A5 Moisture Sensor Glitch Triggers Engine Performance Drop

Had similar auto electronics problems on my 2019 A4 2.0 TFSI. The water sensor malfunction typically points to a faulty wiring harness connection near the intake manifold. The car sensor starts reporting incorrect readings when moisture gets into the connector housing. The rough running happens because the engine management system receives incorrect air-fuel mixture data. Last garage visit revealed corroded terminals within the connector block. A complete harness replacement was necessary as cleaning did not provide a permanent solution. The fix requires removing several components to access the wiring, including the intake manifold. This is a serious electrical fault that needs proper attention, temporary fixes like contact cleaner only mask the underlying issue. After replacing the complete harness assembly and connector, the car diagnostics showed all clear and the engine returned to smooth operation. The job takes about 4-5 hours for a qualified technician to complete properly. The issue tends to develop gradually over time as moisture slowly degrades the connections. Best to address it promptly when symptoms first appear.

Thanks for sharing your experience with the sensor issue. Just went through something very similar with my 2022 A5 a few months back. The moisture sensor fault definitely matches what I was seeing with the rough running and error codes. Really helpful to know about the wiring harness being the root cause. Could you let me know roughly how much the repair ended up costing you? Also curious if youve had any sensor faults pop up since getting the harness replaced? My local shop suggested a full replacement but I want to make sure its worth the investment.

Just got back from the garage where they resolved my sensor fault for good. The repair was much simpler and cheaper than expected, only 95 Euro to fix a damaged cable connection at the sensor plug. The malfunction indicator light hasnt returned since they repaired the faulty wiring. The auto electronics diagnostic revealed it was just a loose connection causing the moisture sensor malfunction rather than needing the complete harness replacement. The technician found corrosion in the plug housing but was able to clean and reseal it properly. Getting this fixed early likely prevented more extensive damage to the wiring system. The car sensor now reports correct readings and the engine runs perfectly smooth again. Quick tip for anyone facing similar issues, sometimes these electrical faults can be resolved with basic repairs if caught early enough. Glad I got it checked out promptly when the sensor testing first showed problems.

Finally got the issue sorted last week. Took it to a different mechanic who actually spent time testing the electrical system properly. Turns out the malfunction indicator was triggered by a corroded connector near the intake, just like you mentioned. The repair came to 280 Euro including parts and labor, more expensive than your fix but still better than a complete harness replacement. They cleaned up the connection points, replaced the damaged sensor and added some extra waterproofing to prevent future moisture issues. Been driving for about a week now and the engine runs perfectly smooth. No more check engine lights or rough idle. The car sensor readings are all normal according to my OBD scanner. Really glad I got a second opinion instead of rushing into replacing the entire wiring harness. Nice to resolve these electrical faults without major surgery on the car. Thanks again for helping point me in the right direction with the water sensor diagnosis.