The old PO420 question

**jmsgtp04** · 11-05-2014

I have read through some of the old posts and was looking to find out if anyone has seen where you get a PO420 code even after checking the Cat and it seems Good? I've replaced both 02 sensors and the Ck eng. light still comes back. It is the only code in the system, as well. I checked the CAT with a infared temp gauge and the Code Scanner live function(02 sensor 2 voltage). The car has always ran fine. I personally really don't give a sh*t about the code, it's just that I may sell or trade this thing soon and don't need to get screwed over the Ck eng. light being on. Any help would be greatly appreciated. Thanks

**Fivefingerdeathpunch** · 11-05-2014

I would try the "Non fouler" trick and extend the o2 sensor so it's further away from the exhaust gases.

The cat may not look bad, sound bad, smell bad but o2 sensors are very sensative to changes in oxygen, so if it goes out of the limit it will set the light, even if it's only by a small amount.

**jmsgtp04** · 11-05-2014

should it be a straight or a 90 degree (non-fouler)? Thanks

**nik12937** · 11-05-2014

The straight ones work just fine, I use them myself to avoid setting the code. Drill one out with a 1/2" drill bit, screw the O2 into it, and then screw that assembly into the unmodified non fouler.

**Impala131** · 11-06-2014

If it's the stock cat, and you have new O2 sensors... doesn't that kind of point to a bad cat? Assuming you used the Delco/Denso O2 sensors.

I think the O2 fouler will help with the code, but if it is a bad cat, and further deteriorates... won't that eventually cause driveability issues?

**jmsgtp04** · 11-07-2014

Thanks (all) for the help, I'll try the fouler. I don't believe its a bad cat and I hoping to sell this thing next spring anyway.

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