VW Polo Moisture Sensor Causing Engine Troubles

The water sensor malfunction you describe matches what happened with my 2007 VW Golf TDI. The malfunction indicator light appeared along with rough running, especially during cold starts. Initial diagnosis pointed to a faulty moisture sensor, but the actual culprit was corroded electrical connections at the wiring harness. Auto electronics issues like this often mislead mechanics to replace sensors unnecessarily. The fix required cleaning the connector pins and replacing a section of damaged wiring near the sensor. The electrical fault was causing false readings, triggering the engine management system to run rich. This is a known weak point in several VW diesel models from that era. This type of problem typically starts small but can develop into a more serious issue if moisture continues to penetrate the electrical connections. Left unchecked, it can affect other sensors and cause additional malfunctions. Worth getting a second opinion from a workshop specializing in VW diesel electrical diagnostics. They should perform a complete circuit test rather than just replacing the sensor based on the error code.

Thanks for sharing your experience, it sounds very similar to my situation. I ended up having exactly the same car sensor problem with corroded wiring on my 2005 Polo TDI. The car diagnostics also initially pointed to a bad sensor, but the real issue was indeed the wiring. Would you mind sharing what you paid for the complete repair? Also curious if youve had any repeat electrical fault issues since getting it fixed? My Polo has been running fine for about 6 months now, but Im always a bit worried when it rains heavily.

Thanks for the follow-up. Glad to confirm your car sensor diagnosis matched my experience. Since seeing the mechanic last year, my moisture sensor issue has been completely resolved. The repair cost came to 95€ for fixing the faulty cable connections and cleaning the corroded plug components. After proper sensor testing and the wiring fix, I havent experienced any repeat electrical fault problems, even during heavy rainfall. The malfunction indicator hasnt reappeared, and the engine runs smoothly in all weather conditions. The key was addressing the root cause rather than just replacing parts. A thorough electrical diagnostics check showed the issue was indeed the wiring, not the sensor itself. For these VW models, keeping the connections dry and corrosion-free seems to prevent the problem from recurring.

My experience with the mechanic turned out pretty well this time. After getting your advice, I went to a VW specialist who actually took the time to properly diagnose the electrical fault. Just as you suggested, they found corroded wiring near the water sensor connection. The total repair came to 120€, which included a thorough electrical system check and fixing the damaged wiring harness. The moisture sensor itself was actually fine, it was just getting incorrect readings due to the bad connections. Its been running perfectly for the past 3 weeks, even through some heavy rain. The check engine light hasnt come back and the rough running is completely gone. Really glad I got a second opinion instead of just replacing parts based on the error code. Pretty sure this saved me from an unnecessary sensor replacement and potential future issues. The mechanic also applied some protective coating to prevent future corrosion, so hopefully this fix will last. Thanks again for steering me in the right direction with this sensor fault problem.