[jcm3]

I'd been getting a P0672 for a while (cylinder 2 glow plug circuit open), and at first when I'd clear the code it wouldn't come back for a few months. Then, it eventually started coming back right after I started it. At first I couldn't tell there was anything wrong, but it got to where it was getting harder to start unless it was very warm so I figured I better fix it before winter gets here.

I bought the glow plugs at the dealer, and almost talked myself out of the wiring harnesses. I'm glad I bought them. I even bought the little tool to remove the glow plug connectors, soaked each in WD-40, and was as careful as I could wiggling it out. On the driver's side, two of the four broke so I was glad I had the harness at the ready.

Funny thing, when I tested the 'bad' one with my voltmeter once I took it out, it was good. Don't skimp on the harness.

Pretty easy job, it would have probably taken me about an hour or so taking my time, but I decided to use my pressure washer and clean off the crud while I had the fender liner out. What a difference. I had a bit of crud in a few areas that I couldn't see with the fender liner in there, so it's nice and clean now. I cleared the codes and took it for a spin, and no more check engine light, so fingers crossed.

 

[jcm3]

Took her for a spin this morning and the check engine light came back on. I checked the codes when I got back, and found cylinders 3 and 5 showing codes for glow plugs, so I'll swap out the passenger side glow plugs and harness also (already have the parts).

But, I'm showing a cylinder 2 error again, after replacing the glow plugs and wiring harness on the driver's side. Ugh. Any idea what else would contribute to the error after replacing the glow plugs and harness? I read something about a glow plug control module, and will have to do more research on that.

 

[ZMANN]

I did the pass side last month the GP's and harness were easy the fender liner wasn't lol
you can test all the components before replacement but I would bet your GPCM is acting up

what year is your truck ? probably a later model the early ones did not throw a cel for a GP issue

 

[jcm3]

I did the pass side last month the GP's and harness were easy the fender liner wasn't lol
you can test all the components before replacement but I would bet your GPCM is acting up

what year is your truck ? probably a later model the early ones did not throw a cel for a GP issue

Mine is a 2005, and I agree, the fender liner is probably the hardest part of the job.

I need to pick up a GPCM online and swap that bad boy out.

 

[Hydro]

Usually the connector terminals in the GPCM harness are the weak point
Green for 1357 -- Black for 2468

 

[6riders]

Mine is a 2005, and I agree, the fender liner is probably the hardest part of the job.

I need to pick up a GPCM online and swap that bad boy out.

Check the plugs at the gpcm. There is a rubber seal that will come out of place and keep the plug from fully engaging.
I had the same problem as you and when inspecting the plugs, I saw the seal had "pushed" into the plug. Once I got that sorted, plugged everything back in and cleared codes, the codes never came back. Pretty easy to inspect and a free fix, if this is your problem.

 

[jcm3]

Check the plugs at the gpcm. There is a rubber seal that will come out of place and keep the plug from fully engaging.
I had the same problem as you and when inspecting the plugs, I saw the seal had "pushed" into the plug. Once I got that sorted, plugged everything back in and cleared codes, the codes never came back. Pretty easy to inspect and a free fix, if this is your problem.

Awesome, I will pull them out, inspect them, put some dielectric grease on them and see what happens!

Edit: I just checked the plugs at the GPCM. I noticed that there is a button you have to depress at the bottom of the connector to pull them out, but they both came out without pushing anything and there isn't any kind of a click when I push them in. My guess is that during some work prior to my owning the truck, they were just pulled out and the plugs broken. Ugh. I really don't want to trace and replace those harnesses, I assume they're the wiring harnesses that go from the end of the glow plug harness to the GPCM.

I pulled them out, put some dielectric grease on them and pushed them in. It seemed to start fine (during the glow plug issue, the truck struggles to start, cranks slower and you can tell something isn't right), so I may have a better connection now. I'm going to see if there's a way I can keep them in using a zip tie or some other method before considering the work needed to replace the ends of the wiring harnesses that plug into the GPCM.

Thanks for your tip.

Edit: Edit: I just started it after clearing the codes and the check engine light came right on, so the GPCM is bad also. I ordered a new one earlier this morning, so I'll swap it out anyway.

 

[jcm3]

Replaced the GPCM, the bad news was I still had a check engine light. The good news was it was only showing glow plugs 3 and 5, not 2 (like I was getting a code for after the GPCM swap.

I replaced the odd glow plugs and wiring harness today, and all good. No codes, and it starts like it should.

 

[jcm3]

Here's a little chronology of this, in case it helps anyone in the future.

I started getting a check engine light about a year and a half ago or more, for the cylinder #2 glow plug. I was just clearing the code, and it would come back in about six months or so. Eventually it got to where it would come back instantly, but no change in starting behavior so I just ignored it (for too long). Eventually it started really struggling to start, and I knew I needed to fix it.

I ordered all eight OEM glow plugs and the two wiring harnesses.

I first changed the even side (since I was getting a code for cylinder Number 2), and took it for a test drive. I checked the ones I took out, and the cylinder 2 glow plug tested good. Still got a code, but for cylinders 2, 3 and 5. I already changed cylinder 2, and the wiring harness, and checked it with a volt mater, so I assumed at that point the GPCM was bad.

Replaced the GPCM with an OEM one, took it for a test drive, and got a code again, but just for cylinders 3 and 5. So, I knew I had to finish the job. I took care of the passenger side today, took it for a test drive, and all good. Starts like it should and no codes.

A few comments:

• I bought the $15 tool to pull the glow plug wiring harness, and although some may get lucky, even with soaking the plugs in WD-40, two still broke. I'd skip the tool, and make sure you have the wiring harnesses or you could get stranded. For the passenger side, I didn't worry about it and just yanked them out.
• The GPCM must have been the first thing to go bad, because the #2 glow plug was never probably never bad.
• If you start having starting problems (it was cranking slow, and if it got cool at all would take a while to start, almost sounding like it was flooded), could be a glow plug or the GPCM.

All in all, easy job, and probably about $250 for the 8 glow plugs, two wiring harnesses and the GPCM.

Pretty easy job, pulling the fender liners is probably the most time consuming part of the job. The first side took longer because I took my pressure washer to the engine compartment while I had the fender liner out, but if you just do it and don't spend time cleaning, it is probably about an hour per side. Maybe a little bit more the first time and less the second time.