I was thinking about moving out of my 73K mile '07 CL600 to an S-Coupe and trying to get it ready to sale. I've done coil packs (V12icpack), upgraded the voltage transformer to the V12icpack boost box, motor mounts, and brake rotors. My check engine light came on an it seems that the right cat needs to be replaced + O2 sensors. Before I spring for the OEM cat are there aftermarket alternatives that work better?

 

Do you know what might have caused the catalytic converter to fail?

 

Catalytic converter failure is usually a symptom of some other problem (but not always). Engine running too rich can melt them, incorrect fuel etc. Changing it might not resolve any issues or stop a check engine light appearing. Have you had any other codes recently or long term ones?

 

Here is a really good video on how to diagnose a cat failure properly. At least then youll be confident thats the problem and not just a pair of dodgy O2 sensors or something like that. His methodology is very good.