Seat Mii Electric Rain Sensor Fault

I experienced a similar sensor fault with my Volvo a few years prior. Symptoms were identical: wipers going haywire, headlights switching on in broad daylight, and the speedometer illumination acting up. In my case, the rain sensor needed recalibration. Have you explored this avenue? An error code stored in the memory would strongly suggest a sensor malfunction. Have you checked the sensor itself for any physical damage or obstructions? The rain sensor typically works by projecting infrared light onto the windshield and measuring the amount of light reflected back. Water droplets interfere with this reflection, triggering the wipers. Any disruption to this process can cause a sensor fault.

Recalibration, eh? How involved is that? And physical damage – you mean like cracks in the windshield itself?

Recalibration typically requires specialized diagnostic equipment to communicate with the car's computer and reset the sensor's parameters. While seemingly straightforward, it is best left to trained technicians. Regarding physical damage: yes, cracks in the windshield directly over the sensor could certainly interfere. However, a more common issue is the degradation of the gel pad that interfaces the sensor with the glass. This pad ensures optimal light transmission. Bubbles, as you mentioned, or general clouding of the gel can scatter the infrared light and cause the sensor to misread the amount of moisture on the windshield. Given the symptoms you describe, and your suspicion of bubbles forming, it is highly probable that the malfunctioning sensor is the core issue. I would recommend a visit to a workshop; they can confirm the diagnosis and replace the gel pad or the entire sensor assembly if necessary. Better have it checked as a faulty rain sensor can also sometimes interfere with other systems due to shared electrical circuits.

Cheers for the help. Turns out the bubbles under the rain sensor gel pad were the culprit. Cost 62€ to sort at the garage.