C2 Oil Level Warning

Sounds like a potential wiring issue, but have you actually tested the sensor's resistance and voltage output? A visual inspection isn't enough. Also, what specific error code are you getting from the ECU? Knowing the code would help pinpoint the problem.

I haven't tested the sensor itself electrically yet, just the plug and wiring for obvious damage. I will check the resistance and voltage. As for the specific error code, I need to check the error memory again. Is there a specific range of resistance I should be looking for on the sensor?

Without knowing the exact Citroen spec for that specific sensor, it's tough to give you an exact resistance range. However, based on your description (error message, warning light), and the fact you've visually inspected the wiring, it's highly likely the sensor itself is faulty or the connector is corroded internally. At this point, and considering it's an oil level issue, I'd recommend taking it to a workshop to avoid any potential engine damage. Peace of mind is worth the cost.

I took it to a local garage. They confirmed it was a faulty connection as you suggested - they cleaned the plug and charged me 95€. All good now!