Audi S5 Knock Sensor Issues & Troubleshooting Guide

Having dealt with similar symptoms on my 2006 A5, I can share my experience. The engine knock and poor performance issues you describe match what I encountered. After the warning light came on, I noticed the same problems with rough idling and increased fuel usage. My issue turned out to be a loose wiring connection to the knock sensor. The connection had degraded over time, causing incorrect ignition timing and engine performance issues. The repair involved replacing the wiring harness and ensuring proper connection to the sensor. Total repair cost was 95 Euro, which covered both diagnosis and repair work. The fix resolved all symptoms completely, the engine knock disappeared, fuel economy returned to normal, and the warning light turned off. Before suggesting specific solutions, it would help to know: Has the check engine light code been read? Did these symptoms appear suddenly or gradually? Have you noticed any other electrical issues? When was your last routine maintenance performed? With my moderate experience working on these engines, I strongly recommend having a professional diagnose the exact issue, as similar symptoms can have multiple causes. A proper diagnosis will prevent replacing parts unnecessarily.

After reading the code with my scanner, it showed P0327, knock sensor circuit low input. Last service was done at 158531 KM with a full inspection. My malfunction indicator came on gradually over a few weeks. The engine knock gets worse when the engine is under load and poor performance is really noticeable on the highway. No other electrical issues noticed. The extra fuel consumption is hitting my wallet hard, burning about 25% more than usual. I had my mechanic check voltage at the sensor connector and it shows correct readings. So appears to be the sensor itself rather than wiring. Anyone know if this matches their experience with a bad knock sensor? The part cost seems reasonable but labor might be tricky given the location.

Based on the P0327 code and your symptoms, this definitely points to the knock sensor. When I had my A5 fixed, the initial voltage readings also looked normal, but the sensor itself was faulty. These sensors can degrade internally while still showing proper voltage. The extra fuel consumption matches exactly what I experienced, about 20-30% higher than normal because the engine management system defaults to a conservative timing map when it cant trust the knock sensor data. The engine knock under load is also typical, as the computer cant properly adjust timing. The repair was actually simpler than expected in my case. While access is tight, a competent mechanic can usually replace the sensor in about 2 hours. My total cost ended up being 280 Euro including the part and labor. Just make sure they check the mounting surface when installing the new sensor, any debris or uneven surface can cause the new knock sensor to malfunction. After my repair, the check engine light cleared, fuel economy went back to normal, and the engine knock completely disappeared. The fact your malfunction indicator came on gradually, like mine did, is another typical sign of a failing knock sensor rather than a wiring issue. Getting it fixed sooner rather than later is worth it just for the fuel savings alone.

Thanks for that detailed information about the knock sensor symptoms. The P0327 code really helps confirm what I was suspecting. Your experience with gradual warning light onset and sensor voltage readings matches my situation perfectly. I just scheduled the repair for next week. The parts cost came in at 180 Euro and labor estimate is 2 hours at their standard rate. A bit steep but still cheaper than continuing to burn extra fuel at these prices. The shop confirmed they will clean the mounting surface thoroughly during install. Will update once the repair is done, but feeling confident this will resolve the rough idle, engine knock and high fuel consumption issues. The fact that your symptoms cleared up completely after sensor replacement is really reassuring. Just hoping there are no surprises when they get in there, but the check engine code and symptoms seem pretty conclusive for knock sensor failure. Thanks again for sharing your detailed repair experience. It helped give me confidence to move forward with the fix rather than continuing to troubleshoot other possibilities.