My car has thrown two CEL codes in the past 3 weeks, P2A00 (Air Fuel Ratio Sensor Circuit Range/Performance Bank 1 Sensor 1) and then P0420 (Catalyst System Efficiency Below Threshold Bank 1) a week later. Both times I was driving steadily on the highway for a while when the code came in. When the second code came in, the original P2A00 code didn't re-appear.

An exhaust leak seemed a possible culprit, so I first checked the length of the exhaust with a stethoscope. I didn't see, feel, smell, or hear any leaks. I'm pretty sure that there weren't any major leaks, but can't fully rule out a tiny one that would need a smoke test to find.

My next guess would be replacing the bank 1 upstream O2 sensor. It seems that sensor is one of the other things that could cause both of these codes. I didn't notice much difference in the bank 1 to 2 OBD reader live data reading when idling or revving stationary, but I haven't roped my wife into helping me check those readings on the highway yet. Or does it giving generally reasonable data mean it is functioning properly?

Is replacing the bank 1 upstream O2 sensor the next step? Or is there something else I should check first?

thanks,
Matt

 

sounds like your catalyst may be coming apart. i wouldnt just throw an upstream o2 sensor because its not going to help especially if the catalyst is deteriorating internally. cats are covered under 8/80 emissions warranty.

 

Check for vacuum leaks

 

It took a while for the CEL to come back so I could take it to the dealer. Infiniti replaced the cat under warranty today. Thanks!