Tire pressure warning comes on

It will go out on its own once the tires are filled

I found this on another site, it may help to understand what is happening, I also saw that there is a problem with the valve stems cracking since they're made out of aluminum and causing that problem. Here's the explanation provided on another site:

RodneyJ Answered 6 years ago
If a customer with a 2005 or later DaimlerChrysler vehicle equipped with Tire Pressure Monitoring (TPM) is concerned that the TPM lamp is on continuously, please be sure to inform the customer that the system is in place to warn of a low tire pressure situation, and a system diagnosis may not be required. The customer should be aware of the following: The Tire Pressure Monitoring (TPM) System will warn the driver of a low tire pressure based on the vehicle recommended cold placard pressure (the placard is located on the drivers side B-pillar).
The tire pressure will vary with temperature by about 6.9 kPa (1 psi) for every 6.5 Degrees C (12 Degrees F). This means that when the outside temperature decreases, the tire pressure will decrease - the customer should adjust his tire pressure for this decrease in pressure - please refer the customer to his vehicle owner's manual for information on how to properly inflate his vehicle's tires. The tire pressure will also increase as the vehicle is driven - this is normal and there should be no adjustment for this increased pressure.
The TPM System will warn the driver of a low tire pressure if the tire pressure falls below the low pressure warning threshold for any reason, including low temperature effects.
The TPM System will continue to warn the driver of low tire pressure as long as the condition exists, and will not turn off until the tire pressure is at or above recommended cold placard pressure. Once the low tire pressure warning has been illuminated, the tire pressure must be increased to the recommended cold placard pressure in order for the TPM warning lamp to be turned off. The system will automatically update and the TPM warning lamp will extinguish once the updated tire pressures have been received. The vehicle may need to be driven for up to 10 minutes above 25 kph (15 mph) to receive this information.


FOR EXAMPLE:

A 2006 300 has a recommended cold (parked for more than 3 hours) placard of 207 kPa (30 psi).

If the ambient temperature is 18 Degrees C (65 Degrees F) and the measured tire pressure is 186 kPa (27 psi) the TPM lamp will be OFF.

IF NOTHING IS DONE TO THE AIR PRESSURE IN THE TIRES and the ambient temperature drops to 20 Degrees F (-7 Degrees C) while the vehicle is parked, the approximate tire pressure will be 157 kPa (23 psi) and the TPM lamp will be ON.

IF THE VEHICLE IS DRIVEN TO REACH NORMAL OPERATING TEMPERATURE

WITHOUT ADJUSTING THE AIR PRESSURE and the ambient temperature stays at -7 Degrees C (20 Degrees F), the approximate tire pressure will rise to 186 kPa (27 psi) and the 1PM lamp will be ON.

To turn the TPM lamp OFF the tires must be inflated to the vehicle recommended cold placard pressure.

In order to properly maintain vehicle tire pressure, please refer to the owner's manual for additional information regarding tire inflation.

NOTE :Tire pressure should always be set based on cold inflation tire pressure (defined as the tire pressure after a vehicle has not been driven for more than 3 hours - and in outside ambient temperature).

Seasonal temperature changes will affect tire pressure, and the TPM system will monitor the actual tire pressure in the tire.
If a diagnosis of the system is required (for example, the lamp did not extinguish, or the lamp is flashing), please refer to service information available in TechCONNECT for additional information for TPM diagnosis. Please be aware that if the Wireless Control Module (WCM) is replaced, the TPM placard values may need to be reprogrammed. The TPM placard values do NOT need to be updated if the WCM has NOT been replaced, the TPM placard values are properly set at the factory.

By operating the tire pressure warning reset switch, the tire pressure warning ECU can be set to issue a warning at an inflation pressure that corresponds to the standard pressure of tires .Therefore, you must set the warning threshold to the proper value in order to comply with the local regulations .Operate the tire pressure warning reset switch only after the inflation pressures of all tires have been adjusted on the vehicle.To initialize the system, press and hold the tire pres- sure warning reset switch for 3 seconds or longer with the ignition switch in the ON position. When the system receives the
initialization signal, the warning light blinks 3 times (1 second on, 1 second off). During initialization, the tire pressure warning valve and transmitter measures the inflation pres sure of the tire, and registers the signals that are transmitted into the tire pressure warning ECU at a frequency of once per minute. The initialization process is completed when signals from all the tires have been received. It takes a few minutes .

