I have just joined this forum and I am very glad to have found such an in-depth resource from knowledgeable Hyundai owners.

I am a huge fan of the Hyundai's and just purchased my 3rd Sonata (2013 SE), a pre-owned model from Carmax.

I received 2 key fobs from Carmax. One of them works flawlessly, however the other one did not work at all.
When I went to start the car with the faulty fob, the display did not find the fob via the proximity locator and I had to insert the fob in the center console slot to start the vehicle. At this point, the red light did not illuminate on the faulty fob.

When, I replaced the fob battery, the red light DID illuminate, but the buttons on the fob still do not work to lock or unlock the doors. However, the proximity sensor did recognize that the fob was nearby enough to start the vehicle without my having to insert the fob into the center console slot.

I am completely stumped as to whether this is an issue with the fob being de-programmed or something else.

Please keep in mind that this issue is isolated to only inky fob, as the other one works just fine.

Any feedback would be greatly appreciated.