H3 P0420

[lowtrac]

I'm fighting a P0420. I replaced the rear o2 sensor about six months ago and the code came back. After a while, the downstream cat clogged. It was broken inside, so I cut it out and had a new cat welded in which I expected to be the real issue. Cleared the codes and the P0420 came back. I went ahead and put a spacer in on the rear o2 sensor and I've been driving it around to see if the code clears on its own. It hasn't so far. Does anyone know what voltages are normal for the front and rear o2s?

 

[Jeepwalker]

I'll let others answer the O2 voltage question, but double-check your intake/exhaust manifold bolts for tightness or any leaks in that area. Sounds simple, but on a variety of vehicles they often loosen up and can cause downstream issues. Have you done a vacuum check ..if so what does it look like? Did the catalytic converter seem plugged up with hard fuel, or oil deposits? What fuel are you running (top tier?)? Any other additives? Does it smoke when started up in the morning ..or hard starting?

 

[lowtrac]

I'll let others answer the O2 voltage question, but double-check your intake/exhaust manifold bolts for tightness or any leaks in that area. Sounds simple, but on a variety of vehicles they often loosen up and can cause downstream issues. Have you done a vacuum check ..if so what does it look like? Did the catalytic converter seem plugged up with hard fuel, or oil deposits? What fuel are you running (top tier?)? Any other additives? Does it smoke when started up in the morning ..or hard starting?

The cat was broken inside and rattling. No startup smoke or anything. There was a very noticeable loss in power when the cat clogged. I can’t hear any exhaust leaks.

It had a P0136 code stored yesterday along with the P0420 so I swapped the rear sensor again this morning. Currently the P0136 and the pending P0420 along with the freeze frame data are clear. It has a P0420 still stored, but the MIL is off. I’m hoping that’ll clear out after another drive tomorrow.




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[lowtrac]

Here’s a short video showing the live data from the O2 sensors. I’m calling this “normal” since the codes seem to be clearing out.

https://youtu.be/v3-diDUNNAg


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[alrock]

Everything resolved?

 

[lowtrac]

Everything resolved?

Yep. Passed emissions test yesterday. It still has a history P0420 stored, but apparently GA testing only cares about current codes.

They’re also ok with one I/M monitor test not being complete. I presume that would most likely be Evap.


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