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DIY: Do It Yourself
Post here to share or improve your wrench turning skills! All BMW E46 DIY tips, tales, and projects discussed inside. Learn to work on your car and know the right BMW parts you will need!

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Old 07-15-2010, 08:36 PM   #1
adriver
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My story with P0171 and P0174 (cliffs; cheapest maf fix ever!).

Well it first started with getting a few more codes than that. I tried to go cheap and had time, so I started by checking for a vaccuum leak. I first found my upper intake boot had a nice crack in it. I sealed it with silicone and it seemed to fix things, at least enough to drive it, but was still having problems. I tried MAF cleaner, I cleaned the throttle body, checked the disa valve, cleaned the idler valve, found that my lower intake boot was just as bad, and replaced that as well, and still had the problem. Then I went to the other side, I replaced the valve cover seals, spark plugs, and rebuilt the vanos; still had the problem. Well searched of course and tried to avoid, but the winner is.. EBAY. I am the guy who will search every auto parts store, ebay, Clist, etc... spending a few hours to save a few bucks. All of a sudden I found this.
http://cgi.ebay.com/ebaymotors/BMW-3...item4151210c2f
for 61.99 shipped.. I couldnt even get a used one off C list for this price both people I asked what $70. I paid for it late monday night, and the seller hyper_auto is in NC, I received it in TX by Thursday. Spent 2 minutes installing it, and I am very happy to say the car is now running beautifully again. I am not affiliated with the seller or anything, just a very happy DIYer who wanted to share what IMHO is the cheapest way you will ever solve these codes.
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Old 07-15-2010, 08:51 PM   #2
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i have the same problem, and replaced everything you did except the vanos, i did also replace the disa and the maf, but still have the codes. i think it may be my gas cap... don't know what else it could be. i did get the light off long enough to pass emissions so i am good for another year, the car is running good but the codes still appear.
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Old 07-15-2010, 09:07 PM   #3
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maybe this could help

Quote:
OBD II Fault Code

* OBD II P0171
* OBD II P0174

Fault Code Definition

* OBD II P0171 Fuel System Too Lean (Bank 1)
* OBD II P0174 Fuel System Too Lean (Bank 2)

Symptoms

* Check Engine Light will illuminate
* In some cases, no adverse conditions may be noticed by the driver
* In other cases, there may be performance problems, such as a lack of power on acceleration and some "coughing" or misfiring
* The vehicle may have trouble idling, especially when warm or when sitting at a stoplight

Common Problems That Trigger the P0171 and P0174 Code

* PCM software needs to be updated
* Vacuum leaks (Intake Manifold Gaskets, vacuum hoses, PCV hoses, etc.)
* Mass Airflow Sensor (MAF)
* Plugged Fuel Filter or weak Fuel Pump
* Plugged or dirty Fuel Injectors

Common Misdiagnosis

* Oxygen Sensors

Polluting Gases Expelled

* NOX (Oxides of Nitrogen): One of the two ingredients that, when exposed to sunlight, cause smog
* HCs (Hydrocarbons): Unburned droplets of raw fuel that smell, affect breathing, and contribute to smog

The Basics
Combustion engines operate by burning an air/fuel mixture of about 14.7 to 1-14.7 parts air to 1 part fuel. When the air ratio goes below 14.7 parts, this is called a "rich" mixture. If the air rises above 14.7 parts, it is called a "lean" mixture.

Rich Mixture = Too much fuel, not enough air
Lean Mixture = Too much air, not enough fuel

To keep the engine running properly, the Engine Control Module measures the oxygen content in the exhaust with oxygen sensors and makes adjustments to the mixture by injecting more or less fuel.

The control module operates within specific parameters and under normal conditions, it will make minor adjustments to the air/fuel mixture. When these adjustments become too large, a fault code is set. When the P0171/P0174 code sets, the oxygen sensors are detecting too little oxygen in the exhaust and the control module is adding more fuel than normal to sustain the proper air/fuel mixture.

P0171/P0174 Diagnostic Theory for Shops and Technicians
When a vehicle has the fault code P0171 and or P0174, it means that computer can no longer automatically adjust the mixture between air and fuel. Code P0171 applies to Bank 1 and P0174 applies to Bank 2. Code P0174 mainly applies to V6 or V8 engines because 4-cylinder engines generally have only one bank, though there are a few exceptions. Some of the high performance 4-cylinder and straight 6-cylinder engines (such as those in BMW and Lexus) split the cylinders into groups of two or three and call them separate banks.

