Folding the rear seat
The rear seatbacks can be folded to facilitate carrying long items or to increase the luggage capacity of the vehicle.
WARNING

To fold down the rear seatback:
1. Set the front seatback to the upright position and if necessary, slide the front seat forward.
2. Lower the rear head restraints to the lowest position by pushing and holding the release button (1) and pushing down on the head restraint (2).

3. Pull on the seatback folding lever (1) located in the trunk.

4. Fold the seatback toward the front of the vehicle.
5. To use the rear seat, lift and unfold the seatback to the upright position. Push the seatback firmly until it clicks into place. Make sure the seatback is locked in place.
When you return the seatback to its upright position, always be sure it has locked into position by pushing on the top of the seatback.
WARNING
When returning the rear seatback from a folded to an upright position, hold the seatback and return it slowly. Ensure that the seatback is completely locked into its upright position by pushing on the top of the seatback. In an accident or sudden stop, the unlocked seatback could allow cargo to move forward with great force and enter the passenger compartment, which could result in serious injury or death.
WARNING
Do not place objects in the rear seats, since they cannot be properly secured and may hit vehicle occupants in a collision causing serious injury or death.
WARNING
Make sure the engine is off, the shift lever is in P (Park), and the parking brake is securely applied whenever loading or unloading cargo. Failure to take these steps may allow the vehicle to move if the shift lever is inadvertently moved to another position.

The armrest is located in the center of the rear seat. Pull the armrest down by using the strap from the seatback to use it.
If your car is not equipped with a rear armrest, the rear cup holders are located at the back of the center console.
CAUTION
Seatback pocketHyundai Elantra AD (2016-2020) Service Manual: Specifications
Specification
ItemSpecificationPower source3VOperating temperature-30°C ~ +75°C (-22°F ~ +167°F)RF ModulationFSKLF ModulationASKRF frequency433.92 MHzButton number4FunctionDoor lockDoor unlockTailgate unlock
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Hyundai Elantra AD (2016-2020) Service Manual: Manifold Absolute Pressure Sensor (MAPS) Description and Operation
Description
Manifold Absolute Pressure Sensor (MAPS) is a speed-density
type sensor and is installed on the surge tank. It senses absolute
pressure of the surge tank and transfers the analog signal proportional
to the pressure to the ECM. By using this signal, the ECM calculates the
intak ...