Troubleshooting DTC P0420

Hi all, my check engine light came on while driving my 1999 Jeep Cherokee. I had the code read, P0420. The Jeep runs and drives great. Has 100,000 miles, burns no oil, or has any miss fires in the cylinders. I was told by Auto Zone that was any of the following.

catalytic converter needs to be replaced
oxygen sensor needs to be replaced AFTER catalytic converter
Large vaccum leak.

I do not hear a vaccum leak anywere so I guess that I am looking at either an O2 sensor or catalytic converter.

Has any one else had this problem? What did you do to solve it? I have to ask because neither item in able to be returned, I don't want to purchase the one that I do not need. Is there a way to test if the O2 sensor is bad? I see that the catalytic is welded into the exhaust, so that will require a cutting tool.

Thanks!

I had this problem for a while, after going through 3 o2 sensors and the code keep coming on, I finally check the o2 fuse located in the engine bay. Replaced that and everythings fine. So I'd say check that before going through the trouble of new sensors.

Is all your routine maintenance current ? O2 sensors can be tested, simply search or use the Google.

Most 4.0L Cherokees have a cracked exhaust manifold.

P0420 Possible causes:
- Three way catalyst converter Bank 1
- Exhaust tube leak
- Intake air leaks
- Fuel injectors may be faulty
- Fuel injector leaks
- Spark plugs may be faulty
- Improper ignition timing
- Engine Control Module (ECM)

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What does three way catalyst converter bank one mean?

outracing said:

What does three way catalyst converter bank one mean?

Click to expand...

Catalytic Converter. You only have one.