When the code says that the Fuel System is "too lean," it means that the computer has been adding more and more fuel, which is called Long Term Fuel Trim. Ideally, the Long Term Fuel Trim should be close to 1 to 2 percent. When a code P0171 is set, it means that the Fuel Trim is anywhere from 15 percent to as high as 35 percent compensated. When this happens, the computer knows that there is an improper condition in the control of the Fuel System.

The first step in the diagnosis of a code P0171 and/or P0174 is to look at a minimum of three ranges of the Long Term Fuel Trim numbers on a scanner. Check the idle reading-3000 RPM unloaded and 3000 RPM with at least 50 percent load. Then check the freeze frame information for the code to see which range(s) failed and what the operating conditions were.

Before we get into the main causes of P0171, let's explore why this code matters.

Why Does a P0171/P0174 Code and Running "Too Lean" Matter?
"Lean" running cars and light trucks are highly polluting vehicles. Most of the NOx pollution, which is poisonous and can cause asthma, is caused by vehicles that are running too lean. A lean running car can also misfire, which puts raw fuel (HCs) into the atmosphere. When you are behind a car or truck that smells bad and makes your eyes burn, it is misfiring and running too lean. In comparison, a "rich" running engine has no smell (CO is odorless) or you may detect a rotten egg smell, which is caused by the Catalytic Converter consuming too much sulfur, like when you are behind a big SUV at full throttle going up a long, steep hill.

P0171 is not an Oxygen Sensor problem. Before a P0171 code is possible, the computer first ran a series of tests to validate the readings from the oxygen sensors. Since the oxygen sensors passed their readiness tests and didn't set any codes, the computer then looked to the Fuel Trim adjustment. When the computer determined the air-to-fuel mixture to be too lean, it then set the P0171 code.

What Are Some Common Causes of Code P0171/P0174?
Always check to make sure that there is not a PCM software update due or available. Often, as the vehicle's engine wears, the PCM's Fuel Map software inaccurately compensates for this condition. The fuel mixture grows lean and eventually, the code sets.

A vacuum leak is very common. It could be a torn PCV hose, a torn Intake Air Boot, or even a broken seal on the dipstick (the dipstick is a part of the PCV system and if it does not seal, too much unmetered air will enter the engine). Don't rule out a sticking/leaking EGR Valve or leaking EGR or Intake Manifold Gasket. If it is a V6 or V8 engine and the code is only on one side/bank, it could be a defective Intake Manifold Gasket or cracked/leaking manifold.

What if There Is No Vacuum Leak or Both Codes (P0171 and P0174) Set?
An "under reporting" Mass Air Flow Sensor can be a common cause of a code P0171 and P0174. Essentially, this means that the Air Flow Sensor is telling the computer that much less air is entering the engine than actually is.

Since the oxygen sensors are telling the computer that more fuel is needed, this causes confusion in the computer because the Mass Air Flow Sensor is still saying there is too little air and the Oxygen Sensor is reporting that the mixture is still too lean. The computer tried to compensate, but since resolution is impossible, it sets the code. It is important to restate that the Oxygen Sensors are accurate-the fuel mixture is too lean. In this case, the Air Flow Meter or Sensor is inaccurately reporting the real amount of air entering the engine.

How Do I Know if the Problem Is the Mass Air Flow Sensor?
There is a very effective "truth test" for any Mass Air Flow Sensor. Start the engine, let it idle, and then check the Barometric Pressure reading on the scan tool data. If the reading is about 26.5 Hg and you are close to sea level, you know that you have a defective Air Flow Meter because it is telling you that you are at about 4500 feet above sea level. (These conversion tables will help.) When the Mass Air Flow Sensor sees this Barometric reading, it adjusts its Air Density table and then "under reports" the actual amount of air entering the engine. It does this because the Barometric Pressure Sensor is actually part of the Mass Air Flow Sensor.

