Colin,
I had a similar problem with my 2007 LBZ 6.6L, one glow plug became faulty and triggered the check engine light with an error code. Happened late summer/early fall about 3 years ago. I went ahead and replaced the one that went bad, had no issues. It shouldn't harm anything. Probably more help than harm. My mechanic friend recommended replacing all of them eventually within a few months, so I did before winter, within 3 months of the first one going bad. Used all stock AC Delco glow plugs.

Rob

 

Replacing glow plugs is one of the easier maint items to DIY. After you remove the fender liner to get to the glow plugs, at least replace the four on that side. And make sure you have extra nylon rivets, as at least one will break when you remove them.
And my experience has been that if one glow plug fails, others will soon follow.
Just replace them all and be done with it
But yes, you can just replace one, but why?

2007 2500HD Classic 4x4 LBZ

 

Colin, ensure you start soaking them a good penetrating oil and let it soak. I then cranked my truck and let it get warm. Then I removed and replaced the glow plugs. Don’t forget to use some anti seize on them when installing.

 

Very good recomendations! THANKS!

 

I have had two high mileage trucks. The 2010 was over 853k miles when I sold it and the 2013 I have now with almost 680k. Might have one or two glow plugs go bad a year. Some of the plugs are still the original in that amount of miles.

 

I think I have replaced all my Glow plugs in 4 years. Right before winter I get 2 plugs that go bad within weeks of each other. just replaced #6 1 month ago it was #4 last year 2as #8 and #7. I have been tempted to to Velcro the inner liners in. LOL

 

Replace them as they go. No sense replacing glow plugs that work. I just keep a spare on the shelf.

 

When I got the code for glow plug #4 I bought 8 replacements. After I replaced #4, I drove for over 1.5 years before I got the code for #1. I just replaced it a couple weeks ago. Still have the other 6 glow plugs on standby in the garage.

 

My 15 yo LBZ threw it's first glowplug failure code last winter so I had it replaced.
No codes or problems since. I don't see the need or reason to replace the good ones that remain.

 

Most us don't see the need until we get tired of pulling off the wheel well liners to replace the next one But hey, maybe you are lucky....
I think the glow plugs on my LBZ lasted 12 years until the first one went.

2007 2500HD Classic 4x4 LBZ

 

My first one to go I just replaced it. A few weeks later another one quit. I bought a set of 8 and replaced them all and kept the good old ones and have been using them as replacements. It's about time for another full set after 310,000.

 

I replaced all of mine last year, after #3 threw a code, with around 148K. Was pretty easy to do. As several have mentioned above, make sure you soak the threaded area with penetrating fluid. I pulled my wheel liners when I got home and sprayed the glow plugs, and let them soak overnight, then sprayed them again in the morning. After lunch I started to replace them, and was done about an hour and half later. Just took my time, and yes I did apply anti-seize on the new threads, and torqued to specifications. Doesn't take much torque, so be careful. But to answer your original question: Yes, you can change just the bad one, but why not do them all.

 

I got a CEL, code said #2 glowplug was bad, got tired of seeing the CEL after about 5 months so I bought a new set of 8 Bosch plugs. When I pulled the fender liner out, I decided to check the resistance before I pulled it. Ohmed out to be the same value as the new one, so I cleaned up the connector-it had some oxidation on it-cleared the code and problem was fixed. Decided to repick the injector contacts while I had the liner out. Check your old glowplug before you pull it, #2 seems to get oxidized more than the others.