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Discussion Starter #1
I recently bought this truck used. The next day it threw the p0420 code. I changed the rear o2 sensor as many say to do. The code came back on 50+ miles later. Doing more research I have seen it could be an exhaust leak. So I went and looked at the exhaust and sure enough i found a leak in crap welds at the front of the muffler after the rear o2 sensor. My question is, would a leak at this location cause the code?

I have searched but found nothing clear about a leak at this location.
'02 3.4L
 

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Discussion Starter #3
F!
 

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It depends on how bad and where the leak is. O2 sensors have a clear air reference port that compares normal air to exhaust gas so there isn't much of a difference the O2 doesn't put out much of a signal. That being the rear O2, the ECU signals a cat failure.
It's usually easy to bench test an O2 sensor using a meter and a common propane torch.
Many sensors are replaced out of hand when there isn't really anything wrong with them when a quick test will tell if they are working well or not

I recently bought this truck used. The next day it threw the p0420 code. I changed the rear o2 sensor as many say to do. The code came back on 50+ miles later. Doing more research I have seen it could be an exhaust leak. So I went and looked at the exhaust and sure enough i found a leak in crap welds at the front of the muffler after the rear o2 sensor. My question is, would a leak at this location cause the code?

I have searched but found nothing clear about a leak at this location.
'02 3.4L
 

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It will if it's close enough and big enough to upset the sensor so that it is no longer reading the exhaust gas properly. Otherwise you'd toss the sensor and forget about it.
They basically work by comparing exhaust gas O2 in the atmosphere. That's why they all have a reference port to free air outside the exhaust. If the reference port gets plugged up with dirt and mud or something, that will also make it look like a bad sensor.

Exhaust leaks after the rear O2 sensor are no longer monitored and won't trip any sensors.
 

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Discussion Starter #7
I figured the O2 sensor needed to be replaced, the truck has over 250k on it and the o2 sensor seems factory. Denso from toyota printed on the sensor. The truck is at the shop now to see if its the cats. If it is Im going to order the URD sim.
 

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Some will argue against the URD sim and say just do an OEM fix.

The URD fixed my P0420 and I haven't had any issues in years.
 

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I do a lot of off roading in my 96 2.7 and between the mud and bouncing around I could never keep an O2 sensor from trippin. I'd either crack a weld or plug it up or what ever. The main thing is it really never effected me besides having my engine light on. But i also only ever did OEM repairs so if you think you can fix the issue with after market and be done with it try it out.
 
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