Honda Accord 2.0L P0420 Fault: Catalyst System Efficiency Below Threshold - Exhaust Leak Diagnosis
Hi, I recently diagnosed a Honda Accord (Reg Ck54 PDZ 2.0L) that has triggered Diagnostic Trouble Code P0420 — indicating 'Catalyst System Efficiency Below Threshold'. One of our mechanics initially suggested replacing the catalytic converter. After replacement, we discovered a leak in the flexi pipe near the exhaust manifold. We repaired the leak and reset the ECU codes. The vehicle ran normally at first, but after one week, the customer returned with the same P0420 code reappearing. Despite normal driving behavior, the check engine light is back on. Any suggestions for further troubleshooting or potential root causes? Thanks in advance.
Fixing the exhaust leak is critical — a persistent leak can cause incorrect oxygen sensor readings and trigger P0420 even after catalytic converter replacement. Ensure the flexi pipe connection is properly sealed and inspect for any cracks or loose fittings.