Bank 1 runs "lean" after upstream oxygen sensor replacement

Maintenance/Repairs
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O2 sensors aren’t a common failure item. I forget what year your Nissan is. But I replaced an O2 sensor on my 20+ year old Corolla, no difference. The new sensor worked exactly the same as the old one. It sounds from your comments however like your new sensor seems to work a little better, at least more responsive. I purchased a Denso sensor for my Corolla, which is the oem version. Be aware that o2 sensors have to be clean on the part that is outside the engine. There’s an air channel from the inside part to the outside part that needs to be free to breath for it to work accurately. Sometimes they get coated w/oil on the outside the engine part, near where the connector is, and that air channel gets plugged up.

Forget if you’ve already mentioned it, but have you had a fuel trim measurement done?

1 Like
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Hiya,

Are you still getting PA200, or any other code? How is your MPG and Fuel Trim? How does your PF run at WOT?

I still have high idle with only the PO507, I am going to smoke test my 05 PF again, if that cks good, I will take it to shop to have Nissan Service Bulletin procedure (that I had mentioned before) completed.

Yes “The Tell Tale Heart” is a good story, I have not read it in decades, will read soon again now that its on my mind per your suggestion.

The only way to get a trusted AF Sensor Volt reading is to take it to Nissan and have it put on their Consult II diagnostic computer. The official PF MX book states both AF Sensors normally work around 1.5 Volts. So not only is your B1 at 0.3V off the mark so is your B2 at 0.6V. My after market scanner gives me the same reading as yours, B1 at 0.3V and B2 at 0.6V, This highly suggests our AF Sensors are operating normally and its these after market scanners that are limited on how to read the data because Nissan does not share its proprietary software coding.

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I just recalled, there may be another way to check the AF Sensor Volts, with a multimeter, there are several youtube posts on how to do it.

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fyi, one common reason for high idle rpm is the engine isn’t reaching its designed operating temperature, usually due to a leaking thermostat. Good idea to check on that before assuming it is something more complicated.

1 Like
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Still getting P2A00, but after getting an OEM sensor, it threw it MUCH FASTER

I decided to recheck all the wiring, and I have officially confirmed that all the wires are in order, resistance is under 1 ohm in all connections, sensors get power.

Given all the facts, the only part I did not replace yet is ECM itself.

eBay has several stores offering “Repair and Return” service for ECM, ranging between 150 and 300

Not sure if this is a good direction to go next

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I’ve decided to swap left/right sensors, and what I found is that Bank 2 has not carbon fouling at all, while Bank 1 is covered with carbon powder a little bit, so presumably while it reports lean, it actually runs reach.

Short-term trims reported are not appreciably different (less than 0.5% of difference) between banks, and they are around zero anyway, so not much deviating from the preprogrammed values.

I wonder how to check if system tries entering closed loop, on each bank individually?

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Just found this:
P2A00 NISSAN - Air Fuel Ratio Sensor Circuit Range/Performance Bank 1 Sensor 1 6 | Add Comment Possible causes - Air Fuel Ratio (A/F) Sensor Bank 1 Sensor 1 - Air Fuel Ratio (A/F) Sensor Bank 1 Sensor 1 harness is open or shorted - Air Fuel Ratio (A/F) Sensor Bank 1 Sensor 1 circuit poor electrical connection - Fuel pressure - Fuel injector - Intake air leaks What does this mean? Tech notes If the P2A00 code is set after a sensor is replaced, check for exhaust leaks and perform the mixture ratio self-learning procedure. What does this mean? When is the code detected? The output voltage computed by ECM from the A/F sensor 1 signal is shifted to the lean side for a specified period. Possible symptoms - Engine Light ON (or Service Engine Soon Warning Light) P2a00 Nissan Description The Air Fuel Ratio (A/F) sensor is a planar dual-cell limit current sensor. The sensor element of the A/F sensor is the combination of a Nernst concentration cell (sensor cell) with an oxygen-pump cell, which transports ions. It has a heater in the element. The sensor is capable of precise measurement λ= 1, but also in the lean and rich range. Together with its control electronics, the sensor outputs a clear, continuous signal throughout a wide range (0.7 < λ < air). The exhaust gas components diffuse through the diffusion gap at the electrode of the oxygen pump and Nernst concentration cell, where they are brought to thermodynamic balance. An electronic circuit controls the pump current through the oxygen pump cell so that the composition of the exhaust gas in the diffusion gap remains constant at λ = 1. Therefore, the A/F sensor is able to indicate air/fuel ratio by this pumping of current. In addition, a heater is integrated in the sensor to ensure the required operating temperature of 700 - 800°C (1,292 - 1,472°F).

