Converter failures are fairly common on these vehicles, including the R51 Pathfinders and Xterras, but it seems to be hit or miss on the vehicles that have problems and I think the earlier ones are more prone than the 2007 and later, but that's just speculation from my mechanical experience and from the feedback I've heard on several Nissan forums. For example, my 2008 Pathfinder has 235,000 miles on it and still has the original catalytic converters on it (along with the rest of the exhaust). It came with the Laser Iridiums from the factory and I replaced them with the Laser Platinum 6240's at 100,000 and 200,000 miles. My 2006 Pathfinder has a different story. It originally came with the Laser Platinum 6240's from the factory which were replaced at 100,000 miles; it currently has 190,000 miles on it. I purchased the vehicle with 84,000 miles on it and the dealer had just replaced the left, upstream catalytic converter and upstream oxygen sensor (both genuine Nissan parts). At around 145,000 miles, it started triggering a P0420 code for the right converter, so, at 150,000 miles, I replaced the right, upstream converter with a Walker Ultra direct-fit converter. I also replaced the exhaust manifold with Doug Thorley shorty headers and replaced the rear converters with Doug Thorley mid-pipes, plus replaced the upstream, right, oxygen sensor (NTK brand). At around 175,000 miles, intermittently, I started getting a P0430 code for the left, upstream converter and it has been triggering more frequently as of late (I just erase the code when it pops up). Normally, this code doesn't indicate a clogged converter, rather an inefficient converter, meaning it is no long efficiently breaking down the exhaust emissions as per the ECM's inputs from the upstream and downstream oxygen sensors. It is usually safe to drive with inefficient converters...as long as they are not restrictive or clogged, which would result in drivability issues in most cases. The usual causes for a bad converter are excessive unburned fuel, either due to misfire, an over-rich condition or an oil burning engine. It's not uncommon on to hear of vehicles that have had an ignition misfire, such as that due to a bad coil pack, which is soon followed by catalyst efficiency trouble codes.
Let's go back to the failed converter issue seemingly more common on 05-06 models of the V6 Pathfinder/Frontier/Xterra... A friend of mine also had a P0430 code on their 130,000 mile Frontier. It was all stock, including the factory exhaust. One thing I always wondered about is why are the 2005 and 2006 models with the VQ40DE engine rated at 170 HP and 2007 and later are rated at 266 HP? Looking at my own 2006 and 2008 Pathfinders, I also notice that gas mileage is typically 1-2 MPG better on the 2008 model. Engine specs, including the cams, are the same between the two, as well as the intake system, tire size and transmission. My 06 does have the AUTO mode transfer case compared to the 08's manual transfer case and the so-called "restrictive Y" of the exhaust system is a little better design on the 08, but how much difference that makes, I don't know. They still shouldn't affect the factory power rating of the engine. So, either they incorrectly rated the engine horsepower and corrected it in 2007, or, more likely, they changed the fuel management software in 2008, perhaps making it run a little leaner than the previous software and better for the life of the converters? I don't know, but it's just my theory and food for thought!