Hybrid Passat Exhaust Leak + Rough Running Fix Needed

Had similar issues with a 2015 VW Golf GTE hybrid. The malfunction turned out to be a failing NOx sensor combined with a defective Lambda oxygen sensor. The engine light came on intermittently at first, then stayed constant. The exhaust smell and rough running are typical symptoms when the engine runs too rich due to incorrect fuel mixture readings. The garage diagnostic revealed the Lambda sensor wasnt providing accurate readings to the ECU, causing increased emissions and poor performance. The repair involved replacing both sensors and cleaning the EGR valve, which had carbon buildup from the rich running condition. This is a fairly serious issue that needs prompt attention, as it can damage the catalytic converter if left unchecked. The symptoms match what you describe, rough running, engine light, and exhaust issues. Recommend getting a proper diagnostic scan before replacing parts. A faulty oxygen sensor will show specific fault codes that help pinpoint the exact problem. Quick tip: when these sensors fail on hybrids, the system often defaults to a protective mode that causes the symptoms you mentioned. The sooner this gets checked, the better chance of avoiding catalytic converter damage.

Thanks for sharing your experience, glad you got it sorted. I had those exact symptoms on my 2018 Passat last winter. The engine light came on and rough running started suddenly during a cold morning. The exhaust pipe was leaking around the flex joint and the EGR valve ended up being completely clogged. Did you keep track of the repair costs for the sensor replacements? Also curious if youve had any other issues pop up since getting it fixed? My DEF fluid system started acting up a few months after the repairs, though that was probably unrelated.

Thanks for asking about the follow-up. After having the Lambda oxygen sensor replaced for 375€, the exhaust treatment malfunction cleared up completely. The diagnosis was spot-on, it was sending incorrect readings to the ECU causing the rich fuel mixture. The repair has held up well with no recurring issues. Unlike your situation, my EGR valve only needed cleaning rather than being fully clogged, and the NOx sensors have been functioning normally since. The exhaust system has been running clean with no warning lights or performance issues for the past several months. Your DEF system issue does sound unrelated, as the oxygen sensor malfunction typically affects fuel mixture and emissions control rather than the DEF injection system. The particulate filter has also been working as intended since the repair, with no buildup or regeneration problems. If your DEF system is acting up, might be worth getting the NOx sensors checked, as they can sometimes trigger DEF-related warnings when failing. But in my case, fixing the faulty oxygen sensor resolved all the initial symptoms completely.

I finally got my Passat fixed after discovering multiple issues. After getting quotes from several shops, I found a certified hybrid specialist. The diagnostic scan revealed both a failing oxygen sensor and an exhaust leak at the flex pipe, exactly what you experienced. The repair bill came to 890€ total, including parts and labor. They replaced the oxygen sensor, welded the exhaust leak, and thoroughly cleaned the EGR valve which was heavily clogged. The mechanic showed me the carbon buildup they removed. Since the repair three months ago, the engine runs smooth with no check engine lights. The exhaust smell is completely gone and fuel economy has improved. Only lingering issue is an occasional DEF fluid warning, but the mechanic thinks thats probably due to a dirty NOx sensor that will need attention at the next service. Much better experience than my previous mechanic who just wanted to replace the entire catalytic converter without proper diagnosis. Lesson learned, finding a qualified shop that specializes in hybrids made all the difference.

Hello, I have installed a new catalytic converter. Now I get the following message: Catalyst system bank 1 efficiency too low. Could the error also be due to the lambda sensor? E.g., due to cable damage during the conversion. Or maybe the new cat from the internet doesn't perform? Thank you in advance

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It's possible that the error could be related to the lambda sensor, especially if there was any damage to the wiring during the installation. A faulty or damaged lambda sensor can provide incorrect readings, leading to the "catalyst system efficiency too low" message. I recommend checking the sensor's wiring and connections for any signs of damage or disconnection. If everything looks intact, consider performing a diagnostic scan to see if the sensor is functioning correctly. If the sensor is fine, the issue might be with the catalytic converter itself, especially if it's an aftermarket part. Let me know how it goes or if you have any further questions.