Read more: http://www.autocodes.com/p2a00_nissan.html

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I will check it, Thanks

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1998-2012 Nissan Pathfinder Clear Mixture Ratio Self-Learning Control Data

Models:
1998 Nissan Pathfinder
1999 Nissan Pathfinder
2000 Nissan Pathfinder
2001 Nissan Pathfinder
2002 Nissan Pathfinder
2003 Nissan Pathfinder
2004 Nissan Pathfinder
2005 Nissan Pathfinder
2006 Nissan Pathfinder
2007 Nissan Pathfinder
2008 Nissan Pathfinder
2009 Nissan Pathfinder
2010 Nissan Pathfinder
2011 Nissan Pathfinder
2012 Nissan Pathfinder
Mixture Ratio Self-Learning Control

The mixture ratio feedback control system monitors the mixture ratio signal transmitted from air fuel ratio (A/F) sensor 1. This feedback signal is then sent to the Engine Control Module (ECM). The ECM controls the basic mixture ratio as close to the theoretical mixture ratio as possible. However, the basic mixture ratio is not necessarily controlled as originally designed. Both manufacturing differences (i.e., mass air flow sensor hot wire) and characteristic changes during operation (i.e., fuel injector clogging) directly affect mixture ratio.

Accordingly, the difference between the basic and theoretical mixture ratios is monitored in this system. This is then computed in terms of “injection pulse duration” to automatically compensate for the difference between the two ratios.

Fuel trim refers to the feedback compensation value compared against the basic injection duration. Fuel trim includes short term fuel trim and long term fuel trim.

Short term fuel trim is the short-term fuel compensation used to maintain the mixture ratio at its theoretical value. The signal from air fuel ratio (A/F) sensor 1 indicates whether the mixture ratio is RICH or LEAN compared to the theoretical value. The signal then triggers a reduction in fuel volume if the mixture ratio is rich, and an increase in fuel volume if it is lean.

Long term fuel trim is overall fuel compensation carried out long-term to compensate for continual deviation of the short term fuel trim from the central value. Such deviation will occur due to individual engine differences, wear over time and changes in the usage environment.

Instructions

1Start engine and warm it up to normal operating temperature.
2Turn ignition switch OFF.
3Disconnect mass air flow sensor harness connector, and restart and run engine for at least 3 seconds at idle speed.
4Stop engine and reconnect mass air flow sensor harness connector.
5Make sure Detected Trouble Code (DTC) P0102 is displayed.
6Erase the DTC memory. (This could be done by disconnecting the car battery for 30-45 min or with a scanner)
7Make sure no codes are stored in the ECM.
8Run engine for at least 10 minutes at idle speed.

Read more: http://nissanhelp.com/diy/pathfinder/projects/nissan_pathfinder_clear_self_learning.php#ixzz4TBxjjol8

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CONSULT-II Reference Value in Data Monitor Mode UBS00KE3
Specification data are reference values.
On Board Diagnosis Logic UBS00KE4
To judge the malfunction, the diagnosis checks that the A/F signal computed by ECM from the air fuel ratio (A/
F) sensor 1 signal is not inordinately low.
DTC Confirmation Procedure UBS00KE5
NOTE:
If DTC Confirmation Procedure has been previously conducted, always turn ignition switch OFF and wait at
least 10 seconds before conducting the next test.
TESTING CONDITION:
Before performing the following procedure, confirm that battery voltage is more than 11V at idle.
WITH CONSULT-II

  1. Start engine and warm it up to normal operating temperature.
  2. Select “A/F SEN1 (B1)” or “A/F SEN1 (B2)” in “DATA MONITOR” mode with CONSULT-II.
    SEF579Z
    SEF580Z
    MONITOR ITEM CONDITION SPECIFICATION
    A/F SEN1 (B1)
    A/F SEN1 (B2) Engine: After warming up
    Maintaining engine speed at
    2,000 rpm
    Fluctuates around 1.5V
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at this point I’m to get my friend’s truck for my vacation trip :frowning:

while I’m out, ECM goes for “repair and return”

getting two new OEM upstream sensors ready to make sure when I put everything back, I have all components controlling closed loop in confirmed good condition

