2001 Mitsubishi Galant OBD Codes P0421, P0141 (Duplicate) - Troubleshooting Guide

Model: 2001 Mitsubishi Galant Fault Code: P0141 Posted: 2005-08-13 12:03

I'm currently troubleshooting a check engine light on my 2001 Mitsubishi Galant with a 6-cylinder engine. The vehicle is displaying OBD II diagnostic codes: P0421 (Catalyst System Efficiency Below Threshold - Bank 1), and two instances of P0141 (Oxygen Sensor Circuit Malfunction - Sensor 1, Bank 1) — one active and one with a pending status. I'm seeking advice on the most likely causes for these codes. Can anyone provide insight into potential issues such as faulty oxygen sensors, exhaust system leaks, or catalytic converter performance? Thanks for any guidance.