Sitting in a reclined position when the vehicle is in motion can be dangerous. Even when buckled up, the protection of your restraint system (seat belts and air bags) is greatly reduced by reclining your seatback.
WARNING
NEVER ride with a reclined seatback when the vehicle is moving. Riding with a reclined seatback increases your chance of serious or fatal injuries in the event of a collision or sudden stop. Drivers and passengers should ALWAYS sit well back in their seats, properly belted, and with the seatbacks upright.
Seat belts must be snug against your hips and chest to work properly.
When the seatback is reclined, the shoulder belt cannot do its job because it will not be snug against your chest. Instead, it will be in front of you. During an accident, you could be thrown into the seat belt, causing neck or other injuries.
The more the seatback is reclined, the greater chance the passenger’s hips will slide under the lap belt or the passenger’s neck will strike the shoulder belt.

Seat cushion height (for driver’s seat)
To change the height of the seat cushion:

Lumber support (for driver’s seat, if equipped)
To adjust the lumber support:
1. Press the front portion of the switch to increase support, or the rear portion of the switch to decrease support.
2. Release the switch once it reaches the desired position.
Manual adjustment
Power adjustmentHyundai Tucson (LM) 2010-2015 Service Manual: Seat Belt Buckle Switch (BS) Description and Operation
Description
The SRSCM shall monitor the status of the driver and front
passenger seat belt buckle. The SRSCM provides one pin each for the
driver and front passenger seat belt buckle status input. The seat belt
buckle circuit operates from internal boost voltage supplied by the
SRSCM, and ...
Hyundai Tucson (LM) 2010-2015 Service Manual: ESC OFF Switch Repair procedures
Inspection
1.
Turn ignition switch OFF and disconnect the negative (-) battery cable.
2.
Remove the crash pad side switch assembly.
(Refer to Body - "Crash Pad")
3.
Check the continuity between the switch terminals as the ESC OFF switch is engaged. ...