VW Up Sensor Fault Causing Poor Performance Issues

Having worked on cars as a hobby mechanic, I faced a similar issue with my 2014 VW Polo with the 1.0 TSI engine. The symptoms you describe match what I experienced, poor performance and increased fuel consumption. Initially, I also thought it was just a faulty temperature sensor, but when I took it to the workshop, they discovered a small leak in the exhaust system near the heat sensor connection. The exhaust component needed proper inspection, and they found that the sensor wasn't the main culprit. The complete fix included sealing the leak and replacing the exhaust sensor, totaling 265€. After the repair, fuel consumption returned to normal and performance improved significantly. To better assist you, could you share: Has your Up had any recent exhaust work done? Are you noticing any unusual exhaust sounds? Which engine variant do you have? Have you scanned for specific error codes? Getting these details would help determine if your issue matches what I experienced. The exhaust system is quite similar between the Up and Polo of that generation, so the repair process might be comparable. Consider getting a proper diagnostic scan, sensor replacement might not be the only fix needed, as my case proved.

Thanks for sharing your experience. Like my initial post mentioned, I have the check engine light issue in my Up with 17480km. Had the car serviced last month where they did a general inspection but clearly missed this developing problem. After reading your reply, I checked underneath and noticed a faint ticking sound near the exhaust sensor connection point, which I hadn't spotted before. Temperature fluctuations showing on the dash make more sense now, thinking it could be a similar exhaust component issue like you had. I have the 1.0 MPI engine and will get it properly diagnosed with a scanner tomorrow at a workshop. The emission control system issues you mentioned with your Polo sound very similar to what I am experiencing. Will update once I have the error codes and know more.

Thanks for the update about your Up. Those symptoms you mentioned, especially the ticking sound near the exhaust sensor, are really familiar to what I experienced with my Polo. The temperature fluctuation showing on your dash is particularly telling, as it matches the exhaust system behavior I saw before getting mine fixed. The 1.0 MPI engine in your Up uses a similar exhaust sensor setup to the TSI, and temperature fluctuations often indicate either a failing sensor or a small exhaust leak affecting the readings. Getting it scanned is definitely the right move, when I had mine diagnosed, error code P0128 showed up, pointing to the temperature sensor circuit. Since you mentioned a recent service, have them check the exhaust component connections too. In my case, the exhaust leak was small enough to be missed during regular inspection but significant enough to throw off the heat sensor readings. Let us know what the scanner shows. If it is similar to my situation, the fix should be straightforward, though costs can vary depending on whether you need just the sensor or additional exhaust system repairs.

I really appreciate all the detailed feedback. Got the car checked today and you were spot on, error code P0128 came up just like in your case. The workshop found a small crack in the exhaust near the heat sensor, which explained the ticking sound and temperature reading issues. The engine management system was reacting to incorrect readings from the exhaust sensor due to the leak. Total repair cost came to 290€ including a new sensor and welding the exhaust component. Already noticed better performance on the drive home and the engine light is finally off. Good thing I checked here first, might have wasted money just replacing the sensor when the real issue was the exhaust leak. Car runs like new now and fuel consumption is back to normal. Thanks for helping me identify the actual problem rather than just guessing at sensor replacement.