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I have been trying to teach myself about AF Sensors. I learned That depending on the Scanner it will set its own unique default volt for AFS, Nissan Official scanner is 1.5V @ 2000 rpm, I saw Snap-on Scanner set AFS for Toyota @ 3.3V. My Scanner (blue driver) is either closer to .3V B1 or .6V B2, same as yours, it is possible that B1 and B2 have different default volts? Or either one is lean or one is rich?
AFS use very low current to communicate with the ECM, the ECM then converts the current sent to it into a non real volt signal that I guess makes it easier to interpret on a scanner?
When AFS is operating at 0.00MA (0 current) the bank is working at peak performance of an Air to Fuel ratio of 14.7 to 1.
If this ratio is off balance the ECM commands more or less fuel injector open time to keep the AFS as close to 0.00MA as possible.
If there is a rich mixture there will be a neg current flow, lean a pos, the current is then converted by the ECM to a voltage PID.
And depending on the scanner those PID volts can be different, one scanner has the 0.00MA set as 0.5V, and when V are 0.6 to 0.9 that is lean. At 0.4 to 0.1 that’s rich. I believe my scanner is set to these V readings. Where the Snap-on mentioned before 0.00MA current is 3.3V.
The strange thing is the AFS and O2 S can only read oxygen, so when these sensors detect a high level of oxygen (AFS reads in a scanner as a lean condition), the ECM tells the fuel injectors to open even longer sending even more fuel to that bank, result is a very rich bank that the ECM thinks is not getting enough fuel. This can be confirmed by LTFT and STFT.
You can feed propane into the intake TB and the AFS Volts should go down and the FT should go rich as in 0% or a -%. Turn off the propane and AFS volts should go up and FT % should + increase both temporally.
This would explain why a lean condition would match up with an increase in MPG.
I will take a day or two off, and then do more reserch, my PF has 175K, I would like to keep it going for another 100K plus.

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in theory, REAL voltage can not be different: it is determined purely by chemistry, not by any electronics

you’ve got a good point that ECM “fudges” readings, I’m quite sure it does, as no way PIDxxx values I observe are real: both range and base points are at least 3-5 times off from what OBD PIDs are reporting

fouled AFS I observed is indeed a consequence of ECM pumping more and more fuel to compensate for what it thinks to be a lean condition, resulting in rich one

I’ve finally removed my ECM (pain!) and will send it for testing/repairs: http://www.ebay.com/itm/Nissan-Pathfinder-ECM-ECU-PCM-Engine-Computer-Repair-Return-Nissan-ECU-Repair-/321701420536

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we are talking PIDs 0101 and 0105

as you see, their range is fudged by some “formula”

so far I can not figure out how to arrive to “real voltage” from what PID reports (0.3 / 0.6)

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Thanks for the info and links, I just found this:

Recall for 2006 Nissan Pathfinder

Recall Announced
OCTOBER 28 2010
NHTSA Reference
#10V517000
Number Affected
747,480
Summary: Nissan is recalling certain model year 2004-2006 armada, titan, infiniti QX56 and model year 2005-2006 frontier, Pathfinder and xterra vehicles. The intelligent power distribution module (ipdm) assembly contains an engine control module (ECM) relay that has a diode for electrical current noise reduction. The ECM relay may allow silicon vapor to form and, over time, the silicon evaporates from the diode molding which causes silicon oxide to develop on the ECM relay contact due to arcing.

Consequence: This could cause engine stalling increasing the risk of a crash.

Fix: Dealers will replace the ECM relay inside the ipdm assembly. This service will be performed free of charge. The safety recall began on December 6, 2010. Owners may contact Nissan at 1-800-647-7261.

For detailed information & supporting documents, see the official NHTSA page concerning recall #10V517000 »

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None of you guys have described a stalling problem

No offense, but I’m not sure this recall will actually fix your problem

It might, but I wouldn’t be surprised if after the recall, the same codes keep coming back

For that matter, how do you the recall hasn’t yet been performed . . . it’s from 6 years ago, after all

call the phone number and give them your vin number . . . they should be able to tell you if the recall has been completed or not

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Could there be a problem with the VVT? If the VVT actuator isn’t fully returning to the idle position wouldn’t a lean condition be the result? I am not at all familiar with the VVT on the OP’s Pathfinder so other than throw the idea out of the box I’m useless. I found nothing worthwhile in a quick search of the issue.

