Lexus GS 350 Owner's Manual page 232

230
4-5. Using the driving support systems
Turning the LKA system on
Press the "LKA" switch to activate
the system.
"LKA" indicator will come on.
Press the switch again to turn the LKA
system off.
The LKA system will revert to off each
time the engine switch is turned to
IGNITION ON mode.