When you select TERRAIN mode, by pressing the TERRAIN button , it helps the vehicle to maintain its best driving performance by controlling all wheels, engine, transmission and braking according to road conditions such as snow, mud, sand, etc. 

• MUD mode: MUD mode is used to ensure safe driving by appropriately distributing the vehicle’s traction forces when driving on muddy, unpaved or rough roads 
• SAND mode: SAND mode is used to ensure safe driving by appropriately distributing the vehicle’s traction forces when driving on sandy, graveled or unpaved off-roads 
• SNOW mode: SNOW mode is used to appropriately distribute the vehicle’s traction forces and prevent wheel slippage when driving on snowy or slippery road

When the TERRAIN mode is deactivated, a vibration may be felt as the traction forces on the front and rear wheels of the vehicle are released. This vibration is not a mechanical failure.