S40 water sensor error

I have a similar Volvo S40, and I experienced comparable issues not long ago. The symptoms you described align with a potential problem in the water sensor circuit. Have you checked the cable and plug connections to the sensor itself? A defective connection there is often the culprit.

Thanks for the tip! When you say "checked", what exactly did you do? Did you just look at it, or did you test for voltage, shorts, etc.? I'm fairly handy with a multimeter, but I'm trying to avoid ripping the whole harness apart.

By "checked," I mean a thorough inspection, including verifying the integrity of the wiring harness. I used a multimeter to check for continuity and proper voltage at the sensor plug. While I located the issue, I'd suggest visiting a competent workshop with experience in auto electronics for a comprehensive diagnosis. It will save you time.

Thanks a bunch for the help! You were spot on about the wiring. Turns out the plug connection was corroded. Cleaned it up, and the light's gone! Error's cleared, and she's running smooth again. Cost me 95€ for the visit to the workshop and some contact cleaner. Cheers!