Tire size Inflation Front Inflation Rear
P 195/65 R15 89S 30 psi 30 psi
195/65 R15 91H

P 205 /55 R16 89H 32 32 psi
P 215/45 R17 87W
205/55 R16 91V

Open the drivers door and look at the decal. If it is missing google the question you asked.

Step 1:

You could have a bad tpms sensor in one of the tires here's how to check it

Step 2:

Reading TPMS codes and clearing them
There is a simple procedure to perform a self diagnostic and clear the codes.

1) Turn IGN switch to ON.
2) Locate the TPMS warning check connector. It is a single loose wire with a connector located under the dash next to the steering column. It may be bundled with the OBDII diagnostic connector.
3) Using a suitable piece of bare wire inserted into the connector (a paperclip will do), momentarily ground the wire to the chassis.

NOTE: If you are uncomfortable doing this, then don't. You could damage your vehicle if the wrong wire is grounded.

Step 3:

4) The TPMS low tire pressure warning light will blink error codes as follows:

5sec. ON - 5sec. OFF
Long (1 sec) blink = First digit (2 blinks = 2)
Short (0.2 sec) blink = Second digit (ie 3 short blinks = 3)

There is a 2 second pause between multiple codes.The cycle will keep repeating starting with 5sec. ON

Codes:

15 - Front LH tire pressure drops to 26 psi or less.
16 - Front RH tire pressure drops to 26 psi or less.
17 - Rear RH tire pressure drops to 26 psi or less.
18 - Rear LH tire pressure drops to 26 psi or less.
21 - Data from front LH transmitter can not be receive.
22 - Data from front RH transmitter can not be receive.
23 - Data from Rear RH transmitter can not be receive.
24 - Data from Rear LH transmitter can not be receive.
31 - Checksum data from front LH transmitter is malfunctioning.
32 - Checksum data from front RH transmitter is malfunctioning.
33 - Checksum data from rear RH transmitter is malfunctioning.
34 - Checksum data from rear RH transmitter is malfunctioning.

5 short blinks - System is OK.

5) To clear the codes, turn the ignition OFF.

The LOW TIRE PRESSURE warning light will come on when the pressure is 25% below the manufacturer's recommended pressure. If I recall correctly, the 2007 Sonata has a manufacturer's recommended tire pressure of 30 psi. There is a tire label (sticker) on the inside driver's door jamb ('B' Pillar which tells you what the manufacturer's recommend tire inflation pressure should be. Once you have that value, you can calculate 25% of that & find the pressure at which the warning light should come on. NOTE: The TPMS (Tire Pressure Monitoring System) does not continually nor constantly scan the sensors in the wheels for this information - once every 3 to 10 minutes.

that is the low tire pressure warning. check and adjust all your tire pressures to the spec that is located on the door jam should be approx 33 psi 35 should work. in most cases this will fix your problem but you may have to drive it for a short while to wake sensors up after inflating to proper level.if you have a screw, nail...etc the light will come back on shortly. your tire pressures should be checked at least everytime you have your oil changed but in some cases where the ambient temp changes alot they need be checked more often.the only otherthing that would keep this light on is if a tire pressure sensor has been damaged, missing, battery dead in it or a malfunction in tpms syst. most cases adjusting you tire pressures will turn it off though.

Check all the tires with a pressure gauge and fill each tire to 33 PSI when cold (not right after driving). Also, if the light does not go off after you perform this procedure, then you will have to check and fill the spare tire to 33 psi to get the engine to shut off. Most Jeeps don't have a sensor on the spare, but I thought I would mention it.

it may be the tires warm up enuff to raise the air pressure to turn of the light.... check the pressure and set to about 30 psi

make sure all your tire pressures are above 35psi. the light will come on if your tires are below 28 psi. check all your tires for tire pressure. if pressures are low, add air and drive truck at 35+mph for about 1 mile and the light will go out unless you have a sensor problem, but fotha the light will be flashing. so to sum it up, check your tirpressures and make sure, that you have 35 psi in all 4 tires.