Buick LaCrosse Exhaust Leak Causing Multiple Issues

Had a similar issue with my 2017 Buick LaCrosse hybrid last year. Having some experience with hybrid vehicles, I recognized these symptoms as potentially serious exhaust system issues. The check engine light and rough running turned out to be caused by a faulty oxygen sensor, which was affecting the fuel mixture and causing poor performance. Initially thought it might be the EGR valve or catalytic converter due to the strong exhaust smell, but diagnostic testing confirmed it was specifically the lambda sensor malfunction. Took it to a workshop where they ran a full diagnostic check first. The repair took about 3 hours total and cost 375 Euro for parts and labor. After replacement, the engine ran smoothly again and the exhaust smell disappeared completely. To help diagnose your situation better, could you share: Current mileage on the vehicle, Any error codes showing up, Whether the issue happens more during cold starts or when the engine is warm, Any recent maintenance or repairs done besides the particulate filter service, Type of fuel youre using These details would help determine if youre facing a similar oxygen sensor issue or if its related to other components in the exhaust system.

Thanks for the detailed feedback. My current mileage is 154084 KM and the last major service was the particulate filter maintenance. I did get the error codes checked, its showing P0420 which points to a catalytic converter efficiency issue. The problems are definitely worse on cold starts, and the exhaust pipe seems to have a small crack near the connection point. Also noticed the DEF fluid level warning came on recently, though Im not sure if thats related. Been using regular gas as recommended by the manual.

Based on that P0420 code and your description, this is likely more serious than the oxygen sensor issue I dealt with last year. While my LaCrosse had similar symptoms, the crack in your exhaust pipe combined with the catalytic converter code suggests multiple problems that need addressing. The exhaust leak is definitely contributing to the strong smell and rough running. The catalytic converter malfunction could be causing the efficiency code, but the leak might be making the readings worse. In my experience with these hybrids, a failing catalytic converter often shows these exact symptoms, rough cold starts, exhaust smell, and deteriorating performance. When I first suspected my catalytic converter issues, I delayed repairs thinking it was just the sensor. That was a mistake, the problem got worse and ended up damaging other components. The DEF fluid warning might be indirectly related, as the exhaust system malfunction can affect various sensors readings. I would recommend getting both the exhaust leak and catalytic converter checked immediately. The particulate filter service you had might not have addressed underlying issues with the catalytic converter, which typically starts showing problems around your mileage point. What type of driving do you typically do? Short trips with cold starts can accelerate catalytic converter wear, which is what happened in my case.

Current mileage is 154084 KM, and youre right, my driving patterns could be contributing to the issues. I do mostly short commutes with lots of cold starts, which probably isnt ideal for the system. After checking the codes and hearing your experience, Im convinced this needs immediate attention. The P0420 code, combined with the exhaust leak and rough running during cold starts, points to multiple issues that need fixing. The recent DEF fluid warning and engine light definitely add to my concerns about potential damage to other components. Going to schedule a repair visit this week rather than risk more damage. My particulate filter service clearly didnt catch these developing problems. Will have them check both the catalytic converter and that exhaust pipe crack, plus run a full diagnostic to check for any NOx sensors or other exhaust system issues that might have been affected. Appreciate the warning about how delaying repairs made your situation worse. Better to address it now before it leads to more extensive damage.