While the answer should be simple it could be complicated. 2004 year model cars have a GEN 2/3 Nav System UNLESS its been upgraded. My 02 has a GEN 4 system. The easiest way to check which GENERATION of hardware you have is to eject the DVD from the system in the trunk.

The latest GPS NAV system software DVD is 15.1 but you need the correct DVD for the GENeration of NAV hardware.

My GEN 4 part number is PT219-GEN04-15
GEN 2/3 part number is PT219-GN23E-13

BUT it’s ALWAYS best to call the parts dept at your local Lexus dealer for the newest info.