Quest exhaust treatment malfunction

I had a similar issue with my Quest. Rough running and a strong smell, though no visible leak. Have you checked the lambda sensor? Sometimes a faulty sensor messes up everything downstream, like the catalytic converter and EGR valve.

That's an interesting analogy. The lambda sensor wasn't my first thought. Did you have the same symptoms? And was it difficult to diagnose?

Yes, same symptoms. It took a while to pinpoint because the catalytic converter was initially suspected. Best to get it checked at a workshop; they have the tools to diagnose it properly. It's better to leave it to the pros.

Thank you for the advice. I'll take it to a workshop for diagnosis. Turns out the lambda sensor was defective, as you suspected. Repair cost 375€. Appreciate the help!