P0420 Catalyst Code

triz

Original poster
Member
Apr 22, 2013
746
I got this code yesterday. Trailblazer has approximately 145k miles. Have never changed the 02 sensors. I did get a code for the front 02 many thousand of miles ago. Changed it to another non OEM and then switched it back to the previous O2 sensor. Code never came back. I do have a K&N filter that I haven't yet cleaned yet. Will swing by and pick up a infrared thermometer possibly later on and get before and after cat temps.

My take. Front O2 looked really lazy, Post O2 cat seemed pretty steady.

Video uploading:

http://youtu.be/qoCd2I0CfI0
 

MAY03LT

Member
Nov 18, 2011
3,412
Delmarva
I don't trust o2 voltage since most volt displays don't refresh fast enough to give an accurate view of the data. Even my tech2 is like molasses on o2 data volts but when I graph it it's fast. But It did look like the upstream was sticky at least twice. I'll check my notes at work tomorrow for any diy friendly tests.
 

triz

Original poster
Member
Apr 22, 2013
746
Took a chance based on what I thought was a bad O2 sensor from the readings on my code reader. I changed the O2 sensor based on what looked like to me a very lazy O2sensor. I did not clear the code and wanted to see if it would clear on its own. It has.

So it looks like a custom Borla and cat is out right now.
 

triz

Original poster
Member
Apr 22, 2013
746
So its back again. P0420 @165K miles. Took it to have the cat replaced and the guy from the shop said the cat looked fine not rattling or broken inside, good back pressure flowing. He suggested replacing the coil packs.

I'm going to get rid of the K&N filter and go back to a dry filter, clean the MAP and TB. The truck went into limp mode twice. Shut off right inside the work parking lot. No other codes for misfires but I found a pending for a Torque Conv CKT perf/lock?

Transmission guy says that code won't make it go into limp mode. Lots of diagnosing this week.
 

MAY03LT

Member
Nov 18, 2011
3,412
Delmarva
Did the guy watch 1 and 2 o2 sensor data? That's the only data that I trust.
 
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triz

Original poster
Member
Apr 22, 2013
746
I have not yet. The previous 02 sensor up front was replaced 20k miles ago and the light went off on its own. I think something else is amiss because its been starting rough + all the above.
 

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