on a Xenon the gpu fan always runs faster than the cpu fan, when the console gets hot the gpu fan is the only one that speeds up on a Xenon, if you want both fans to speed up and help cool it you can do this mod to make equal fan speed before you do the 12v mod.
This mod still allows you to adjust the fan speed in fsd for jtags, it just makes the cpu fan spin at whatever speed the gpu fan speed is.
I can't remember where I found this pic but I can verify that it works and credit goes to whoever found the mod.