A4 Water Sensor Issue Causing Engine Performance Drop

I had a similar electrical fault with my 2004 A4 about 6 months ago. Having some experience with basic car maintenance, I initially thought I could diagnose it myself, but the sensor testing proved more complex than expected. The malfunction indicator kept lighting up intermittently, and the engine performance was inconsistent, especially after warming up. After checking various forum posts about auto electronics, I decided to have it professionally diagnosed. The workshop found that the main issue was a damaged cable connection to the sensor component. The wire insulation had worn through, causing intermittent electrical faults in the sensor system. The total repair cost was 95 Euro, which included testing the entire sensor circuit and replacing the damaged wiring harness section. The repair took about 2 hours, and the car has been running smoothly since. The rough running completely disappeared after the fix. To better assist with your specific case, could you share: Is your check engine light constant or intermittent? Does the rough running happen more in wet conditions? Have you noticed any correlation between weather conditions and the sensor malfunction? What diagnostic codes are you getting specifically?

Thanks for sharing your experience with the sensor issue. I had my last service at 42000 KM, and the problem started showing up recently at 44335 KM. While your repair seems straightforward, my diagnostic results show multiple electrical fault codes related to the sensor system. The check engine light stays on continuously in my case, unlike your intermittent issue. My engine also runs rough regardless of weather conditions, which suggests it might be more than just a wiring problem. The main error code I am getting is P0181, along with some secondary sensor fault indicators. Sounds like I might be dealing with a more complex sensor malfunction than a simple wiring issue. Has anyone dealt with multiple fault codes showing up together like this?

Thanks for providing those additional details about your sensor problems. Your description of the consistent check engine light and the P0181 code actually reminds me of what turned into a bigger repair job on my A4. While my initial problem seemed similar to yours, I eventually discovered the issue went beyond just the sensor wiring. The continuous check engine light and multiple fault codes pointed to a failed fuel temperature sensor unit, not just the wiring harness I mentioned before. The complete repair ended up involving: Replacement of the main temperature sensor unit, Testing of the entire sensor circuit, Recalibration of the new sensor system, Clearing all stored fault codes Total cost came to 320 Euro, significantly more than just the wiring fix. Labor took about 4 hours since they had to access and test multiple sensor components. Since then, my car has run perfectly with: No more rough running issues, Check engine light stays off, Fuel consumption back to normal, No moisture sensor related codes With your consistent check engine light and P0181 code, it sounds like you might be facing a similar sensor fault situation. Given the mileage you mentioned, a full sensor replacement might be the most reliable fix. Have you noticed any changes in fuel consumption along with the rough running?

Based on my specific situation with constant malfunction indicator issues and multiple sensor fault codes, I think I am indeed looking at a more serious repair than just wiring. The rough running combined with the P0181 code does suggest a failed sensor unit rather than just connection problems. My fuel consumption has increased by about 15% since these issues started. Given the car diagnostics results and symptoms described, it seems I should prepare for a complete sensor replacement and testing of the entire system. The 320 Euro cost reference point is helpful for budgeting, though I will need to confirm current pricing with a repair shop. The auto electronics in these models seem prone to sensor system issues around this mileage point. I will schedule a thorough diagnostic test to check if any other sensor components need attention while they are replacing the main unit. Better to address all potential sensor malfunctions at once rather than having to go back for additional repairs later. Would it make sense to also have them check the fuel temperature readings and other related sensors while they have everything opened up for repair?