Arducopter autotune fails

No, the pixhawk is not defective. But you do need to follow some instructions in order to get it working.

First update to ArduCopter 4.5.1 firmware version. Then install https://github.com/ArduPilot/MethodicConfigurator/actions/runs/8603225557/artifacts/1394874278 and follow How to methodically tune (almost) any multicopter using ArduCopter 4.4.x