LS4 Question
 

In a (so far unsuccessful) attempt to replace the plug on cylinder 1, I had to unplug the sensor, or whatever it is, next to the plug wire.

What is this thing?

Are you referencing the coil packs?

Or a different sensor near the engine?

A different sensor ON the engine.

If it's the sensor right near the front exhaust manifold and plug #1 it should be the engine coolant temp sensor

If this also isn't correct, can you provide a picture of the sensor in question. Thanks!