P0420 Code on 2006 Accord
 

Greetings all,
I am new to the forum and would like to pick everyone's brain on a current issue I am having on my 2006 Accord EX 4 cylinder with AT. A few weeks ago CEL came on. Used a scan tool and it read code P0420 or P420. Basically a catcon inefficiency. I looked under car and found my O2 sensor wiring harness hanging down and the protective cowling broken (must have hit some heavy snow or ice). I replaced the wiring cowl and re-secured all wiring, did not observe any damage to the wiring or sensor. After I finished the CEL went off for several days then came on again. Showing same code, so I unplugged the O2 wiring connector under the passenger seat and re-checked with same code results. I really think there has to be an issue with the 02 sensor but are there other tests that I can do to see if the sensor is bad probably due to some shock damage? The sensor connects directly to catconv and is easily accessible, however likely to be seized, any suggestions to prep before removal? Probably will also need a special 02 sensor removal socket? Thanks in advance for any help!!!!

The code P0420 is a code for catalytic converter efficiency below normal. It does not directly imply that secondary (catalytic converter sensor) O2 sensor is faulty or damaged. Damage to the O2 sensor wiring or sensor would set other codes, P0137, 0138, 0139, or 0141.

Only way to know for certain is to monitor O2 sensor performance w/ an obd2 scanner that can display O2 signals or simply replace the sensor. If O2 sensor signals are good, something else is causing the code; perhaps an exhaust system leak or damaged converter.

Shake the converter vigorously and listen for any rattling. This would indicate the converter matrix is damaged and new converter is necessary. Exhaust leaks can cause P0420 also. A good way to check for exhaust leaks is to use Seafoam into the engine through a vacuum line and inspect exhaust for smoke leaks (seafoam creates lots of smoke).

A new OEM catalytic converter is expensive so its worth some effort to insure problem is harness rather than converter.

good luck

Thank-you
 

Thanks for the info I will try these and see if I can figure the cause. One additional question, if I unplug the 02 sensor shouldn't it throw a different code? I unplugged the sensor form inside the car and it did not trigger a new code. Thanks again!

Yes, it should show several codes for O2 sensor heater circuit and O2 sensor circuit. If not, ECU may be faulty.

good luck