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On the engine diagram, I found valves to be directly pushed from the shaft, no any VVT, very low-tech

79

Re: air flow sensors

It seems like a problematic air flow sensor in a 2-bank engine would result in a rich or lean condition in both banks, rather than just one. Presuming this engine is configure w/just one airflow sensor which services the common air nflow for both banks.

fyi, dirty air flow sensors can indeed cause lean codes. The way they work usually is they power up an electrical circuit current flow which heats up a wire located in the center of the intake air stream to a certain temperature well above ambient. A temperature feedback circuit adjusts the current as necessary to maintain the wire at the designed temperature at all times. During periods of increasing airflow more current is needed to maintain that temperature. B/c the increasing airflow otherwise would cool the wire down. So the amount of current flow is proportional (in some known way) to the actual airflow.

If the wire gets coated with dirt or oil, it’s like putting a coat on the wire. The wire, thermally insulated by the dirt, will stay warmer for a given air flow. So a contaminated air flow sensor will not report the actual air flow; instead – b/c less current is required to keep the wire at that temperature – it will report an air flow less than what is actually occurring. This will confuse the ECM, and it may then post a lean code. But like I say above, it seems like it would post the lean code for both banks then.

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I find it curious that you originally had a B1 PO420 code with B1 AF Sensor with a 0.3V and a B2 with a 0.6V. While I have a B2 PO430 code with the exact same two AF Sensor Volt readings (B1 0.3V, B2 0.6V)? You could assume the Voltage rates would/should be reversed? But not so!

Just did a propane test, AF and O2 sensors, as well as STFT and LTFT data was collected. Although the B1 and B2 AF Sensors starting baseline voltage is different, during the test the rate of change for both sensors was almost identical, when B1 would go down to 0.25V, B2 would go down to 0.55V, the same 0.05V drop.

While using my scanner @ 1500 RPM no load, no propane I did find a really high switching rate on B2 O2 Sensor compared to B1 O2 Sensor.
Also found FT difference when both LTFT and STFT where added together, B1 was avg around 3% while B2 was avg -12% (rich). The high switch rate highly indicates B2 Cat needs to be R&R. Not sure about the FT?

Also why do I have a high mpg rate?

So is this bad Cat the cause to why the FT on B2 is an avg of -12% and is it also the cause of my high mpg rate, or is the -12% FT the cause of the Cat going bad and is the result of one or more other non-Cat components malfunctioning? Time for more research.

During propane test I noticed both AF Sensors voltage would drop an equal amount for a few seconds then return to the normal individual voltage rates even with propane still on, this suggested to me the ECM, AF and O2 sensors are all operating in good order to keep the engine as close as possible to the 14.7 to 1 ratio. So the ECM cut fuel injector pulse rate during propane injection based on the input data from both of the banks AF and O2 sensors. Both AF Sensor Volts decreased by the same voltage amount before returning back to normal individual rate, this indicates to me that both banks are operating the same, if one of the banks was having misfires due to a bad coil, plug or fuel injector, these voltage drops would be different? Also this would rule out a specific Bank only intake leak or exhaust leak? Am I correct in this analysis? If both AF Sensors closely mirror each others actions (except for our unknown reason for the baseline 0.3V and 0.6V difference) would that not indicate the banks are working the same, and if one bank had a specific problem the AF Sensor voltage fluctuations during RPM changes would be way different even if it was for a very short time until the ECM changed the fuel injection pulse rate on the effected bank?

I can understand the O2 Sensor having way different readings because of a Cat being clogged up, being inefficient compared to the good bank. But the AF Sensors should read the same unless there is a specific problem with one of the AF Sensors or a problem on that specific bank that would/should cause another code (like a misfire code) besides the PO420/PO430 to come on? You would think after this diagnostic and if no other problems are found and no other codes set you could assume it is only the Cat that has gone bad and nothing else?

I did notice a lag on B1 O2 Sensor compared to B2 O2, but it is B2 with the Cat code, so is B1 slow or is B2 reacting faster because the Cat is not working. I believe it is because B2 Cat is not working (like it is not even there, that means it is not currently clogged I assume). Because we have AF sensors we cannot compare a specific banks O2 upstream to an O2 downstream, but we can compare B1 O2 to B2 O2.

