My Hyundai sonata is overheating what can be the problem is wasn't like this up til now.

SOURCE: 2000 Elantra Overheating

First when vehicle is cold like in the morning check and make sure that the vehicle has enough coolant/ antifreeze in radiator and reservoir. If coolant is need use a 50/50 mixture of water and antifreeze. You will need some time to do this let car run at idle until the temp guage is in the middle NOT+ normal operating temperature. At this point if the thermostat should be in the open position. Let vehicle run and check to make sure that radiator fan comes on. This should come on when guage is about midway/half way. If temperature rises above half going to h/hot and fan doesn't come on, you either have a BAD FAN BAD FAN SWITCH BAD FAN RELAY OR BLOWN FAN SWITCH FUSE. You will need to check all of the following I will help if its needed. If fan comes on and doesn't go off and vehicle continues to get hot even with fan running. Feel radiator hoses and see if the lower radiator hose is cool/cold. If it is you have thermostat that stuck closed. Replace thermostat and fix problem. If all the above is good and vehicle continues to over heat. THE BAD NEW IS THAT YOU MAY HAVE A BLOWN HEAD GASKET /CRACKED HEAD /BROKEN WATER JACKET. Basically you will need a HEAD JOB at least a head gasket. ONe tell tail sign of this is oil looking like milkshake/chocolate milk-a creamish while residue in oil or antifreeze. Contact if you need hel0p. Good Luck and thanks for using FIX YA

SOURCE: Why doesn't the heater blow hot air?

If your "Check Engine" or "Service Engine Soon" light is on, you need to have that checked out first.
If not, the next thing you should check is your engine coolant level. (Antifreeze) If the coolant level is low, the engine coolant does not circulate through the heater core and the the heater doesn't work. The coolant level could be low for a number of reasons including a leaky hose, water pump, or head gasket. In any case, if it is found to be low, you need to find out why.
If the coolant level is OK then the thermostat function needs to be checked to make sure that the engine is reaching operating temperature.
If all of the above checks out OK, then the heater control valve and/or the blend air door in the HVAC housing needs to be checked for proper operation. (NOTE: some cars are not equipped with a heater control valve)

SOURCE: Hyundai Sonata 2006 - Check Engine light came on.

"Fuel system too lean at idle". It's an air/fuel ratio that is not correct, possibly a vacuum leak somewhere. Or a leaky exhaust pipe. Could be related to intake manifold gasket. Somewhere, air is getting into the engine.

I suggest taking it back to the dealer under warranty. I think Hyundai is 10yr./100k for the original owner. 5yr./50k if not. Ask first if covered, and ask why not id not covered.

SOURCE: 03 hyundai sonata air bag light stays on

I read on another site to check the "yellow" connector under the passenger seat. Connector ncould be loose or wires that go in the connector may be loose.

SOURCE: My 2006 Hyundai Sonata check engine light went on

code P0441 IS Evaporative Emission Control System Incorrect Purge Flow

code P0171 IS P0171 System too Lean (Bank 1