P0420 Fault on 2007 Nissan Altima 3.5L 6-Cylinder: Is Cat Replacement Necessary or Are There Alternatives?

It's important to check your state's specific smog inspection regulations, as they may vary. If the dealership has concluded that the catalytic converter (cat) is faulty, it likely means they've ruled out other potential causes like oxygen sensors or exhaust leaks. I'd recommend holding them accountable for a retest if replacing the cat doesn't resolve the issue. Is your vehicle high mileage? Does it run smoothly otherwise aside from the P0420 code? Has the P0420 code been present consistently since it first appeared? Some users have reported success using exhaust system cleaning products, especially if the error is intermittent. However, results vary. If there are no other related OBD-II codes or abnormal fuel trim values, and oxygen sensors are functioning properly with no visible exhaust leaks, then catalytic converter efficiency becomes a strong suspect. Additionally, there was an official emissions recall for 2007 Nissan Altima models (ID# PC 131) involving the exhaust manifold. I recommend checking this recall and having it inspected or repaired if applicable.

Thanks for the helpful input! I've already tried several exhaust cleaning products, but none have resolved the issue. The car runs fine overall—no performance issues—and has done so for months with only the SES light on. It's now been consistently showing the P0420 code for the past two months. This consistency makes me question whether a faulty catalytic converter is truly the root cause, especially since the vehicle still performs well. I'll definitely look into that 2007 Altima recall (ID# PC 131) and verify if it applies to my model.