Nissan pathfinder le 2006 with P0300 detected and suspected bay 1 catalyst bad.

Please check out these videos of O2 sensors being scanned with Delphi DS150E scanner tool. I am wondering if anybody worked with this tool. Is it too slow to refresh to catch O2 sensors switching, or my O2 sensors are not switching?

I also noticed that the sensors are only switching within 100 mVolts and that B1S1 and B1S2 have similar voltage. Does this indicate bad catalyst?


O2 sensors, long term short term fuel trim on cold start engine https://www.youtube.com/watch?v=pkGP7liPLu8

O2 sensors, long term short term fuel trim on warmed up engine https://www.youtube.com/watch?v=fiibRidYWF4

O2 B1S1 and B2S1 graphing on warmed up engine https://www.youtube.com/watch?v=G5UePOapA3E
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Just a couple of notes.... The front sensors are actually air/fuel ratio sensors and not technically "oxygen sensors." Air/fuel sensors, which look just like oxygen sensors and are usually labeled as such by parts vendors, are more accurate but also operate on a much narrower band. Whereas an oxygen sensor can operate from 0v. to 1.1v, an air/fuel ratio sensor typically operates within a range of 400-600 millivolts. Air/fuel ratio sensors and oxygen sensors should be checked with the engine fully warmed up. Checking operation at idle won't tell you much; it's best to view graphing at 2000+ RPM. When checking upstream to downstream frequency ration, to determine catalyst efficiency, you need to be viewing the information while driving at highways speed during a steady cruise. Because of safety reasons, this is obviously best done with two people, one driving and one watching the scan tool info. It's not that easy to test catalyst efficiency by using a scan tool. The ECM will typically let you know if one or both are inefficient by setting a P0420 and/or P0430 code(s).

Hi SMJ,

I've had a nagging P0430 code for the last 6 months or so.

In your experience, can this be caused by a bad secondary O2 sensor? Only reason I ask is that when I check the voltages at 2000rpm, the voltage on the rear O2 sensor on the one side is all over the place, from 0.1v to 0.9v, but the Front sensor seems to be fine, at a stable 0.6v.

I've never changed the rear sensors, but did the front sensors about 30k miles ago.

Everything else seems normal. Performance, exhaust smell/appearance, fuel economy, etc. But I've also heard the horror stories of degraded catalysts getting sucked into the exhaust valves... Would rather avoid that...

t

disallow wrote:Hi SMJ,

I've had a nagging P0430 code for the last 6 months or so.

In your experience, can this be caused by a bad secondary O2 sensor? Only reason I ask is that when I check the voltages at 2000rpm, the voltage on the rear O2 sensor on the one side is all over the place, from 0.1v to 0.9v, but the Front sensor seems to be fine, at a stable 0.6v.

I've never changed the rear sensors, but did the front sensors about 30k miles ago.

Everything else seems normal. Performance, exhaust smell/appearance, fuel economy, etc. But I've also heard the horror stories of degraded catalysts getting sucked into the exhaust valves... Would rather avoid that...

t

Yes, my understanding is that the threat of bits of converter's core getting sucked back into cylinders causing smoking engine are very real only when the core is broken apart. My bay 1 converter at 1500-2000 RPM sounds like some one is kicking a tin can down the road. Nissan mechanic thinks that my converter has fallen apart internally. Yet it does not give me any error codes. I don't drive my car right now cause it has P0300. I am trying to figure out the reason for random misfire before I address Bay 1 converter.

disallow wrote:Hi SMJ,

I've had a nagging P0430 code for the last 6 months or so.

In your experience, can this be caused by a bad secondary O2 sensor? Only reason I ask is that when I check the voltages at 2000rpm, the voltage on the rear O2 sensor on the one side is all over the place, from 0.1v to 0.9v, but the Front sensor seems to be fine, at a stable 0.6v.

I've never changed the rear sensors, but did the front sensors about 30k miles ago.

Everything else seems normal. Performance, exhaust smell/appearance, fuel economy, etc. But I've also heard the horror stories of degraded catalysts getting sucked into the exhaust valves... Would rather avoid that...

t

It's hard to determine catalyst efficiency by scan tool testing as there are a lot of variables. The general logic of catalyst efficiency is the observance of the rich-lean cycling frequency of the oxygen sensors; the rear sensor should have about half the cycling frequency of the front. If the front sensor is an air/fuel sensor, rather than an oxygen sensor, it makes it tougher being that air/fuel sensors run in a much narrower band, as I stated in the previous post. There are also a number of other values that the ECM looks at during it's determination of how efficient the converters are working, which is why it's a matter best left to the ECM. Usually if there is a problem with the sensors, the ECM will see it and trigger a sensor failure code and/or a catalyst efficiency code; in that particular case, one would ignore the catalyst code, address the sensor code, erase all codes and then see if the catalyst code re-sets. Same would go for any other code (such as a mass air sensor code) set with a catalyst efficiency code. Air/fuel sensors can be very tricky to determine if they are operating properly if you are graphing them in the same scale as you would an oxygen sensor; if you do, it often looks like the sensor is doing nothing or very little, whereas an oxygen sensor can range up to 1.1v and as low as 0v. Without other codes or exhaust leaks, it is usually the upstream catalytic converter that is at fault when a P0420/P0430 DTC is set.

smj999smj wrote:
It's hard to determine catalyst efficiency by scan tool testing as there are a lot of variables. The general logic of catalyst efficiency is the observance of the rich-lean cycling frequency of the oxygen sensors; the rear sensor should have about half the cycling frequency of the front. If the front sensor is an air/fuel sensor, rather than an oxygen sensor, it makes it tougher being that air/fuel sensors run in a much narrower band, as I stated in the previous post. There are also a number of other values that the ECM looks at during it's determination of how efficient the converters are working, which is why it's a matter best left to the ECM. Usually if there is a problem with the sensors, the ECM will see it and trigger a sensor failure code and/or a catalyst efficiency code; in that particular case, one would ignore the catalyst code, address the sensor code, erase all codes and then see if the catalyst code re-sets. Same would go for any other code (such as a mass air sensor code) set with a catalyst efficiency code. Air/fuel sensors can be very tricky to determine if they are operating properly if you are graphing them in the same scale as you would an oxygen sensor; if you do, it often looks like the sensor is doing nothing or very little, whereas an oxygen sensor can range up to 1.1v and as low as 0v. Without other codes or exhaust leaks, it is usually the upstream catalytic converter that is at fault when a P0420/P0430 DTC is set.

Hi smj999smj,

What is your opinion on the situation when bay 1 a/f sensor operating around 0.3 volt and bay 2 a/f sensor operating around 0.6 volts? Shouldn't they be similar? Thanks for your answer!

Well, you don't mention whether this "average voltage" is taken at idle, or at a specific RPM. In theory, both sides should be close. If this average is taken while cruising down a flat highway at a steady RPM, the 300 millivolts value sounds a bit low. FYI, Nissan ECMs have an O2 sensor fail-safe of 333 millivolts for when the O2 sensor circuit opens; this gives it something to work off that is neither too rich nor too lean of a value for when something happens to that sensor's circuit. This will, or should, always trigger and oxygen sensor (or A/F sensor) trouble code. Sensors can get dirty; it's a bit of a pain to get to the front sensors on an R51, but you could remove the sensor when it's cold and spray the element down with electrical contact cleaner. If the sensor signal is steady at .3V and shows no movement, I would check the circuit and if it proves good, replace the sensor.