# Bank 1 runs "lean" after upstream oxygen sensor replacement **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** nissan, pathfinder\ **Created:** [December 11, 2016, 1:38am UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060 "2016-12-11T01:38:11Z")\ **Posts on this page:** 20\ **Page:** 6
**Author:** ![Stevebone](https://avatars.discourse-cdn.com/v4/letter/s/47e85d/32.png) [@Stevebone](https://community.cartalk.com/u/Stevebone)\ **Post date:** [December 26, 2016, 11:58pm UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/101 "2016-12-26T23:58:02Z")
That is the guy in the link I posted ---
**Author:** ![Stevebone](https://avatars.discourse-cdn.com/v4/letter/s/47e85d/32.png) [@Stevebone](https://community.cartalk.com/u/Stevebone)\ **Post date:** [December 27, 2016, 12:16am UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/102 "2016-12-27T00:16:54Z")
Another one with B1 @ 0.3V and B2 @ 0.6V: Jinxed Joined: 29 Jun 2012 Posts: 5 Location: Ontario,Canada PostPosted: Tue Jul 03, 2012 4:29 pm Post subject: Reply with quote So it turns out I did right down the wrong code but it was P1271. Still indicated air fuel ratio sensor 1. Took a picture of the O2 sensor readings while traveling 90 kmh but can’t seem to attach it using my iPhone. Here are the readings: O2B1S1 .305 O2B1S2 .930 O2B2S1 .610 O2B2S2 .650 O2B1S1 never fluctuated at all just stayed at .305. O2B1S2 usually ran around .930 but would occasionally drop below .150 I’m going to order the front a/f sensor and change it hopefully this week. I will post results.[/img] * * * 2005 Pathfinder SE Off Road ---
**Author:** ![Stevebone](https://avatars.discourse-cdn.com/v4/letter/s/47e85d/32.png) [@Stevebone](https://community.cartalk.com/u/Stevebone)\ **Post date:** [December 27, 2016, 6:39am UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/103 "2016-12-27T06:39:58Z")
Hello Well I just disconnected two fuel injectors to try and coax the 1500 RPM down to attempt to temporarily trick the ECM into a relearn to fix P0507, (got that from a blog post by a Nissan Tech), sounds kinda not right, I thought I would give it a try anyway. I also put my hand inside the intake just fwd of the MAF to restrict airflow to get the RPM even lower, the engine would not stall, I then jammed a big towel into the intake and completely blocked it, the engine still runs at 500 RPM with a fully blocked intake and with two fuel injectors electrically disconnected. I had done this same thing a few days ago but without any fuel injectors disconnected and it always stalled out when the intake got about 75% blocked, but with the two cylinders not working the engine is now able to run from an unknown vacuum leak with a fully blocked intake. I did a propane test and spray water test while the engine was running in this condition, noticed a slight RPM change with the water being sprayed between the intake manifold collector and the intake. I will have to go back and research this: I had read something somewhere about how this engine has as part of its emissions a process that recirculates some of the exhaust back though the intake? Maybe this is why the engine can still run in this condition? Can it run by sucking air back up the exhaust in this limited no load operating condition? My first assumption would be no, but the more I read about these new engines, I cannot assume anything until I find a reliable source to set me straight. I will try and hunt the exhaust process info down, I hope I am wrong and it is not the case. Then I could have actually found a diagnostic starting point, a vacuum leak that effects both banks? Maybe, because I disconnected two injectors on B2, I will redo the running engine condition and disconnect the 3rd fuel injector on B2 to notice any difference. Then do the same to B1. I just tried to repeat the same condition, every time I started to fully insert the towel into the intake pipe it would stall, I drove the PF around again after reconnecting all fuel injectors, just as I did the first time, same result: a stall. I disconnected that 3rd fuel injector after doing the towel blockage test and there was an obvious change. I did the dollar test to the tail pipe to see if it was sucking air: it was not. Maybe the water I poured on the intake stopped up the vacuum leak, especially if it caused the intake gasket seal to close up temporarily, will go out and try to replicate it again in the AM. ---
**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\ **Post date:** [December 27, 2016, 2:02pm UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/104 "2016-12-27T14:02:19Z")
I see you really go into an extreme trying to diagnose it. I might assume that towel is not exactly air-tight, so engine will continue to suck air through it. You might want to put a piece of plastic into that towel to prevent it from filtering air through. Throttle body would have hose connected for fuel tank vapor purge IMHO, this would be another source for “leak”. ---
