having power and know for a fact that the GPCM is toast? bottom line, can this be tested on the bench using 12v to rule out bad or not, and if so..how? original poster Aaronlaron as a senior user posted "I feel that the GPCM is bad, may get a new one" pretty pricey for a guess, stealerships do that all the time, replace at our expense, as they`re not footing the bill

 

Do you have a digital clamp ammeter?

 

It should be under load if you are going to "bench test" it.

 

No..I read the post about checking amp draw while plugs are in, i want to test it on the bench connected to a battery, do not see how a ammeter clamp will do what I am asking. i had one, but a past friend decided he needed it more than I did

 

Now we are getting warm..what do you mean under load? I`ll power it up. jump it, whatever is required to see voltage going to the pins supplying the glow plugs, no one has said how to do it as of yet. Seen posts of 10.4 volts, etc...what i am asking is simple, just waiting for the right person to lay it out

 

Oh good, I’m getting warm. I don’t think I’m going to be the right person on this ......

 

It seems to me that jumping pins #3 to the PCM pins #8 & #9 would sent continuity to the glow plug pins, if one of 8 don`t have it, there we have our culprit.
Think I can do this without any harm as i am not putting power to it, just a guess
Seems rediculous to just guess its bad and spend a hundo just to be wrong.On a good/bad note, the unit i am dealing with is a dorman 904-282
which goes for about $90 vs. a motorcraft which is about $20 more

 

I think what the guys are getting at is that it’s not really useful to test the function of the GPCM by voltage alone. You may get a voltage reading on the output of an electronic module, but when you plug it into a load that voltage sinks to zero since there is not sufficient current flow. You may find that when the module is powered up you’ll get a residual output voltage even when the output is not “switched” on.