I have a note that the dealer replaced GP#1 @ 37,000. Now at 62,000 I got a code 1261. After verifying the harness was on correctly I proceeded to replace #1 on my own. Yes, it is possible without removing components, but it's tight; very tight. First off, it's easier to find the G-spot than GP#1, but it's there just behind the alternator.
Then you have to get the cap off. You can use Miller Tools 9286 Glow Plug Pliers for $149
Or you can use this:
An ordinary garden weeder for $1.50.
You will need a DEEP 10mm SOCKET. I also used a 10" wobble head extwnsion
I used clamps to keep the wiring harnesses out of the way.
Here's what my old one looked like:
Not bad, just dead. Theories on why number 1 only?
I used the old one to do a dress rehearsal for putting the rather fragile new one back in. Good thing too. As I tilted the socket toward the hole, the glow plug fell out and down into the engine compartment. I used a small piece of tape to wedge the gp into the socket.
Then, using the weeder, I manipulated the cap back into position. Good as new (which is still not that good, but acceptable.