I have a 2010 Nissan rogue S Krom AWD with 151,000 miles. Last weekend, I drove to Cincy and back (total of 160 miles). On my way back I stopped at a red light. When the light turned green, my car went into limp mode so I pulled over, killed the engine, waited 5 mins, started it up, and it drove like normal. Long story short, I’ve had a P0420 code since last year and that’s the only code I have now. Before I bite the bullet and replace the front cat with exhaust manifold, what are some ways to confirm the cat needs to be replaced?

Thank you!

P0420 by itself will never cause a limp, so no one can tell you anything about your current issue unless you post the new codes that came up. That said, P0420 by itself is a harbinger of a dying cat, and driving around like that can be very dangerous on a QR25 engine. The best that can happen is that the cat disintegrates and blocks your exhaust, the worst is that your engine inhales the debris and it's bye-bye engine. See this post for some pics of what can happen:
engine-and-transmission-swap-t632989.html

Have you taken a moment to read the previous posts on this topic?
2009 Rogue - P0420 Code
2011 Nissan Rogue Krom AWD CEL & P0420 Code
The Dreaded P0420 Code
Is my catalytic convertor shot?

PS - If there weren't any additional codes after it stalled, the prime suspects would be your cam and crank sensors. Unexplained stalling without codes is a hallmark of dying Hall sensors.

Thanks for the response! No additional codes so I’ll take a look at the cam and crank sensors. Going to go through with replacing the cat as well.

I had that same P0420 code on my 2010 Ford Fusion about 3 months ago. I also had a "Bank 1 O2 sensor fail in lean position" code. or something similar to that verbiage. I can't recall what that exact code# was...but after I ended up replacing both the upstream and downstream O2 sensors, reset all the codes, I have not had any more codes come back and engine runs like new. No more P0420 code.

FWIW, I was also right at 100,000 miles on the original spark plugs so I went ahead and changed those as well.

P0420 with A/F or HO2S codes is a different story than P0420 by itself. With no other codes, P0420 practically always means a dying cat. However, most ECM's (including most Nissans) cross-check the wideband sensors in front against the HO2S's in the rear. That can fool the ECM into blaming the wrong culprit, which will usually turn out to be a flatlined HO2S.