The troubleshooting guide says that you should not get battery voltage at pin 19 & 20. However, I believe this is incorrect. I was trying to solve the same code as you and went through probably a similar process. I DID receive battery voltage at pin 19 & 20. Eventually I exposed both sensors, swapped them, the code jumped to the other bank, and I bought a new sensor. 3000 km on the new sensor and all is well.
You can read through my thread here:
https://rennlist.com/forums/boxster-and-boxster-s-986-forum/1139864-p0340-camshaft-bank-1-what-could-go-wrong.html
I realise that the problem is not always due to a sensor failure, but the impression I got when I started looking into it was that it was never a sensor failure.
Threaded Mode
