Failing O2 Sensor Draining A5's Fuel Economy

As someone with some experience working on Audis, I had a similar issue with my A4 2.0T from 2015. The check engine light came on and sensor testing revealed problems with the oxygen sensor heater circuit. The exhaust system really needs properly functioning O2 sensors to maintain optimal air-fuel mixture. When I brought it to my regular workshop, they found a faulty sensor connection, specifically a damaged wire and loose plug going to the O2 sensor. The repair cost me 95 Euro including diagnostics and labor. They had it fixed within about 2 hours. Not addressing this issue could lead to: Continued poor fuel economy, Higher vehicle emissions, Potential catalytic converter damage, Failed emissions tests To help provide more specific advice for your case, could you share: What year is your A5? Which engine variant do you have? How many miles/kilometers on the odometer? Are you noticing any other symptoms besides the increased fuel consumption? These sensor issues are fairly common on these engines, but the exact fix can vary depending on the specific model and condition.

Thanks for the helpful information about oxygen sensor issues. After my last service at 86706 KM, everything was running fine until this check engine light appeared. Just wanted to clarify that in my case, the car components showing the fault code specifically point to the post-cat sensor heater element, not a wiring issue. Getting a second opinion on whether the entire sensor needs replacement or if there might be a simpler fix seems sensible based on your experience.

Thanks for clarifying about the post-cat sensor heater element fault. When I had my oxygen sensor problem, I initially thought it was just a wiring issue too, but after further diagnosis, it turned out the sensor itself needed replacement. The malfunction indicator light in these cases usually points to a genuine sensor problem rather than just connections. Since you mentioned it started after the 86000km service, and the fault code specifically indicates the post-cat sensor heater element, replacing the entire sensor would be the most reliable fix. On my A4, I first tried cleaning the sensor connections, but the check engine light persisted. The complete sensor replacement cost me 285 Euro including labor. While more expensive than just fixing wiring, it solved the problem completely and improved my fuel consumption back to normal levels. The faulty sensor symptoms matched yours exactly, increased fuel consumption and the engine light warning. Since the post-cat sensor helps monitor the catalytic converter efficiency, getting it fixed soon would be wise to prevent potential exhaust system complications. Based on the mileage you mentioned, this type of oxygen sensor failure is fairly typical. These sensors usually need replacement every 60000-100000km depending on driving conditions.

I appreciate the detailed response and sharing your similar experience. Your suggestion about getting the post-cat sensor replaced makes a lot of sense given the symptoms and fault code. The cost estimate of 285 Euro for a complete sensor replacement seems reasonable, and knowing it solved similar issues with fuel consumption is reassuring. Since my car is within the typical replacement window for oxygen sensors based on mileage, I will go ahead and schedule the repair to prevent any potential damage to other car components. The check engine light and increased fuel costs are already concerning enough, but I definitely want to avoid any catalytic converter issues down the line. I will have my regular workshop handle the sensor replacement since they are familiar with the vehicle emissions system on these engines. Thanks for confirming that this is a fairly standard repair job that should resolve both the error code and fuel efficiency problems. This has helped give me confidence in moving forward with the fix.