No separate TÜV certificate or registration is generally required.
The fuel tank is designed as a direct replacement for the original factory-installed tank and does not constitute a structural modification to the vehicle.
The assessment is carried out in accordance with §19 StVZO as part of the regular vehicle inspection.
This approach is in line with the EU vehicle type-approval framework, where replacement parts are not subject to individual approval when they do not alter the approved vehicle design.
Reference:
Regulation (EU) 2018/858 — EU vehicle type-approval framework
https://eur-lex.europa.eu/eli/reg/2018/858/oj/eng