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Amedee, Lincoln Technician
Category: Lincoln
Satisfied Customers: 26244
Experience:  ASE certified Technician advanced level specialist. Wisconsin certified emissions state inspector
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Lincoln Navigator I have a 2001 Lincoln Navigator, engine

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I have a 2001 Lincoln Navigator, engine light on. Auto zone tested it and said the code was PO 171. Is this a oxygen sensor or MAF sensor? What do I replace as most possible cause?
Hello and Welcome to Just Answer. My name is XXXXX XXXXX I will try my best to assist you and your 100% satisfaction is my goal. I have been working on these vehicles for over 10 years so I am very familiar with this system and how they work. However, keep in mind, that I need some solid concrete facts/evidence/clues from you in order to give you a good answer about your vehicle. Please realize that all my answers are based solely on the info that you provide me with....

You could have a bad mass air flow sensor. Or the snorkel from the mass air flow sensor to the throttle body could be ripped. Both are very common and can cause you vehicle to loose power along with many other drive ability issues. First look for cracks or rips or anywhere air can enter the engine that is not accounted for by the mass air flow sensor. Next comes the Mass Air Flow (MAF) sensor. This is a very important sensor input to the computer. It uses a hot wire sensing element to measure the amount of air entering the engine. The MAF sensor then outputs an analog voltage signal to the PCM proportional to the intake air mass. The PCM calculates the required fuel injector pulse width in order to provide the desired air/fuel ratio. If the sensor is bad than this air/fuel ratio will be off causing severe performance issues. In extreme cases, I have seen these two problems cause a no start condition. This input can also be used in determining transmission Electronic Pressure Control, shift and torque converter clutch scheduling. The check engine light may even pop on if the sensor is bad, the snorkel is ripped or a tube has fallen off. This will result in a lean condition.

You might have an air or a vacuum leak. This is very common! Open the hood and listen for a hissing sound when the engine is running.
Unmetered air can enter the engine through a vacuum leak, a dirty airflow sensor that is not reading airflow accurately, an EGR valve is not closing and is leaking exhaust into the intake manifold, an EGR valve that is allowing too much flow.
If it is hard to pinpoint take some brake cleaner or starting fluid around the intake manifold and vacuum lines and see if the engine stumbles or if the idle is affected. Be extremely careful when doing this!

Possible Causes
Check for air leaks in the Air Induction system (e.g., in the intake manifold)
Check for air leaks in the PCV system and in its related hoses and/or valve
MAF sensor is dirty, "skewed" or installed improperly
Throttle plate, throttle shaft or linkage is damaged or sticking
Customer: replied 6 years ago.


I have not seen any of these areas affected? Unless I missed it.Does the MAF need to be replaced or can it be cleaned? The auto zone man said it was the oxygen senor upper bank 1? What does this mean or is he guessing?


This is a lean code. Although an oxygen sensor could cause this, it is usually a bad mass air flow sensor or a vacuum leak.

YES... you can try to clean the mass air flow sensor if you like. I use PC circuit board cleaner. If the mass air flow sensor is bad and cleaning does not improve the readings at all, the mass air flow sensor will need to be replaced.
Customer: replied 6 years ago.


Where is this oxygen sensors located? They said on passenger side, but where are they at they said there was upper and lower bank oxygen sensors 4 of them on this truck?

MAF are rather high to guess at one. What would be the best solution in my case? What would you do?

Also clearing the engine light/ Is the only way for me to do this is to take the battery cable off and put back on? I have no tester.

There are two of them on each bank. Once before and one after the converter ...on each bank.

Your best solution is to look for vacuum leaks under the hood very careful. In addition, you would need to get your hands on a scanner that can read live data. YOu need to check your baro reading in your computer to see if it is correct. If not, your mass air flow sensor needs to be replaced.. hands down!
Customer: replied 6 years ago.


OK- so your strong on a vaccum leak or MAF. Correct?


