Mercedes ML exhaust issues and repair

Sounds familiar. I had a similar issue with my ML, though I can't remember the exact codes. A dodgy oxygen sensor can definitely mess things up. Have you checked for any obvious cracks or damage in the exhaust manifold? An exhaust leak before the sensor can also throw off readings. It's worth a look before you start swapping parts. Just curious, have you noticed any changes in fuel economy?

Good call on the exhaust manifold, I'll give that a once over. Fuel economy has been slightly worse, yeah. If the manifold is fine, is replacing the oxygen sensor a straightforward job, or is there anything tricky I should watch out for? I'm trying to avoid messing with the EGR valve or particulate filter if I can help it.

Replacing the O2 sensor isn't too bad, usually. Just make sure you get the correct one for your engine, and be careful not to overtighten it when you install the new one. But honestly, given the exhaust leak and rough running, it might be worth getting it checked professionally. A proper diagnostic scan could pinpoint the issue, especially if it's something else entirely. Could save you money in the long run. I ended up going to a workshop. They sorted the O2 sensor but also spotted a small crack in the exhaust which was causing the leak.

Thanks for the advice. I inspected the exhaust manifold, and I think you're right, there is a crack that I missed. I took it to a shop, and they confirmed the lambda sensor was defective and the exhaust had a crack. They replaced the sensor and did some welding on the exhaust. The repair cost me 375€. The car is running smoothly again.