Toyota 2009 FJ Cruiser Owner's Manual page 194

2-4. Using other driving systems
CAUTION
n To avoid an accident
Do not use the rear differential lock system except when wheel spinning
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occurs in a ditch or on a slippery or ragged surface. Large steering effort
and careful cornering control will be required.
Do not lock the rear differential until the wheels have stopped spinning.
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Otherwise, the vehicle may move in an unexpected direction when the dif-
ferential lock is engaged, resulting in an accident. This may also lead to
possible damage to rear differential lock component parts.
Do not drive over 5 mph (8 km/h) when the rear differential is locked.
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Do not keep driving with the RR DIFF LOCK switch on.
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