Sometimes the Air Flow Sensor and the sensing wire get covered with dirt, dust, or oil residue, which can also set a P0171. Cleaning the sensor might hold off problems for a while, but eventually, the MAF sensor should be replaced. Always make sure the Air Filter and its enclosure are dirt-, dust-, and oil-free. If you clean and replace the filter and its enclosure as needed, you will prevent the new MAF from failing.

Additional Causes of Code P0171/P0174

* A plugged Fuel Filter or poorly functioning Fuel Pump can set the P0171 code. The computer hears (accurately) from the Oxygen Sensor that the Fuel Mixture is too lean so the computer keeps increasing the amount of fuel being delivered into the combustion chambers. But in this case, the Fuel System can't increase the amount of fuel.
* If you still can't find the problem, be sure to check and verify that fuel pressure and delivery are at spec. If fuel pressure and volume check out okay, scope the injectors and perform injector drop and/or flow tests to see if they are capable of delivering enough fuel. Dirty/contaminated gas can definitely plug injectors and trigger these lean codes.
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Old 07-15-2010, 10:20 PM   #4
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FYI, this will only work for MS43 DMEs. MS45 (LCI coupe and ZHP) and M56 (SULEV) use different MAF which is way more expensive.
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Old 07-15-2010, 10:57 PM   #5
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Just curious... When I got my codes read, it was at advance autoparts, and the generic code reader they had, plus all I could find on here is "bank 1 lean" "bank 2 lean". There is a shop around here that will dyno pull along with an air/fuel reading. Knowing that reading is supposed to be close to 14 o so, Could someone be able to get a dyno run; an air/fuel reading (for about $50) and be able to tell from that whether you are not getting enough air or fuel depending on if it is higher or lower than what a normal reading should be?
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Old 07-15-2010, 11:09 PM   #6
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guys i had the same thing in my car and it turned out to a be a very small crack in my dipstick case..... maybe check there if you have not already....
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Old 07-16-2010, 06:09 AM   #7
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P0171 P0174 fixed by just easily replacing one oil separator hose

For those with P0171 and P0174 codes, but without known causes yet, you might take a look at the easily accessible lower oil separator valve hose, which goes from the oil separator down to the dipstick tube. It is not hard to find, check (it usuallly breaks in two near the oil separator end, but could be just split there at an early stage) and replace (only $10 for the hose). It can definitely set off several Fuel trim codes and others. The following post/thread (with good PICTURES) shows you where to find it (just have too take the air filter box out). It might be your easy fix to an annoying problem.

http://forum.e46fanatics.com/showthread.php?t=773551

Last edited by gsbmw; 07-20-2010 at 07:27 AM.
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Old 07-16-2010, 10:28 AM   #8
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i have also replaced the oil seperator/pcv valve assembly and hoses and the fuel filter. o checked the upper and lower intake boots and both seem fine, i have sprayed carb cleaner around evrything while idling and noticed no difference.
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Old 07-16-2010, 11:13 AM   #9
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are these codes the same as Peake 1b 62 and 63 (catalyst system efficiency)?
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Old 07-16-2010, 11:23 AM   #10
Rif Raf
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When my car threw these codes, it turned out to be a leaking vac line at the valve that the Secondary Air Pump runs to. The little vac line!
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Old 07-16-2010, 10:40 PM   #11
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Quote:
Originally Posted by Tmw325i View Post
i have also replaced the oil seperator/pcv valve assembly and hoses and the fuel filter. o checked the upper and lower intake boots and both seem fine, i have sprayed carb cleaner around evrything while idling and noticed no difference.
I feel for you. I've replaced the fuel filter, MAF, re-sealed the DISA, inspected upper and lower intake boots, and sprayed down almost the whole engine looking for a vacuum leak. I still haven't found one, but my car still tests my sanity by popping up P0171 and P0174.
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Old 07-16-2010, 11:11 PM   #12
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Quote:
Originally Posted by gsbmw View Post
For those with P0171 and P0174 codes, but without known causes yet, you might take a look at the easily accessible lower oil separator valve hose, which goes from the oil separator down to the dipstick tube. It is not hard to find, check (it usuallly breaks in two near the oil separator end, but could be just split there at an early stage) and replace (only $10 for the hose). It can definitely set off several Fuel trim codes and others. The following site shows you where to find it (just have too take the air filter box out). It might be your easy fix to an annoying problem.

