# 2001 Pathfinder LE SES P0171 ...



## slacker01 (Sep 12, 2005)

So SES came on my Pathfinder came on couple of weeks ago. I tried closing the gas cap little tighter just in case After few drives, the light went out for couple of drives then SES came back on.

I begin to wonder if running gas close to empty on few occasions may have caused it but light never went out after couple of fill ups and few trips.

Finally, I rushed to Autozone to get code read. P0171. System Too Lean (Bank 1). The guy said something like it could be fuel injector or many other things. Better take it to a shop, he said.

So I didn't. I am going to try to figure out what the problem is before I let the dealer rob me.

It's probably not gas cap but I think I'll go out and get a new one since it's only few bucks.

From what I gather, it looks like it's MAF in many cases with P0171 for Pathfinder.

I bought a modest scanner, Actron P9175. To save on trips to Autozone and to see if I can get any additional info... (and because my wife let me...)

I/M Monitors (Emissions Systems) monitor on the scanner all returned ok... So I guess that means all the monitors are working alright.

Looked at Freeze Data when P0171 triggered.

Engine RPM : 2312
Coolant Temp: 192 F
Short Term Fuel Trim1 : -4.6%
Long Term Fuel Trim1 : 32.0%
Short Term Fuel Trim2 : 2.3%
Long Term Fuel Trim2 : 30.4%
Short Term Fuel Trim3 : -100.6%
Long Term Fuel Trim3 : -100.6%
Short Term Fuel Trim4 : -100.6%
Long Term Fuel Trim 4 : -100.6%
Vehicle Speed : 64 mph
Fuel System 1 : CLSD
Fuel System 2 : CLSD

If anyone notice anything interesting in above Freeze Data, any input would be appreciated.

I got a MAF contact cleaner. I think you can get similar sensitive electronics component cleaner from Radio Shack. I cleared the SES but haven't had time to try cleaning MAF yet. I will report back as to my success or failure.

I just want to log my problem here for others with same problem.


----------



## slacker01 (Sep 12, 2005)

The cleaning was pretty easy. You need Torx T20 security bit. They try their best to make sure simple things are unnecessarily hard for DIY people. I had regular Torx bit but not security bit so I had to run to Sears to pick one up. ($9.99 for 6 assorted torx security bits)

1) Locate the MAF sensor. Find air filter casing. Follow it back to the engine. It's close to the air filter casing. It's hard to miss. I am only taking out the sensor instead of the whole MAF casing.
2) Take off wiring harness.
3) Take off couple of screws using torx T20 security bit.
4) Pull out the sensor. It take little bit of force and wiggling.
5) Spray the cleaner on to two areas that I can see shiny metal. Give it a good spray bath.
6) Let it air dry.
7) Replace the sensor.
8) Spray the cleaner on the wiring contacts.
9) Let them dry.
10) Plug the wire.

Let's hope this works out. I erased the codes using my OBDII scanner. Unlike O2 sensors, I believe MAF do not require any additional clearing steps.

I will report back in couple of days and announce if SES light comes back on or not. I have to replace tires on this Pathfinder so I am hoping to avoid any extra cost of MAF replacement or other services.


----------



## 2001pathy_SE (Apr 9, 2006)

keep us updated.


----------



## slacker01 (Sep 12, 2005)

It's been two days. I made several errands on this car. I did not drive for a extended distances (no more than 5 miles at a time). SES light is still off. The car seems to respond better with gas pedal but it could just be my mind playing with me.

Many people claim better gas mileage and performance after cleaning MAF...

I'll report back if SES light comes back on with same code but so far so good.


----------



## slacker01 (Sep 12, 2005)

Well, SES came back on tonight. What I found interesting is the freeze frame information which seems similar with the information I got initially. Same speed and RPM which is very curious. The light didn't come on when I was driving around town. After couple highway trips SES came back on.

Engine RPM : 2312
Load Value : 46.2%
Coolant Temp: 190 F
Short Term Fuel Trim1 : 7.0%
Long Term Fuel Trim1 : 32.8%
Short Term Fuel Trim2 : -4.6%
Long Term Fuel Trim2 : 30.4%
Short Term Fuel Trim3 : -100.6%
Long Term Fuel Trim3 : -100.6%
Short Term Fuel Trim4 : -100.6%
Long Term Fuel Trim 4 : -100.6%
Vehicle Speed : 64 mph
Fuel System 1 : CLSD
Fuel System 2 : CLSD


I am not sure what this means now. Car drives fine.

Any one have any additional thoughts? Maybe cleaning wasn't good enough and MAF has gone bad?

On unrelated note, the steering wheel used to shake quite a bit 55-65mph. I had the tires balanced at a shop that had Hunter GSP9700 with road force as suggested by another post on this forum. Shaking is gone.


----------



## slacker01 (Sep 12, 2005)

I think I may have found the problem with my pathfinder. I should've checked this first I guess. While I was changing oil on the Pathfinder, I pushed on the duct that leads to engine block unintentionally.

It moved more than I anticipated. I checked the hose-clamp where it makes connection to engine block. What do I notice? Very lose clamp. I tightented the clamp.

Hopefully, that'll clear up the P0171.


