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  #1  
Old 09-08-2013, 11:37 AM
dsurls dsurls is offline
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2002 Xterra
 
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Default Cause of P0420 on 2002 Pathfinder

I've had P0420 on and off the last couple of months, indicating an inefficient catalytic converter on Bank 1 (passenger side). So, I've been doing some research to determine the culprit of the problem, and I've run diagnostics using my OBDWiz software scanner.

If you look at the attached files, you can see a recent scan of the waveforms for the O2 sensors and the Short term Fuel % Trim values for both banks. Before running the scanner, I reset the code (only P0420 was showing) and ran drive cycles to get it ready for emissions testing. I ran the vehicle at idle at about 750 rpm for about 5 minutes, then at 2750 rpm for about 5 minutes, then back to 750 for about 2 minutes.

My initial take on these graphs is that the values look OK. I'm certainly not an expert, but the short term trim values seem reasonable on both banks. If anything, it looks like perhaps the downstream Bank 2 O2 sensor could be mirroring the upstream sensor a little too much, but it seems to settle down. But the Bank 1 values look pretty good, which is where I would expect to see mirroring with the P0420 code.

So, the question is, can anyone see anything wrong with these graphs that would signal a potential problem?

BTW, the vehicle is currently at about 175K miles, with a rebuilt engine at 160K. The catalytic converters are original.

Thanks for any suggestions you might have!
Attached Files
File Type: pdf Short-term % Trim Bank1 & Bank 2.pdf (27.4 KB, 4 views)
File Type: pdf Upstream O2 Sensor Bank1 & Bank 2.pdf (30.3 KB, 2 views)
File Type: pdf Downstream O2 Sensor Bank1 & Bank 2.pdf (26.2 KB, 2 views)
File Type: pdf Bank 1 O2 Sensors.pdf (28.2 KB, 3 views)
File Type: pdf Bank 2 O2 Sensors.pdf (28.5 KB, 1 views)
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  #2  
Old 09-08-2013, 09:13 PM
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NissanTech NissanTech is offline
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2004 Xterra
 
Join Date: Jun 2005
Location: California
Age: 52
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Quote:
So, the question is, can anyone see anything wrong with these graphs that would signal a potential problem?
Everything looks OK. Could be that there is not an actual problem right now.

Bad catalytic convert are a common problem on the Pathfinders, probably at some point your Pathfinder had bad gas, defective spark plugs, defective ignition coils, bad driving condition or a combination of all.
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  #3  
Old 11-05-2013, 07:06 PM
dsurls dsurls is offline
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2002 Xterra
 
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Sorry to be coming back so late on this, but I've recently discovered some other interesting findings. If I run a bottle of Techron and/or Chevron Regular with Techron thru a tank of gas, the CEL will often go off for a few days. It eventually returns, but if I fill up with Chevron again, the CEL will go off again. I used to use QuickTrip gas almost all the time because it is a "top tier" gas, but when I decided to try a bottle of Techron in it and noticed the CEL turning off, I've switched to start using Chevron.

So, does that lead to any specific conclusion? Is it more likely to indicate worn out O2 sensors, or bad catalytic converters, or something else?

Thanks again!
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Old 11-05-2013, 07:13 PM
dsurls dsurls is offline
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2002 Xterra
 
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Sorry to be late returning to this thread, but I've recently discovered something new related to this problem. If I run a bottle of Techron thru a tank of gas, or if I use Chevron gas with Techron in it, the CEL will usually turn off for a few days. It eventually comes back on, but if I repeat, the CEL will turn off again.

So, the question is, does this indicate a likely cause of the CEL coming on? Is it likely to be worn out O2 sensors, or indeed a bad catalytic converter, or something else?

Thanks again!
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