Is it possible to remove O2 sensor without special Yamaha socket?

[fishcall]

if so, how?

[kingfish]

I did, with a combination of pliers, end wrenches and crescent wrench. See link below:

http://www.boatsetup.com/O2sensor.pdf

[kingfish]

do not use the heat to test please

you will ruin the o2 sensor

Yeah could be - I didn't test, I just replaced. They're pretty inexpensive.