[smj999smj]

They tend to become inefficient over time, that's all. Yes, a bad running engine can ruin a converter, but sometimes they just go bad on their own. I've replaced both of my front converters on my 06 Pathfinder. Check with Rockauto.com; I believe Walker makes C.A.R.B. certified replacement catalytic converters that are a lot less expensive than genuine Nissan parts.

 

[smj999smj]

The C.A.R.B. certified aftermarket converters will come with a sticker that states they are such to be installed in the engine compartment. Looking at Walker's catalog, it doesn't look like they make C.A.R.B. certified converters for the 2005-11 Frontier V6. Your only option might be genuine Nissan or emission-certified, used converters.