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post #1 of 19 (permalink) Old 05-05-2019, 08:52 PM Thread Starter
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P0171 trouble code

Hey guys, I'm usually pretty good at figuring these things out but I figure someone on here might have had the same issue and can help speed up the repair process.


So TC P0171 is bank 1 lean


I love my 2004 Titan and all repairs before this have been straightforward, but this one is grinding my gears.



I swapped the up stream O2 sensors from side to side and nothing changed.

I replaced PCV valves

I looked for vacuum leaks and nothing, I even took the intake manifold off and replaced the gaskets to no avail.

I don't hear or remotely notice any exhaust manifold leaks, not sure if an extremely small one can cause my issue.

I checked o2 harness wiring/voltages and everything checks out

balance tested bank 1 and each cylinder makes a difference in idle whether I remove ignition coil connector or injector connector

Truck starts right up fast, idles good, and has good power/torque, but the exhaust does not smell correct to me.

Closed loop o2 data is bank 1 hangs around .300 while bank 2 is at .600, fuel trim for bank 1 is +25%


kinda stumped on this one. I am not sure if the VVT can do this and NOT set a code? Anyone run into a tough performance issue like this before with their Titan where one Bank is lean and most common repairs or avenues have not rectified the problem?

Last edited by Jay Moore; 05-05-2019 at 08:56 PM.
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post #2 of 19 (permalink) Old 05-06-2019, 04:27 AM
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My guess based on everything you've checked is one of two things. Either you have an air leak between the MAF and the cylinders (either air intake connections or vacuum leak) or you have an exhaust leak. I know you said you checked for a vacuum leak, but unless you smoked the system to check everywhere, that's still a good possibility. These kinds of things are a real pain to doagnose.
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post #3 of 19 (permalink) Old 05-06-2019, 05:58 AM
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Re: P0171 trouble code

can you check the long term trims on the motor??? do you have a scan tool???

anything over 12% and it will code. you need to have the intake system checked leaks. there is some false air coming in and it is causing this issue. if it were fuel pressure, pcv or mass air flow, it would effect both banks.

Not my info gleaned from the internet


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post #4 of 19 (permalink) Old 05-14-2019, 06:23 PM Thread Starter
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Re: P0171 trouble code

Kinda losing my mind over this.

I've smoked the intake several times, nothing comes out anywhere.

I certainly don't have an exhaust leak on that bank as there is no noise and I can't feel anything coming out from around the exhaust manifold.

I even went as far as to replace the intake manifold gasket for good measure and all the data is the exact same.

Scan tool shows 14% bank two and 25% bank 1 for fuel trim

Idle the MAF shows something like 1.8lb/min at idle and over 12lb/min when whapping the throttle.

Any other ideas? VVT possibly but not show other codes like cam/crank sync etc....? I am only getting the P0171 code and that's it.


I'm about ready to just roll her off a cliff or burn her to get insurance money

Last edited by Jay Moore; 05-14-2019 at 06:26 PM.
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post #5 of 19 (permalink) Old 05-15-2019, 12:57 AM
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Re: P0171 trouble code

https://www.justanswer.com/nissan/8w...n-new-oem.html


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post #6 of 19 (permalink) Old 05-15-2019, 12:59 AM
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P0171 trouble code

So anything over 12% is not good to much air hope that link gives you some ideas


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post #7 of 19 (permalink) Old 05-15-2019, 04:51 AM
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Your fuel trims are high on both sides. If you don't have a vacuum leak, or an intake air leak behind the MAF, you have an exhaust manifold crack, or you have a misfire causing your O2 sensors to see too much oxygen and throw more fuel at it. I'm still thinking air leak, with both banks being well above 10 on fuel trims. And is that short or long term trim value? Or combined?
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post #8 of 19 (permalink) Old 05-15-2019, 08:15 PM Thread Starter
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Re: P0171 trouble code

Thank you gentlemen, I'll have another look tomorrow. Maybe clean the MAF before replacing it.

