One of the most common causes of P0016 in any vehicle is going to be wiring issues. You’ll want to inspect the wiring harness for visible damage. A lot of the harness leading to and from the Crank/Cam sensors is going to be exposed to hot exhaust and vibration. This is a great place to start diagnosing P0016 in your Opel Karl. It’s quick and easy to do this before moving on to the sensors themselves.
I'm chalking this up as another car we never got in the States because of strange circumstances. And today, Buick sells some interesting Opels-badged-as-Buicks like the Regal GS (an Insignia) and the Verano (sort of an Astra sedan). They feel relatively German, which is an unusual thing for any product sold at a GM dealership here. I'm still waiting for that Astra GTC, which is kind of the Calibra of today. Something tells me that badging a hatchback so sleek and aggressive as a Buick might not work, though.