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Hey All! haven't been on here much but I'm always lurking!
Just happened to check codes today for fun and found something interesting. I've known about 2 or 3 glow plug codes since last winter but I looked today and I have a code for every single circuit. Thought that was kind of odd.... I already have 8 brand new plugs and both harnesses from Autonation sitting in the back seat, was just waiting till the fall to change them out. At 176k on the originals I decided to change them all. But now I'm thinking the GPCM may be faulty as well. Wanted to see your thoughts Thx!
I had a similar issue not to long ago. At first I had four glow plug codes then I got all eight. I thought that maybe the module next to the Passenger side Battery but before doing any tests I decided on getting new batteries (just for the heck of it) and when I was installing the new batteries I noticed that a connection was loose on the positive cable going to the battery. I think this is to power the glow plugs (i could be wrong). I tightened it and cleared the codes and have not had any error codes for the last 2-3 months.
Diesel tech Ron has a couple nice videos on simple testing of glow plugs. He walks thru unplugging the harness and uses either a test light or DMM to look for resistance in the circuit. Super easy and free to verify if the glow plugs are in spec.
We had three codes, and in testing discovered 2 of the gps were shot, but not the 3rd. Found a used GPCM, installed it and no more codes.
Also discovered the the harnesses can be very tricky to source the correct length.
I just replaced the GPCM the other day for a #2 plug code that would not go away
even with a new plug and good harness. The new module solved the issue.
Thanks for the replies! I have a feeling with me showing all 8 I either have a wiring problem somewhere or bad gpcm. I'll test each plug though just for the heck of it, love diesel tech Rons videos. Hope the harnesses I got are the right ones, went by the VIN....
I put two fresh batteries in the truck around Feb this year, but I'll double check the connections good thought Ruben!
I still need to get that IDS Sean. To many things always going on...
Oh man I am tired from drilling, chiseling and stoking the smoker
with charcoal. Got to love the taste of a good smoked bork butt.
I used mesquite charcoal and not the briquette kind and tossed in
some wood chunks for even more smoke. It was so good I can't work
on the truck anymore tonight of I'll pop.
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
Little update I tested all the plugs last night at the glow plug harness plug. Not the connector at the GPCM. Got the following results
Drivers Side: Yellow wire - 2.0 ohms Red wire - O.L.
White wire - O.L. Blue wire - .8 ohms
Pass Side:
Yellow wire - O.L.
Red wire - 7.7 ohms
White wire - 23.5 ohms
Blue wire - O.L.
O.L. Means no connectivity or a break in the circuit. So I'm guessing that means those are toast along with the others that have a higher resistance?
The readings obtained that are highlighted in bold, are the readings that are within range. The rest of the six readings are outside of the acceptable range.
So I replaced all 8 plugs and both harnesses over the weekend. I must say that was not as hard of a job as I was expecting. I removed the fender liners, and that made it much easier. Going from the top just seemed like a pain in my back, literally! I only had two of the eight harness plugs break. The rest popped out with ease.
So after the fact the truck starts instantly when cold, it was 37° or cooler the other morning. I cleared the codes, but two have popped back up.
Interesting that the two not working are the ones that were is spec before being replaced. Guessing here but I bet those two were still in spec because they were not getting energized for awhile and didn’t have a chance to burn out.
We had a similar issue, replaced the glow plugs, still had a code. New gpcm fixed it.
I'm not convinced I was getting accurate readings before honestly. Not sure how. But I tested each plug that I removed and all but one read O.L. whereas before 4 were giving me some type of reading when read at the connector prior to removal.
I suspect maybe the harness but can't be sure. I'm going to ohm them all again just to verify and see whats up. If the code persists I guess I'll try the GPCM. I know all the plugs I put in were good, tested each one.
There may be hope for my GPCM after all!
