Chevrolet Kalos Exhaust Smell Rough Running

I had similar symptoms on my old Renault Megane. Check engine light, rough running... turned out the catalytic converter was failing. The unburnt fuel was causing the strong smell and leak. The catalytic converter’s job is to convert harmful pollutants in the exhaust gas to less harmful ones, like carbon dioxide and water vapor. A failing converter won't do this properly, hence the smell and rough running due to backpressure.

So, with the Megane, did you notice any difference in fuel economy or hear any strange noises before the catalytic converter completely failed? I'm trying to rule out other exhaust-related culprits like the exhaust pipe itself. I don't think my Kalos uses DEF.

Fuel economy definitely took a hit, and there was a rattling noise coming from underneath the car, especially when the engine was cold. It's hard to diagnose exhaust issues remotely, but given the symptoms, I'd recommend taking it to a workshop for a proper diagnostic. They'll be able to pinpoint the problem much faster, and they have the right tools.

You were right! Took it to the shop, and it was indeed the lambda sensor, which in turn damaged the catalytic converter. Ended up costing me 375€ to get it all sorted. Thanks for pointing me in the right direction!