2001 hyundai sonata fuel gauge reads wrong level

This is a very common occurrence, the fuel sending mechanism is inside the fuel tank, attached to an arm is a float (a device that will rise to the top of the fuel level). When parked at an upward or downhill angle, the fuel will collect to the opposite side of the tank (liquids will go to a natural level) and cause the float to move the lever. As the lever moves it rubs along a winding of wires creating a different resistance along the way. This changes the amount of current that will flow through the fuel gauge and change the level indication. When you are on level ground it will take a short period for the fuel gauge to return to the correct reading.

These are two different issues, cam sensor has noting to do with your fuel level unit.

Yes inside the fuel tank itself there is a gas leveling unit. That reads the level of gas inside the tank and send a certain amount of voltage from it to the gauge itself. If the tank were full of fuel the voltage sent is greater than if the tank were empty. You will have to remove the gas tank or I actually prefer removing the truck bed to access the top of the fuel tank. Hope this helps.

This sounds like the fuel level sensor in the gas tank is going bad, or there is a bad ground at the tank. A technician using a scan tool can monitor the actual fuel level data to verify.
Another possibility is a bad stepper motor in the instrument panel, each gauge had a stepper motor to drive the needle.

Turn the ignition on and off several times before inspecting the gas tank because a blown fuse is the usual cause for fuel gauge malfunctioning. If the gauge remains motionless, check your fuse box and determine the fuse's location using your service manual.
Replace the fuse if the link is broken or damaged. Then, inspect the gauge's wire connections for cleanliness and make sure the wires are connected.
Turn the ignition switch to the "off" position. Attach one end of a jumper cable to the fuel-gauge terminal behind the gauge itself. Attach the other end to the ignition terminal.
Replace the sender unit in the gas tank if the gauge reads full and your car does not have a full tank. Replace the fuel gauge if the needle remains inoperative.

I'm not sure I am understanding your question. The low Fuel indicator light comes on, depending on how sensitive it is set, when you have between 2 and 5 gallons of gas left in the tank. This also depends on how accurate your fuel level sending unit is reading the fuel level in the tank. The low fuel level light depends on the level of fuel in the tank itself but other than using that sensor it has nothing to do with the fuel gauge itself. The fuel gauge may or may not be accurately showing the fuel level.

Sounds like the fuel level sending unit has gone bad in the tank. Although gauges do fail, the more likely cause is tank level sensor.

In a case like this, the culpret is most likely the fuel level sending unit, which is located on the fuel pump in the fuel tank. In most vehicles, the pump and the sending unit all come in one assembly, which means in order to get a correct reading on the gauge, you'll need to replace the fuel pump. And actually, considering the fact that you have to drop the fuel tank and remove the pump anyway, it's just good measure to change them as a set.

I hope this helps! :)

The sending unit in your tank is going bad replace it.