RS4 Moisture Sensor Issues Causing Engine Roughness

Had a similar electrical fault with my 2016 S4 last month. The engine also ran rough and showed a malfunction indicator for the moisture sensor. Initial diagnosis matched your error code. The actual problem turned out to be corroded wiring connectors leading to the sensor, not the sensor itself. This created a false reading and triggered the check engine light. The sensor testing revealed it was functioning correctly, but the connection was compromised. The repair involved cleaning the connector housing and replacing the damaged section of the wiring harness. The car sensor needed proper reseating with dielectric grease to prevent future moisture intrusion. A sensor fault like this can mimic more serious engine problems, but the fix was straightforward. If your symptoms match (rough idle, inconsistent sensor readings), focusing on the wiring connections first makes sense. This is a known weak point in these engines, especially as they age. Getting a second opinion from a shop that specializes in VAG electrical diagnostics would be worthwhile. The repair resolved all symptoms and the engine has run perfectly since. Not a major mechanical issue, but one that requires proper diagnosis and repair to prevent long-term problems.

Thanks for the detailed info about the sensor issue. Relieved to hear it was just the wiring connections, that matches what Im experiencing with my RS4. Car diagnostics showed similar symptoms on my end with the rough running and water sensor warnings. Been dealing with this for about 2 weeks now and looking to get it fixed. Would you remember roughly how much the repair cost you? Also curious if youve had any other auto electronics problems pop up since the fix? Want to make sure I budget correctly and understand if this might be part of a bigger electrical issue.

The repair cost came to 95 Euro for fixing the faulty cable connection to the water sensor. After seeing my mechanic last week, the issue was completely resolved. The auto electronics are now working perfectly with no sensor fault codes showing up. Like your RS4, my car had issues with rough running and incorrect sensor readings. The electrical fault was traced to a damaged connector, which is a fairly common problem. The sensor testing confirmed the actual sensor was fine, it just needed proper reconnection and waterproofing. Since the repair, all systems are functioning normally with no new warning lights or sensor malfunctions. The engine runs smoothly and the diagnostic readings are stable. This type of repair typically solves the problem completely without indicating wider electrical issues, provided the work is done properly. Looking back, getting it fixed promptly was the right call to prevent any potential cascade of sensor-related problems. The repair cost was reasonable considering the diagnostic work needed to pinpoint the exact connection issue.

Thanks all for the advice! Finally got my RS4 sorted at a different mechanic who actually knew what he was talking about. The malfunction indicator was spot on about the moisture sensor wiring being the culprit. Total bill came to 120 Euro which included a full sensor testing sequence and replacing the corroded wiring near the water sensor. The mechanic showed me the old connector, it was pretty badly corroded and definitely causing the sensor fault readings. Car has been running great for the past week with no check engine lights or rough running. The new mechanic also applied some special sealant around the sensor connection to prevent future moisture issues. Really glad I got a second opinion instead of paying for unnecessary repairs at the first shop. Definitely keeping this mechanic for future work. He took the time to explain everything and show me the actual problem rather than trying to upsell me on extra repairs. Sometimes paying a bit more for someone who knows what theyre doing saves money in the long run.