I got the P0420 CEL code for system efficiency. I want to make sure my cat is actually bad before I put any money down to buy a new one. Are there things I can check or certain symptoms I can look out for? One thing I noticed since I got the CEL is that my truck has had a lower idle, especially when I first start my engine.
Another question, I've recently used Seafoam in my oil and fuel. Do you think the carbon build-up that the Seafoam cleaned is clogging my cat, which is what triggered the CEL?