2001 Infiniti QX4 P0420 and P0430 Codes: Cat Replacement Cost and ECM Reprogramming Solution

Hi everyone, My 2001 Infiniti QX4 failed its MA Emissions Inspection due to persistent P0420 and P0430 diagnostic trouble codes. After taking it to a Massachusetts-registered emissions specialist, the technician confirmed that both catalytic converters are faulty. He provided a Technical Service Bulletin (TSB) indicating that ECM reprogramming should be performed before replacing the catalytic converters. I’ve followed up with him to confirm whether he attempted this reprogramming or if only a dealership can perform it—however, he will not be available until next Monday. My vehicle is at 84,000 miles, which exceeds the 80,000-mile federal emissions warranty limit. Neither my dealer nor Infiniti Consumer Affairs has offered assistance. The cost to replace both catalytic converters ranges from $1,800 and higher, depending on the service provider. Interestingly, my Service Engine Soon (SES) light did not illuminate during this issue. Could this indicate an ECM-related problem that might be resolved through reprogramming? If so, is this procedure restricted to dealership-level technicians? Additional note: I replaced all four oxygen sensors a year ago, and after that work, the SES light turned off. Any insights or experiences with P0420/P0或430 on 2001 Infiniti QX4 would be greatly appreciated. Thanks in advance! Edit: For reference, I had all four O2 sensors replaced a year ago and the SES light went off afterward.