Subaru 2013 BRZ - Manual (Page 218)

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2-4. Using other driving systems
BRZ_U
Disabling the TRAC system
If the vehicle gets stuck in mud, dirt or snow, the TRAC system may
reduce power from the engine to the wheels. Pressing to turn
the system off may make it easier for you to rock the vehicle in order
to free it.
In this case, the brake LSD function remains on.
To turn the TRAC system off,
quickly press and release the
button.
The Traction Control System OFF
indicator light will come on.
Press the button again to turn the
system back on.