I have an 07 Santa Fe car. I have a problem with the fuel gauge needle on the dashboard. Last night, after driving the car, I was sitting idle and I notice the fuel gauge needle on the dashboard go down to empty then back up to half. As I started to drive home, I notice the needle go down then back to half again.

This morning, I turned on the car (cold start) and the needle was doing the same thing. The needle goes down to empty then up then down.... and the CHECK engine light came on.

What is faulty? Sensor or fuse? Perhaps something else?

 

If the circuit from the tank sending unit to the instrument cluster should open for some reason the gauge will respond accordingly.
The job now is to verify where the signal is getting lost. I doubt a fuse is involved, however, the sending unit has a wirewound coil and wiper that when worn it can lose contact and produce no signal at times. One way to confirm is to take readings right at the fuel tank where the unit plugs into wiring harness.

 

Does this happen while vehicle is only moving or does it also happen while standing still??
Don't know if taking reading while vehicle is static would reproduce the OP complaint??
But, do agree on taking reading at fuel tank ...

 

Good point !
I would hope bouncing the vehicle some to cause some sloshing in the tank might produce some helpful results.