http://forum.e46fanatics.com/showthread.php?t=773551
I may drive up to LA tonight just to personally say thank you. I just went out to the garage, and sure enough my hose is in 2 pieces. Let's hope this clears up the issue once and for all.
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Old 07-20-2010, 07:23 AM   #13
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I'm glad I could help you out! I know I've been helped many times here, so after finding this broken hose on my car, I just thought this relatively undescribed (on its own) problem should be put out there for people to benefit from. But I sense that it may be common, given that many people replacing their PITA oil separator and hoses often find that only this easily replaced hose is broken. Unless you have another vacuum leak somewhere, this repair will probably take care of your codes. It worked for me.
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Old 07-30-2010, 10:11 AM   #14
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RE: MAFS from-- http://cgi.ebay.com/ebaymotors/BMW-3...item4151210c2f

I have a 2003 325i; I purchased this MAFS but found that it had an incompatible connector plug. Three flat pins; my plug has 5 pins (five wires) with one blank.
I found one on Autozone but it is from Cardone (Remanufactured) for $200; the new one is $300 to 400; has anyone used a Cardone part before?
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Old 08-02-2010, 12:12 PM   #15
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Would you guys use a Cardone rebuilt part or do you strickly recommend a new MAF Sensor?
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Old 11-01-2010, 07:46 PM   #16
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I'm actually one of the victim from the same ignoring codes: (P0171/P0174) I did whatsoever take care some other locations that were apart of these codes: by replacing (Fuel filter) (All oxygen sensors) (New Oil separator/Hoses that were cracked, melted) (Cleaning out the Air mass sensor) Otherwise! I've sprayed all around the intake to investigate some different idles. But, nothing seems to be found. Literally!!! The (X5 4.4i M62) engine is running much better now after replacing all these parts, flying on highway smoothly; but a little bit slow hesitation on acceleration when 1st pressing the gas pedal to speed-up. (This is a good sound of mass airflow sensor) that probably needs to be replaced. Otherwise codes takes much longer to appear now than before, and they're showing on two different ways as: P1158/P1160 sometime switching to P0171/P0174 or all 4 of them at the same time.

(2001 BMW X5 4.4i M62 112,783 miles)
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Old 11-01-2010, 08:30 PM   #17
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Oil separator/bottom hose replaced

Quote:
Originally Posted by Leets View Post
I may drive up to LA tonight just to personally say thank you. I just went out to the garage, and sure enough my hose is in 2 pieces. Let's hope this clears up the issue once and for all.
You probably right!!! however for the past 3 days, I've been working hard on this location specially removing the Oil separator to put a new one. @1st, I didn't know how the bottom Oil separator to the distick looking like. When I finished removing the top hoses with the two screws, I tried to pull it up a little slightly
but before I can pull harder, the little hose from the bottom raped-off in my hand like a peace of paper. this is to show you how bad the hose were melted apart inside. However I didn't have the hose handy but I wen't to Autozone and they found me something similar much resistant that can fit there the same way, and I put clamps on all hoses. But unfortunately after 80 miles driving, codes still appears as: (P1158/P1160/P0171/P0174)

01 X5 4.4i M62
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Old 10-16-2011, 01:26 AM   #18
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Quote:
Originally Posted by Tmw325i View Post
i have the same problem, and replaced everything you did except the vanos, i did also replace the disa and the maf, but still have the codes. i think it may be my gas cap... don't know what else it could be. i did get the light off long enough to pass emissions so i am good for another year, the car is running good but the codes still appear.
i replaced the gasket on the disa valve lean codes showed up in a matter of minutes mostly bank one but would also affect bank 2 a few times also replaces all sorts of emmision related crap oil seperator plastic hoses intake boots broken vaccum lines cleaned maf but in the end it was suking air from the gasket around the disa were it bolts to the manifold that gasket was flat as a chick with no ass but got rid of my lean codes for good fuel trims back to %0.0 on both banks. hopes this helps 2001 330i 167000mi..
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Old 04-25-2014, 02:03 PM   #19
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My 2004 BMW 330Ci was throwing these codes every time I took a trip over an hour long. After spending a ton on a new air intake boot, fuel filter, fuel pump, ERG system, and tune-up (in that order), my issue ended up being a bad MAF sensor.

Ever since I changed the MAF, I never got the codes again and my car seems to be running smoother and have more pep.
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