VW Transporter Exhaust Leak Causing Engine Issues

Had similar issues with my VW Passat 1.8T from 2004. The rough running and check engine light pointed to an exhaust leak around the Lambda sensor, which was causing incorrect air-fuel mixture readings. The exhaust leak near the sensor created false readings, making the engine run rich. This explains the strong exhaust smell you mentioned. The Lambda sensor needed replacement, plus the exhaust pipe section around it had corroded and created the leak. Mechanics needed to cut out the damaged exhaust pipe section and weld in a new piece to ensure proper sealing. In your case, the symptoms match exactly, rough running, exhaust smell, and CEL are classic signs of an exhaust leak affecting the sensor readings. This is a fairly serious issue since it affects emissions, fuel economy, and engine performance. Left unfixed, it can lead to catalytic converter damage. The repair requires proper diagnostic equipment to verify the sensor values and pinpoint the exact location of the exhaust leak. A trusted mechanic should: Perform proper exhaust leak testing, Check Lambda sensor readings, Inspect the entire exhaust pipe for additional damage, Test the system after repair to ensure proper operation Looking at your vehicles age and mileage, this is a common wear point for the exhaust system components.

Thanks for that detailed reply about the exhaust pipe issue. Your Passat had almost identical symptoms to my Transporter. Really glad you confirmed my suspicions about the oxygen sensor being the main culprit. Would you mind sharing what the total repair cost was for fixing the exhaust leak and replacing the sensor? Also curious if you had any related problems pop up since the repair, like EGR valve issues or particulate filter problems? Just want to budget properly and know what to watch out for going forward. Sounds like I definitely need a mechanic who can do proper diagnostics and welding work for the exhaust system. The malfunction needs fixing before it causes more expensive damage.

Good news, took my Passat to a mechanic and got everything sorted. The exhaust treatment malfunction warning disappeared right after they replaced the defective Lambda sensor. Total bill came to 375€ which included the diagnostic work and sensor replacement. Since the repair was completed three months ago, the engine has been running smoothly with no check engine lights or exhaust issues. Have not experienced any problems with the catalytic converter or other exhaust components. The proper diagnosis prevented any cascade failures that could have affected the particulate filter or other parts. The key was finding a shop with the right diagnostic equipment to accurately pinpoint the oxygen sensor malfunction. Getting it fixed promptly helped avoid more extensive exhaust system damage. The repair cost was worth it considering how much better the car runs now. No additional issues have emerged since the sensor replacement. Just make sure whoever works on your Transporter uses quality parts and properly tests the system after repair. A proper fix should resolve the symptoms completely like it did in my case.

Thanks for the input. Finally got my Transporter fixed! Found a mechanic specializing in VW repairs who took the time to properly diagnose the issue. The oxygen sensor was indeed faulty, plus there was a cracked section of the exhaust pipe that needed welding. Total repair came to 450€, a bit more than expected but worth every cent. They replaced the sensor, welded the damaged exhaust pipe section, and ran full diagnostics to ensure everything was working correctly. The engine light is now off and the rough running is completely gone. The mechanic also checked the entire exhaust system and confirmed no issues with the catalytic converter or other components. Really relieved I got it fixed before any serious damage occurred. The car runs like new again, no more exhaust smell or performance issues. One word of advice for others with similar problems: dont wait too long when you notice exhaust leaks. Getting prompt repairs from a qualified shop saves money in the long run and prevents bigger problems.