Assuming you've checked the fuses, your best bet is going to be connecting a laptop with Forscan to check fault codes.
A cheap ELM327 with MS-CAN switch ($20 on Amazon) usually works, but the proper OBDLink EX ($60) is more reliable and gives you more abilities in the future (most of which you probably won't ever use, but it's nice to have the option).
If I had to guess, a sensor went out and the parking module is going into a fault mode, greying out the option.
A cheap ELM327 with MS-CAN switch ($20 on Amazon) usually works, but the proper OBDLink EX ($60) is more reliable and gives you more abilities in the future (most of which you probably won't ever use, but it's nice to have the option).
If I had to guess, a sensor went out and the parking module is going into a fault mode, greying out the option.