Also what about clearing the engine light. Is this the only way for me to do it? Will it hurt anything?

OK- so your strong on a vacuum leak or MAF. Correct?


Also what about clearing the engine light. Is this the only way for me to do it? Will it hurt anything?

It is better to clear the code in your computer with a scanner or a code reader. However, you can disconnect the battery to do this as well if you would like.
Customer: replied 6 years ago.


Ok, Thank you. Trying to save a expensive repair bill.


Although auto zone paper says oxygen sensor with your experience you say it is not that causing my problem?

THat is correct. The code says oxygen sensor indicates that the ENGINE is running lean. There are several things that can cause the engine to run lean.
Amedee and 6 other Lincoln Specialists are ready to help you
Customer: replied 6 years ago.
This did not fix my problem?

Did you replace the mass air flow sensor?
Customer: replied 6 years ago.
Yes, the code still says the same.
Did you check the baro reading in the computer? Did you recheck for vacuum leaks?

Edited by AMEDEE on 1/30/2011 at 6:47 PM EST
Customer: replied 6 years ago.

I checked for vaccum leaks by spraying carb. cleaner around everything and no change in motor speed.

I do not know what your referring to about a baro reading?

Auto zone still says it a oxygen sensor bank 1 upper passenger side. Another 50 and the work to replce it. I have not yet. I could have took it to a service garage and paid the big dollars.

It sounds ot me like you just have a vacuum leak and did not look hard enough for it. This is very common on this engine. If the mass air flow sensor checks out ok or has been replaced, then I would go after a vacuum leak next. The intake gaskets and the pcv hose are very common culprits on this vehicle.

Click here

Customer: replied 6 years ago.

I will work with it some more today and tomorrow.



You bet!
Customer: replied 6 years ago.
Hi, Your suggestion still did not repair my truck. I guess I'm going to need to make a appointment with a shop to find the answer and bite the bullet.

Did you check for vacuum leaks or replace the mass air flow sensor?
Customer: replied 6 years ago.
Hi, Both.
How did you check them both?

What were the readings from the mass air flow sensor?
Customer: replied 6 years ago.
Remember I do not have a scanner. Do not know?
THen how did you check the mass air flow sensor?
Customer: replied 6 years ago.
You told me to replace it from the reading that I got from autozone. So I did. It was a pain to get out but I was careful and replaced it, and cleaned area with cleaner. I used starting fluid to spray on vaccum lines to see if motor would change speeds or not. As you know they are alot of hoses, I could be missing something?
IT is possbile!

Your still getting a p0171 correct?
Customer: replied 6 years ago.
Pay close attention to the PCV hose and tubing. In addition, check the intake gaskets and verify that the fuel pressure is ok.
Customer: replied 6 years ago.

I will take another look at it. I know its hard not seeing it yourself. Maybe a scanner is my next choice of tools to get. I will need to see what is a good one for all vehicles if possible. Auto-zone had a hand held scanner that seemed to work OK if it is correct?


I'll let you know

Customer: replied 6 years ago.
They keep telling me oxygen sensor, but I'm spending way to much money and time and not fixing my problem! Dont want to replace everything there. HA.
This is a lean code. Oxygen sensors can cause this code. However, 9 times out of 10 is is a vacuum leak or a bad mass air flow sensor. Be sure to check the PCV hose/valve.
Customer: replied 6 years ago.

I will and will let you know.



You bet!
Customer: replied 6 years ago.

Had my truck checked. I wasted $18.00 with you. It was none of what you said. It was dirty fuel injectors. Thanks for nothing.




I am very sorry to hear that. I have never come across dirty fuel injector causing a lean code. IF this were the case, you should have felt some severe lack of performance issue under a load or hard acceleration.

I did also state that there were several things that can cause your engine to run lean. Remember, this web site is for informational purposes only. I am not there in front of your vehicle running the tests. All I can do is point you in the right direction.