I did a balance test pulling injector and ignition coil connectors and they all made a difference so I don't think I have a misfire. It also idles good and has plenty of power.

I am leaning still towards vacuum leak, but I did smoke it and the only smoke comes out the air filter housing, nowhere else.

Possibly clean the MAF sensor, I'd hate to replace it and have it not be the problem as they are expensive to me.



Thank you all for the help, I'll keep everyone posted on my findings.
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post #9 of 19 (permalink) Old 05-16-2019, 05:19 AM
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Re: P0171 trouble code

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Originally Posted by Jay Moore View Post
Thank you gentlemen, I'll have another look tomorrow. Maybe clean the MAF before replacing it.

I did a balance test pulling injector and ignition coil connectors and they all made a difference so I don't think I have a misfire. It also idles good and has plenty of power.

I am leaning still towards vacuum leak, but I did smoke it and the only smoke comes out the air filter housing, nowhere else.

Possibly clean the MAF sensor, I'd hate to replace it and have it not be the problem as they are expensive to me.



Thank you all for the help, I'll keep everyone posted on my findings.


Like I mentioned is the air filter housing on correctly it is real easy to not get it closed right.


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post #10 of 19 (permalink) Old 05-16-2019, 06:28 PM
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post #11 of 19 (permalink) Old 05-16-2019, 07:07 PM Thread Starter
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Re: P0171 trouble code

Cleaned MAF and put some clamps on any questionable hoses like PCV valve hoses etc......

I disconnected battery and clamped + and - together and held brake pedal down to discharge the computer.


It seemed better and everything was good, 02 data looked normal and so did the fuel trims and then maybe after a few trips and about 50 miles bank 2 is now throwing the same code, lean, and fuel trim goes from 0% to 25% on bank 2. At least the 02 sensor on bank 2 switches, but at extremes.

I decided to look at wiring and harnesses and I don't know what the Fudge I found. I do not think it is stock. I removed battery and battery holder box, removed the ECM harnesses and opened it up and this is what i found. Is this stock? It can't be in my opinion but I don't know, never ripped into a Titan ECM harness that I can remember.
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P0171 trouble code-20190516_213038.jpg   P0171 trouble code-20190516_213033.jpg   P0171 trouble code-20190516_213009.jpg   P0171 trouble code-20190516_213018.jpg   P0171 trouble code-20190516_213014.jpg  


Last edited by Jay Moore; 05-16-2019 at 07:09 PM.
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post #12 of 19 (permalink) Old 05-17-2019, 06:56 AM
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Re: P0171 trouble code

Hell no someone did some messing around there


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post #13 of 19 (permalink) Old 05-17-2019, 09:34 AM Thread Starter
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Re: P0171 trouble code

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Originally Posted by noel55 View Post
Hell no someone did some messing around there


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Thank you for the reply. I didn't think that looked normal or stock.


I am very good at soldering as electronics is my day job. What should I do? Should I take my time and remove all scrupulous wiring, inspect and most likely redo all fudged connections with a nice clean solder connection and heat shrink tubing? I feel it could solve my problem and also make the truck much more reliable in the future. Or should I just try and purchase a whole new wiring harness from Nissan and call it a day?
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post #14 of 19 (permalink) Old 05-17-2019, 11:26 AM
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Re: P0171 trouble code

Oh no, someone did a number there. Probably just twisted them together and wrapped with tape. I would remove each suspect wire one at a time and verify they are soldered together correctly. If not then solder and apply heat shrink or a solder butt splice and heat gun. I hate to see that bro, good luck.

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post #15 of 19 (permalink) Old 05-18-2019, 08:21 AM
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Re: P0171 trouble code

As poster above said first try taken each apart and resoder them put heat shrink on them see if that helps other wise yes you may need a new harness. I canít figure why someone would have done that unless it was in an accident and some goober was trying to cheat and make free cash by putting it on the insurance claim.


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