Mini Countryman Diesel Water Sensor Issue

The symptoms you describe, including the check engine light, stored error, and rough engine running, do align with a potential water sensor malfunction in your Mini Countryman diesel. Given the mileage, it is plausible. Have you performed any sensor testing, and can you share the specific error code stored in the system's error memory? Furthermore, have you visually inspected the cable and plug connection of the component for any signs of damage or corrosion?

Sensor testing... that sounds complicated. How would I go about doing that myself? And the error code, I'd have to dig it out again but it mentioned something about 'implausible signal'. What does that even mean when talking about a car sensor?

An 'implausible signal' error code suggests the sensor's output is outside the expected range. While DIY sensor testing is possible using a multimeter to check voltage and resistance, it requires specific values and procedures for your Mini Countryman's moisture sensor. Given your description, the likely cause is indeed a defective cable or plug connection. Due to the electrical fault, I recommend you consult your local auto repair workshop for more detailed diagnostics and repairs.

Just wanted to give you an update! You were spot on, it was an electrical fault in the connector for the water sensor. The workshop found corrosion and replaced the connector. Cost me 95€, but the engine runs smoothly again, and that pesky light is finally gone! Thanks again for your help!