----------



## fcp18 (Oct 16, 2006)

Hi there, 
Im having pproblems with my 2001 Pathfinder LE. For a month now ive been getting P0171 and p0174 error codes. The manufacturer service tech manual states the following as the possible causes in this order:
Air Intake Leaks 
Front o2 sensor
Injectors
Exhaust gas leaks
Incorrect fuel pressure
Lack of fuel
MAF sensor

Have not taken it to the dealer yet because this is a non specific code and I dont have very much faith in them. However the driveability of the vehicle has been affected. It hesitates, lurches and loses power especially when accelerating. I have cleaned and monitored the output of the maf sensor during operation and the output seems to be well within spec. Have also scoped both front o2s and found the right bank slow in responding at times. Replaced it. Same problem. Replaced air filter, fuel filter and visually checked for air intake leaks. Nothing obvious. Next thing I guess would be to have injectors cleaned, monitor fuel pressure, and possibly have the air sytem smoked out for leaks.
The problem with this code that it does not point to a hard fault on any one device. Anyway any help out there would be helpful and I will also report back any findings as this could be a common problem.


----------



## BlackLE (Mar 13, 2007)

I just bought an '03 Pathfinder LE and i am getting this code aswell, did anyone find the problem that was causing the code?


----------



## pstephens1 (Feb 2, 2007)

Have you checked all your vacuum line? What about your air filter? It would seem you might have some type of air flow problem....these are the 2 cheapest fixes the next would be the air flow meter which can be costly 150 or more


----------



## slacker01 (Sep 12, 2005)

PROBLEM RESOLUTION:

I drove this car for a year without much problem with P0171 code on. However, IL requires emissions test so I had to fix it. I finally gave in and took it to a mechanic. I didn't want to take a chance with replacing MAF sensor myself since part cost $500 since I wasn't sure it was the problem 100%.

The mechanic first suggested cleaning MAF sensor. I told him I already try it. So he ran a vacuum seal test with colored smoke. He didn't find any problems. He then looked at the diagnostic data and noticed the trim figures were way too high. He said under normal driving conditions it should be generally at 5% at most but he was seeing 30%. To make long story short, in this case MAF sensor is bad causing fuel trims to go little crazy.

With labor, tax, and $500 MAF sensor part, I paid $700. The light is off now and it hasn't come back for a week. He basically charged me MSRP for OEM MAF sensor which he had to get it from a Nissan dealer. You can probably find it few bucks cheaper if you did it yourself.


----------



## smj999smj (Jan 1, 2006)

This seems to be a common failure on Toyota SUV's as well...I wonder if they both use the same manufacturer for their mass air sensors?


----------



## slacker01 (Sep 12, 2005)

Well, SES light came back on. This time it's P0138. It looks like there's more problem to fix with my Pathfinder.


----------



## etepsnewo (Jul 5, 2008)

*Sounds farmilar*

My 95 Sentra ( 200sx ) has a code of PO170 for some time now. The engine is very sluggish especially when cold. Every mechanic I talked to said, " Replace the MAF." Why do they always recommend starting with replacements of the most expensive parts first? LOL I have three of these cars so I cleaned the MAF sensors and swapped them out with no change at all. I went through all the vacuum line replacements, etc. and used propane and carb cleaner spray to look for vacuum leaks everywhere. Replaced the throttle position sensor, oxygen sensor, variable valve timing solenoid. All of this did needed to be done but still the sluggishness when cold and the code persists. Yesterday I started looking into the fuel system, bought a fuel pressure gauge and did a leak down test. I think I have found the problem. My Fuel Pressure regulator is still allowing fuel to return to the gas tank via the return line even when the vacuum drops on acceleration. It is stuck open or not closing all the way when it should ! I put a fuel shut off valve in the fuel return line and guess what? When you block the fuel with it from going back to the tank while you open the accelerator the engine revs up like it should even when cold . If you leave that valve open the engine spits and sputters because it is doesn't have enough fuel flow and pressure. Kind of like your shower head when someone flushes a toilet while you are taking a shower in an old house. LOL I just ordered a new Fuel Pressure Regulator and a fuel filter. Can't wait to install the new parts and see how it runs etc.


----------



## smj999smj (Jan 1, 2006)

A fuel pressure leakdown test is not performed while the engine is running. It is used to check for leaking down injectors or a bad regulator when the engine is turned off. The system is energized by turning the key "on" and building up the pressure and the fuel line is crimped down before the fuel pressure regulator (some gauges have a valve to close on their hose to isolate the line). The fuel pressure drop is then measured over time and compared to the manufacturer's specs. 
Fuel pressure regulators are normally closed, meaning the fuel system will be at max fuel pump pressure output, and it opens as vacuum is applied to the diaphragm. This is why fuel pressure is first tested with the key on, engine off, to measure full system pressure from the pump, and then the engine is started and the pressure is checked, now with vacuum applied to the regulator, to see of the pressure is at the regulated spec. On most of the older Nissans, unregulated is usually around 40-45 psi and regulated pressure is usually around 34-36 psi. Around 2002, the QR25DE engine was released with a slightly different system and pressure specs rose to 50 psi and eventually found its way to other engines and models. 
Since you didn't post your regulated nor unregulated fuel pressure test readings, I can't say whether your regulator is bad or not, but it certainly could be.


----------

