VW Sharan Exhaust Leak Causes Power Loss & Rough Idle

Had almost the same problem on my 2012 VW Touran 2.0 TSI last summer. As someone with moderate experience working on cars, I first suspected the catalytic converter, but it turned out to be a faulty oxygen sensor (also called Lambda sensor). The symptoms were identical, rough engine running, check engine light, power loss when warm, and that distinct exhaust smell. The workshop diagnosed it using their diagnostic tool and found the rear oxygen sensor was giving incorrect readings, causing the engine to run rich. Total repair cost was 375€, including parts and labor. The mechanic explained that a bad oxygen sensor affects the fuel mixture, which explains the poor performance and smell. After replacement, the engine ran smooth again and fuel economy improved noticeably. For your Sharan, would be helpful to know: Have you had any diagnostic codes read? Does the exhaust smell like raw fuel? Did you notice any changes in fuel consumption? Are there any unusual noises from the exhaust system? Once you share these details, I can provide more specific advice based on my experience with the VW TSI engine.

Thanks for the detailed response. Yes, my Sharan with 124765km is showing similar symptoms, particularly the fuel smell and rough running. Checked the codes yesterday, showing P0420 catalyst system efficiency below threshold and P0135 O2 sensor circuit. Fuel consumption has gone up about 15% in the last month. The exhaust definitely smells like unburned fuel, especially at idle. There is also a rattling sound from underneath when accelerating hard. Given the age of the catalytic converter and these readings, I am wondering if both the cat and sensors need replacement. Has anyone tackled this specific repair and knows the parts and labor costs involved?

Thanks for providing those details. When my Touran had similar issues, the P0135 code also appeared alongside catalyst efficiency warnings. The rattling sound you mentioned is particularly concerning, I had the same noise and it indeed pointed to internal damage in the catalytic converter. In my case, after further inspection, both the oxygen sensor and catalytic converter needed replacement. The oxygen sensor malfunction had caused excess fuel to damage the catalyst over time. NOx sensors were also showing irregular readings due to the rich fuel mixture. The complete repair included: New catalytic converter: 850€, Front oxygen sensor: 220€, Labor costs: 400€ Total came to roughly 1470€, but it completely resolved the issues. The exhaust smell disappeared, fuel consumption returned to normal, and the engine ran smoothly again. Important to note that postponing the repair could lead to more extensive damage. Since your Sharan shows identical symptoms and codes to what I experienced, I would strongly recommend getting both components replaced. The rattling sound during acceleration typically indicates the catalyst honeycomb structure is breaking down, which can lead to complete exhaust system blockage if left unaddressed.

Thanks for the helpful input. After reading through the responses, I have decided to go ahead with replacing both the oxygen sensor and catalytic converter. The matching diagnostic codes and similar symptoms, especially that distinctive rattling noise, make it clear that both parts are likely failing. The cost breakdown shared is particularly useful for budgeting the repair. While 1470€ is significant, preventing further engine damage makes it worth addressing now. Will schedule the work for next week and have them replace both components at once to avoid having to pay labor costs twice. One final question before I book the repair, has anyone found any significant difference in performance between OEM and aftermarket catalytic converters? Want to make sure I make the right choice since this is a major repair investment for my Sharan.