**Author:** ![Stevebone](https://avatars.discourse-cdn.com/v4/letter/s/47e85d/32.png) [@Stevebone](https://community.cartalk.com/u/Stevebone)\ **Post date:** [December 27, 2016, 10:06pm UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/105 "2016-12-27T22:06:17Z")
You are right about the air getting past the towel and through the vapor hose. Well I can either go to dealer and have them hook it up to see if they can fix P0507 with the Nissan Scanner at $100+ and even then they may tell me I need a new TB, or R&R TB with a rebuilt one for $110 after my mil discount from AZone. I am going with the R&R TB. For the P0430 I have a O2 spacer I will install so I might be able to get it to pass smog and then later on R&R B2 fwd Cat. I still wanted to do a little more trouble shooting to see if there was a cause for the CAT failure, or if it just wore out after 178K? I had already R&R B1 CAT @ 152K due to thermal shock when a coolant tube on the pax side fire wall to the heater system broke and leaked all over it while my son was driving @ 70 mph, 200 degree coolant showers 600+ degree CAT = super steam bath. Did you do the ECM R&R? ---
**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\ **Post date:** [December 27, 2016, 10:09pm UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/106 "2016-12-27T22:09:03Z")
left for vacation, so do not know if they sent it back yet I hope to get it soon and will post results ---
**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\ **Post date:** [December 27, 2016, 10:12pm UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/107 "2016-12-27T22:12:25Z")
on R&R on your TB: I hope it helps in your case, as your high RPM situation should have an explanation in some leak, and likely not a small one R&R I did so far on my car only made it to run better and smoother, and considering I want to keep this car for quite some time, it is not in vain ---
**Author:** ![Stevebone](https://avatars.discourse-cdn.com/v4/letter/s/47e85d/32.png) [@Stevebone](https://community.cartalk.com/u/Stevebone)\ **Post date:** [December 27, 2016, 10:13pm UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/108 "2016-12-27T22:13:13Z")
My over doing it with the diagnostics is due to I enjoy trying to figure it out and my limited funds to spend on parts. Have a good trip ---
**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\ **Post date:** [December 27, 2016, 10:17pm UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/109 "2016-12-27T22:17:01Z")
in my case from “enjoying / educational”, it moved heavily into the latter one already blew the budget I was allocating for this project… still need to get it going ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [December 28, 2016, 2:53am UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/110 "2016-12-28T02:53:37Z")
There’s one air path into the engine you may not be blocking off, the pcv path. No sure how your PF is configured, but on most pcv systems there’s usually a hose from the air cleaner area providing clean air to one of the valve covers. From there it goes down into the crankcase, then back up to the other valve cover, then through the pcv valve and into the intake manifold. The pcv valve isn’t supposed to allow much air to flow in that path at idle though. Hard to believe that path would allow 500 rpm. It’s usually possible to temporarily block that path, sometimes that’s a useful test. The exhaust gas re circulation function isn’t done w/ an air path. Only exhaust gasses are re-routed to the intake manifold. And none at idle if it is working correctly. That path gets activated on rapid accelerations and heavy engine load conditions like steep uphills. There’s very little O2 in that path. However, if the egr gasses flow into the intake manifold at the wrong engine operating conditions (such as idle) it will definitely cause the engine to bog or even stall since it displaces the available O2. ---
**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\ **Post date:** [December 28, 2016, 3:48am UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/111 "2016-12-28T03:48:04Z")
PCV valve hose is connected to the air intake behind the throttle body, on the passenger side this one is very easy to test by disconnecting and blocking one and another side with your finger another PCV hose is connecting left and right banks and is located to the front of the engine, under the pipe connecting injector fuel rails: quite hard to get into, but easy to test for leaks once removed ---
**Author:** ![Stevebone](https://avatars.discourse-cdn.com/v4/letter/s/47e85d/32.png) [@Stevebone](https://community.cartalk.com/u/Stevebone)\ **Post date:** [December 28, 2016, 3:50am UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/112 "2016-12-28T03:50:59Z")
Thanks for the info ---
**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\ **Post date:** [December 28, 2016, 4:16am UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/113 "2016-12-28T04:16:29Z")
hey, if you suspect vacuum leaks, do you by any chance observe any oil seeping from under the valve covers? if yes, this is where vacuum from PCV hoses goes, and if oil sips badly, I might imagine to have some vacuum leak there only a wild guess on my side ---
