i had the same issue. i googled for days and I tried everything from resyncing, to changing batteries and even praying to the porsche gods. nothing worked. the proper fix is to purchase a new key head with electronics ($200ish) then bring it to the dealer for programming ($100-150 depending on time dealer allocates for programming). Also, be careful when purchasing keys online/ebay because you need the white tag or else the dealer will not program it.
another option that I ended up going with was to purchase an aftermarket keyless entry system. I purchased a keyless entry/remote start system for $50ish.
Amazon.com: Avital 4103LXL Remote Start System with Two 4-Button Remote: Car Electronics
install was about 10 wires, even less for just a keyless entry. the alarm still activates/deactivates since it is triggered by the power door unlock/lock.
not only did i get a working keyless entry system, i also picked up a remote start for the cold Chicago winters
the only con I can think of is that i have a separate fob for the keyless entry. but i dont mind since that is how the rest of my vehicles are. and of course you need to either know how to install remote start systems or have it professionally installed.
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