Tiida Tailgate Sensor Fault

Sounds like a tailgate hall sensor fault. Those things are notorious. You checked the wiring, good, but did you look at the plug connection? Sometimes they corrode or loosen. If the connection is good, the sensor might be bad. You'll need a multimeter to check the voltage and signal. If you aren't familiar with electrical work, it might be best to leave it to a professional, you could make things worse.

When you say check the voltage and signal, what specific values should I look for? I have a multimeter, but I don't know the expected readings for a working hall sensor.

Providing specific voltage values is hard without the exact wiring diagram. Even with the diagram, poking around with a multimeter without experience can cause more issues. Given your description, the error code, and the symptoms, it points to the sensor or wiring. Honestly, to avoid frying something, I recommend taking it to a workshop.

Thanks for the advice. I'll schedule an appointment. The estimated repair cost is about 95€, which seems reasonable. I appreciate your time.