**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\ **Post date:** [December 28, 2016, 4:19am UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/114 "2016-12-28T04:19:23Z")
BTW, I indeed had a small leak between the aluminum intake and heads: not much, but once I replaced metallic gaskets, it definitely was a visible improvement if ever go this route, pay attention that gasket manufacturers suggest no additional silicone to be placed there: this joint is supposed to allow for thermal expansion/contraction and should be “dry” ---
**Author:** ![Stevebone](https://avatars.discourse-cdn.com/v4/letter/s/47e85d/32.png) [@Stevebone](https://community.cartalk.com/u/Stevebone)\ **Post date:** [December 28, 2016, 4:41am UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/115 "2016-12-28T04:41:13Z")
No oil leaks, or for that matter vacuum leaks, I only thought I had a vacuum leak because of my assumption from the towel in the intake. The high RPM is from me cleaning the TB, thus the Nissan Service Bulletin says you have to take it in to have it fixed by a tech using the Nissan Scanner. But I also manually moved the butterfly valve, some blog post say doing this messes up the IAC gears, and only fix is to R&R TB. ---
**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\ **Post date:** [December 28, 2016, 2:07pm UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/116 "2016-12-28T14:07:30Z")
[nissanhelp.com](http://nissanhelp.com) has procedures published for idle speed re-learning and for A/F mixture ration re-learning you can do on your own, just go to their section on PF ---
**Author:** ![Stevebone](https://avatars.discourse-cdn.com/v4/letter/s/47e85d/32.png) [@Stevebone](https://community.cartalk.com/u/Stevebone)\ **Post date:** [December 28, 2016, 7:25pm UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/117 "2016-12-28T19:25:13Z")
I have done that over a dozen times, no go ---
**Author:** ![Stevebone](https://avatars.discourse-cdn.com/v4/letter/s/47e85d/32.png) [@Stevebone](https://community.cartalk.com/u/Stevebone)\ **Post date:** [January 1, 2017, 7:20pm UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/118 "2017-01-01T19:20:44Z")
Solved P0507 code (high idle) by R&R TB and relearn. P0430 is back (bad CAT B2) will attempt to pass smog (registration due) by using O2 spacer until I can get the CAT R&R next month. MPG is slowly going back up, now @ 12 mpg vs. the 8 it was getting when it had the 1500 RPM idle, PF runs great otherwise. Although it cost me $140 for rebuilt TB the best thing about getting it fixed was able to avoid taking it to the dealer or a non dealer shop. ---
**Author:** ![db4690](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/db4690/32/2583_2.png) [@db4690](https://community.cartalk.com/u/db4690)\ **Post date:** [January 1, 2017, 7:40pm UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/119 "2017-01-01T19:40:01Z")
Congratulations on getting the throttle body fixed ---
**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\ **Post date:** [January 1, 2017, 7:44pm UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/120 "2017-01-01T19:44:46Z")
congrats on getting your idle under control ! replacing cat on your own is a pain as it is [surprisingly] small space to work there and I was not able to ever remove heatshield (at least on bank 1) and needed to “dance around it” hint for you if you go this direction: all bolts on heatshield WILL break, so be prepared to weld bolts on boken ones and to use nuts after that, but even after that heatshield will be impossibel to remove even after removing some components around, you will have to simply push it aside dealer tech-manual suggests removing engine from the car to replace cat, which was absolute no-go to me cost-wise, so I had to improvise looks like now we are getting into the same boat, only on another bank side in your case my R&R techs called Friday and said my ECM is 100% good and does not require any repairs, so I’m back to square one ☹ reviewing suggestions from [http://www.brakeandfrontend.com/](http://www.brakeandfrontend.com/), their expert suggests that many “imports” use both upstream and downstream sensors when making decision on A/F ratio, so as a next step I’m to put new downstream sensors, resulting in all 4 oxygen sensors to be new, hopefully it helps another “strange idea” on A/F mix uneveness I have is correlation between me replacing spark plugs and appearing of this problem. I should confess I used double-palinum AutoLight’s, not OEM NGK’s, so I’m replacing these too to close this avenue as well, but only after replacing sensors all parts come in mail only late this week, so likely I will do next update after that [Previous page](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060.md?page=5) [Next page](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060.md?page=7)