A1 O2 Sensor Failure Causing High Fuel Consumption

Had the same symptoms on a 2018 A3 1.4L TFSI. The check engine light came on while experiencing high fuel consumption. The oxygen sensor was indeed failing, causing incorrect air-fuel ratio readings. The oxygen sensor malfunction made the engine run rich, meaning it was using excess fuel. When the automotive sensor sends wrong data, the engine control unit cant properly adjust the mixture. This typically happens around 100k km mark on these engines. Initial diagnosis showed a faulty connection, but deeper testing revealed the catalytic converter was also affected by the rich condition. The repair involved: Complete oxygen sensor replacement, Cleaning catalytic converter deposits, Recalibrating engine management system This was a serious issue requiring prompt attention since running rich can damage other components. The car returned to normal fuel economy after repairs. Getting a second opinion is smart since accurate diagnosis is crucial, these symptoms could indicate other issues if not properly diagnosed.

Thanks for sharing your A3 experience. Currently facing a similar situation with my A1s exhaust sensor. I like that you mention the catalytic converter too, gives me something else to check. Quick question, do you remember the repair costs? Just trying to budget this properly. Also curious if youve had any recurring issues with the O2 sensor or fuel consumption since the fix? Let me know as this helps with deciding whether to stick with my current mechanic or seek another opinion for a thorough diagnosis.

Glad I could help with my experience. Just had the A3 back from the mechanic last week actually. Turned out the O2 sensor issue was simpler than expected, just a bad cable connection that needed fixing. Total cost was 95 Euro, which was a relief since I was worried about a complete sensor replacement. The exhaust sensor and fuel consumption issues havent returned since the repair. The check engine light is completely gone and fuel economy is back to normal. My mechanic explained that faulty wiring often mimics a bad O2 sensor reading, which can trick diagnostics into showing more serious problems with the catalytic converter. The key was finding a shop that properly tested the connections before jumping to replace the automotive sensor entirely. Sometimes the simplest fix is the right one. Sounds like getting that second opinion might save you some money in your case too.

Just got back from the mechanic and wanted to update. After getting a second opinion, turned out my exhaust system needed attention beyond just the O2 sensor. The new shop did a thorough check and found loose connections plus some buildup in the exhaust that was causing the fuel efficiency issues. Total repair came to 220 Euro, more than your case but still way less than I feared. The check engine light is now off and fuel consumption has dropped back to normal levels. Really glad I asked around and got that second opinion instead of rushing into sensor replacement. The new mechanic also showed me what to watch for in case similar issues pop up again. After seeing the actual problem, definitely making this shop my regular go-to for future repairs.