1998 Dx code P0420

[HondaGirl02]

Okay so I've got a 1998 Civic DX, the CEL came on. I went to auto zone and had them pull the code, which came up with the P0420, the printout that they gave me said it could be any of four possible problems. One of the possibility it said is the Ignition system, which about a year ago, I had to have the ignition switch (I believe) changed. Is it possible, that when the mechanic fixed that, something else got messed up and the code is just now starting to show. Or is it more likely that my cat converter is gone bad. Any help would be appreciated. Thanks

 

[WantACivic]

Heres a rundown of things you can check before writing off the Cat as malfunctioning:

* An oxygen sensor is not reading (functioning) properly
* The engine coolant temperature sensor is not working properly
* Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
* Retarded spark timing
* The oxygen sensors in front and behind the converter are reporting too similar of readings

Possible Solutions

Some suggested steps for troubleshooting a P0420 code include:

* Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
* Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
* Inspect the downstream heated oxygen sensor (HO2), replace if necessary
* Replace the catalytic converter