I did read when certain codes set it stops the ECM from further self diagnostics until that code is fixed, I believe the case I read about was an AF Sensor code and thus no other emissions self test would be completed by the ECM until that code was no longer detected. That makes sense, because without a functional AF Sensor the ECM would not get the data to know the Cat has also gone bad, but its also why you hear about people feeling they are getting ripped off because they pay to have one code fixed then soon after a new different code pops up that is usually more expensive to fix.

I have done multiple tests to look for intake leaks, by using scanner, water, smoke, propane, but the most reliable test (I believe) was done with a vacuum gauge. You can use a vacuum gauge to test intake, exhaust, valves, rings, head gasket, and improper idle mixture. All tests were good.

I still have my high idle code PO507, in park it idles @ 1500 RPM.
After checking for intake leaks and the PCV the next step is to take it to a shop to have the NSB done with a high end diagnostic machine, if that’s a no-go, depending on the data found, maybe next step a TB R&R?

If and when I make to a shop I will check out the AF Sensor Volt readings on the shop’s machine tester.

It would be great if we had someone else in the forum with a 05/06 PF and an after market scanner to tell us their AF Sensor readings. If 3 PF’s have the the same B1 0.3V and B2 0.6V reading, I would assume that would prove that these are the normal baseline volt rates assigned to the sensors.

So the ECM has no control over the amount of oxygen volume entering the engine to include a specific bank, it only detects the ratio of oxygen to fuel. The ECM does have control over how much fuel will be used through the injectors by adjusting pulse length rate in an attempt to align with the oxygen to keep the ratio of 1 pound of fuel to 14.7 pounds of “oxygen” (or is it air?)

The ECM so far as I have read only reports STFT and LTFT, it does not make any fuel injector pulse rate changes based off these two sets of collected data.

What about the Throttle Body, is the butterfly valve angle degree only based off peddle depression (or cruse control setting), from what I understand this is mostly how it works? In other words the ECM makes no butterfly angle adjustments to attempt to control the 1 to 14.7 ratio. Not sure what happens during limp mode, how does the ECM control the engine components to put it into limp mode to prevent the engine from going above 2500 RPM or above of 2nd gear? I suspect it would be by limiting fuel injector pulses and or preventing the transmission from working above 2nd gear? The ECM makes no fuel injector pulse rate adjustments when a misfire code becomes active due to any component malfunction, the only adjustment it makes is based off the AF and O2 sensors or when it detects a performance issue that will cause it to go into limp mode, I assume that would happen if the 1 to 14.7 ratio goes over a predetermined set limit, and or if the transmission started to fail to the point it might seize up?

So if one or more components are not functioning correctly but have not misbehaved bad enough to set there own code (if there even is a code to be set) that could cause a code like PO430 or PO507 to occur, and now its time to diagnose, or just start changing parts from easy/cheap to hard/expensive, or let the shop fix it.

But I like working on cars, and I plan on keeping my PF for as long as practical, I am going to try to accurately diagnose through research, and getting advice (like this blog). I bought this PF new, and now its starting to have issues that require more knowledge on how to trouble shoot and repair correctly, my biggest road block to this is not having advanced diagnostic equipment and the expertise to use it. I did hear about a do-it-yourself repair place here in Vegas, maybe they have a high end diagnostic with pay as you go tech. I just looked them up, closed now, they have a LAUNCH SCAN PAD, a lot more ability then my $99.00 blue driver. Cool for $50 an hr a tech will help you.

I read on the Nissan forum several ways to possible fix a PO507, so far I have tried them all several times, no-go, still one more to do, one person claimed they fixed PO507 by re-cleaning TB again this time off engine and lubed up butterfly rod, did relearn, I will give it a try. I am so tempted to take TB apart by drilling IAC cover rivets out, I just might do that if it comes down to the only option left is to R&R it, it will be worth the core charge to me to be able to tinker with it in the very remote chance I could repair the IAC guts.

Sorry for the long post, but I mainly write this out to help myself think the problem through, and to get feed back where I am wrong.

Hey good luck with the ECM repair, your info and that of the others along with the many suggestions on this blog has helped me in my decision making on how I should work my code problems.

Thanks everyone for the help, will update.

I look forward to reading the cure that resolved your code, its like a detective story with many plot twists, a surprise ending is coming.

Stevebone