The front seat can be adjusted by using the control switches located on the outside of the seat cushion. Before driving, adjust the seat to the proper position so that you can easily control the steering wheel, foot pedals and controls on the instrument panel.
WARNING
NEVER allow children in the vehicle unattended. Children might push the adjustment switch accidently and get caught in the seat mechanisms while the seat is moving.
NOTICE
To prevent damage to the seats:

Forward and rearward adjustment
To move the seat forward or rearward:
1. Push the control switch forward or rearward.
2. Release the switch once the seat reaches the desired position.

Seatback angle
To adjust the seatback:
1. Rotate the top of control switch forward or rearward.
2. Release the switch once the seatback reaches the desired position.
Reclining seatback
Sitting in a reclined position when the vehicle is in motion can be dangerous. Even when buckled up, the protections 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.
Driver 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 tilt (1, if equipped)
To change the angle of the front part of the seat cushion:
Push the front portion of the control switch up to raise or down to lower the front part of the seat cushion.
Release the switch once the seat reaches the desired position.
Seat cushion height (2, if equipped)
To change the height of the seat cushion:
Push the rear portion of the control switch up to raise or down to lower the height of the seat cushion.
Release the switch once the seat reaches the desired position.

Lumbar support (if equipped)
To adjust the lumbar support:
1. Press the front portion of the switch (1) to increase support or the rear portion of the switch (2) to decrease support.
2. Release the switch once it reaches the desired position.
Manual adjustment
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Description
Continuous Variable Valve Timing (CVVT) system advances or
retards the valve timing of the intake and exhaust valve in accordance
with the ECM control signal which is calculated by the engine speed and
load.
By controlling CVVT, the valve over-lap or under-lap occurs,
which m ...
Hyundai Elantra AD (2016-2020) Service Manual: Variable Charge Motion Actuator (VCMA) Description and Operation
Description
The Variable Charge Motion Actuator (VCMA) is installed on the inlet of the intake manifold.
It consists of a DC motor which actuates the VCM valve and a position sensor which detects the position of the VCM valve.
The VCM system tumbles air flow entering into combustion
chambe ...