P0420 Fault on 1998 Honda Accord: Causes and Solutions at 94K Miles
Hi. My 1998 Honda Accord reached approximately 94,000 miles recently, and the Check Engine light has come on with fault code P0420. I previously replaced the catalytic converter around 60,000 miles based on dealer recommendation — but now I'm concerned that an original Honda cat might not last this long. Given the P0420 code, which indicates a failure in the catalytic converter's efficiency, I’m considering replacing the oxygen sensors as a potential fix. However, I’d like to know if there are other root causes or diagnostic steps. The issue appeared shortly after my car stalled unexpectedly and was towed to a nearby shop. They replaced the alternator’s distributor cap and rotor. A few days later, the Check Engine light turned off. Could this repair be related to the current P0420 code? For instance, could a misfire or electrical interference from that work have affected emissions sensor readings? Any insights on how to properly diagnose and resolve this issue would be greatly appreciated. Thanks, Rbfhome
How is your car running currently? At 94,000 miles, a full engine tune-up with new spark plugs and plug wires is recommended. A misfire can damage the catalytic converter over time. If the vehicle runs smoothly, consider inspecting the front oxygen sensor located in the exhaust manifold — it can become sluggish. When this happens, the ECU detects that the rear O2 sensor voltage closely follows the front one, triggering P0420. Here's a helpful resource on cat failure: http://www.troublecodes.net/articles/catfailure/. Hope this helps — Mike