Hi Scotty, I have a 2015 Mercedes C300 with 65k miles. I bought it last May with 50k miles and the Check Engine light came on in July, they replaced the Catalytic Converter and PCV Valve under warranty.. now the light is back on and with my scan tool showing the Cat again.. I’ve done some research and seen these engines have (unburnt) oil issues in a cylinder and or (cracked) piston issues and might need to have the engine replaced but Mercedes doesn’t honor it. My mechanic won’t touch a German car and Mercedes in my area isn’t very helpful. And tips on how a average person might dig deeper into the issue with little help from Mercedes?
Clarification: Can you list the code(s) that showed up?
PO420
You really need to find an independent mechanic that specializes in those cars. They'll be expensive but better than the stealerships.
You need a European car mechanic. They are worth their price. Those engines are known to have serious issues and replacements are $$$$$. I would look for a local Euro mechanic near you.
Do all the research you can but don't expect any help from Mercedes.
What’s the exact code number?
PO420
Sounds like I have a lot of things to check out..
I think it's better than spending a gazillion dollars on replacement CATS that don't seem to solve the issue.