Wrong. Only the ICE is used for the ADUO ranking, but the whole PU can be changed:
https://www.formula1.com/en/latest/arti ... bKhHOd7GdD
Once ADUO comes into play, developments can be applied to a range of power unit components.
As per the FIA’s list, permitted upgrades include elements of the ICE, engine exhaust system, Turbocharger and waste gate/pop-off, ICE- or exhaust-mounted electrical components and sensors, ERS (and associated cooling systems), the MGU-K, and the car’s Control Electronics, along with hydraulic functions, fluids and ballast.
