SQ8 NOx Sensor Issues Lead to Exhaust Problems

Having dealt with a similar NOx sensor issue on my 2019 Q7, I can share some relevant experience. After getting a check engine light and exhaust symptoms, it turned out to be a faulty wiring connection to the NOx sensor. The repair was straightforward at the workshop, they identified a damaged cable and connector assembly affecting the NOx sensor readings. Total cost was 95 Euro including diagnostic work and parts. The fix resolved both the exhaust issue and the check engine warning. Key things the workshop checked: Cable connections and plugs, Sensor signal readings, Full diagnostic scan, Proper catalytic converter function The pollution control system is quite sensitive, so damaged wiring can trigger these symptoms. Getting it fixed promptly helps avoid potential engine performance issues. To provide more specific guidance, could you share: Current mileage, Any recent repairs or maintenance, Specific error codes from diagnostics, Whether symptoms are constant or intermittent This will help determine if your case matches what I experienced with the wiring issue.

Based on my 15732 KM and latest service records, I found the issue was indeed similar to your experience. The workshop confirmed intermittent readings from the emission sensor were causing the check engine light. The air-fuel ratio was fluctuating due to incorrect NOx sensor data feeding into the pollution control system. After a full diagnostic scan, they discovered the wiring harness near the catalytic converter had minor damage causing signal interference. The exhaust system was thoroughly checked, but no actual leaks were found. Total repair came to 180 Euro including parts and labor. The check engine light has stayed off since the fix three weeks ago. My specific error code was P20EE which matches the NOx sensor circuit malfunction. Would be curious if others got the same code with similar symptoms.

Thanks for the follow-up details about your repair experience. The P20EE error code is indeed a classic indicator of NOx sensor circuit issues in diesel engine systems. Your case mirrors my Q7 situation closely, though my repair costs were lower since only the connector needed replacement rather than the full wiring harness. The intermittent readings you mentioned are particularly telling, this matches the diagnostic pattern I experienced where the air-fuel ratio would fluctuate unpredictably. My workshop also did a full exhaust system inspection before focusing on the wiring, as exhaust leaks can mimic NOx sensor failure symptoms. For others reading with similar issues, the key takeaway from both our cases is that wiring problems near the catalytic converter are a common failure point in the pollution control system. The relatively low mileage on your vehicle suggests this might be a vulnerable area worth checking during routine maintenance. Since your repair three weeks ago has resolved the issue, the workshop clearly pinpointed the root cause. The stable readings since then confirm the pollution control system is now operating as designed.

Thanks everyone for the detailed insights. After dealing with this issue, I wanted to add my final thoughts about the repair process: The workshop did great detective work tracing my issues to the NOx sensor wiring harness near the catalytic converter. The pollution control system is now working perfectly with the new wiring installed. Total cost was actually reasonable at 180 Euro considering the thorough diagnostic work and parts needed. In case this helps others, my full repair timeline was: Initial check engine light and exhaust symptoms, P20EE error code detected during diagnostic scan, Wiring harness damage found affecting emission sensor readings, Complete repair and system reset, No issues in 3 weeks of driving since Most importantly, proper diesel engine performance was restored once the exhaust system had accurate NOx sensor data again. Worth mentioning my vehicle only has 15732 KM, so these wiring issues can occur even with relatively low mileage. Looking to hear if any other owners have dealt with similar nitrogen oxide sensor problems, especially getting the P20EE code. The diagnosis and repair process would be helpful to compare.