Renault SM5 Engine Light and Exhaust Leak

Sounds familiar! I had a similar issue with my 2018 Opel Insignia – engine light, rough running, and a whiff of exhaust fumes. In my case, it turned out to be a faulty lambda sensor. The ECU was getting bad data, messing up the fuel mixture. Have you scanned the car for error codes? That would be my first step. Check the O2 sensor readings too, if you can. Disconnecting the battery for a few minutes might reset the light, but it will come back on. Don't ignore the exhaust leak. It can damage your catalytic converter!

Thanks for the quick reply! I did use a cheap OBD2 scanner, and it threw up a generic code related to 'exhaust treatment malfunction'. I wasn't sure how specific that was. Where exactly was the lambda sensor located on your Insignia? And did you notice any drop in fuel economy?

That generic code confirms a problem in the exhaust treatment system. On my Insignia, the lambda sensor was located right before the catalytic converter, screwed into the exhaust pipe. It's easy to spot. I would bet that your SM5 is very similar. Yes, my fuel economy went down about 10-15% when the sensor started failing. Given the exhaust leak and the 'exhaust treatment malfunction' code, I'd strongly suggest taking it to a workshop to have it properly diagnosed. You don't want to risk damaging the cat. Remember a defective sensor can overheat and damage your catalytic converter.

Thanks so much for the advice! I really appreciate it. I took it to the workshop, and you were spot on – it was the lambda sensor. The exhaust leak was also from a corroded joint, as I suspected. Total repair cost was 375€, including a new sensor and fixing the exhaust leak. Runs like a charm now! Thanks again for the help.