P0171 system too lean bank 1 - Toyota Nation Forum : Toyota Car and Truck Forums
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#1 Old 11-01-2009, 12:45 PM
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P0171 system too lean bank 1

hey i recently pulled this code on my corolla i took to the dealer and they said that my mass air flow sensor was bad and i had it replaced. Well just the other day the engine light came on again and the same p0171 code came up. Was just wondering what to check next. Thanks
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#2 Old 11-01-2009, 01:18 PM
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did you or did you not replace the sensor? its not clear there. things besides the MAF can cause that code. an air leak after the MAF, an exhaust leak, or a bad oxygen sensor are also common causes.
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#3 Old 11-01-2009, 01:53 PM
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i have been getting that code recently.

I cleaned my MAF (which was filthy from air filter oil after 80K), and reset the code.

I then got it 2K miles later, which I reset. then 200 miles later and I reset, and I have not gotten it back yet.(3K miles).

Im not sure whats up with that. try resetting it yourself and see if it comes back. (you can reset by pulling the neg cable to the battery for 5 - 10 mins)

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#4 Old 11-01-2009, 08:45 PM
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How many miles are on the car??? If its over 100k miles, i would replace the o2 sensor anyways. Im guessing its the o2 sensor; quite expensive, but got to be replaced sooner or later anyways.

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#5 Old 11-01-2009, 09:12 PM
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are you getting a misfire or is the car running rough? if not then you're probably not running lean, which would indicate bad precat O2.
a bad O2 sensor tends to flip lean codes then cause the EMU to err on the side of rich.
indicators of a bad O2 include bad gas mileage, black smoke from the tailpipe, hesitation off the line picking up at higher end. also pull your spark plugs and post pics of what they look like. i'll do a diagnosis from there.
this is what i'm studying this semester at school so some red lights are going off.
looking at your plugs will be a BIG tell. (its what professional race techs look at to diagnose race motors)

before you ask a 'how do i...' question answer this for me. do you own a repair manual for it? have you searched the forum for a similar issue?

SEARCH THE FORUM BEFORE YOU POST!
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#6 Old 11-03-2009, 06:25 AM
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A vacuum leak from a crack pcv hose, vacuum hose or leaky intake manifold gasket could cause this. Another likely culprit could be partially clogged fuel filter or injectors. My wife's Chevy had a lean code, the mechanic tried the mass air flow sensor, plugs, fuel filter and it ended up being partially clogged injectors, he performed an injector cleaning service and all is well. Hope this helps you out

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#7 Old 11-16-2009, 11:33 PM
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just wondering where i might find the vacuum hoses?
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#8 Old 11-19-2009, 01:26 PM
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Vacuum hoses run all over the engine - you can't miss them. The trick is to find the bad vacuum hoses. Visual inspection can catch the majority of them, others, you need to get creative. There is vacuum diagram on the underside of your hood - a good idea to see if all the hoses are present. I could see a tech forgetting to put back a hose after doing some diagnostic work on the car.

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#9 Old 11-19-2009, 08:01 PM
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you can check for vacuum leaks by spraying carb cleaner all around. if you hear the engine rev there is a leak there. A code 171 suggest a maf issue, a vacumm leak issue or a fuel delivery issue. run some techron in it, clean the maf and check for leaks if that does not work change the fuel filter and do a fuel presure test.
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#10 Old 11-20-2009, 10:08 AM
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Quote:
Originally Posted by Downhillzze110 View Post
are you getting a misfire or is the car running rough? if not then you're probably not running lean, which would indicate bad precat O2.
a bad O2 sensor tends to flip lean codes then cause the EMU to err on the side of rich.
indicators of a bad O2 include bad gas mileage, black smoke from the tailpipe, hesitation off the line picking up at higher end. also pull your spark plugs and post pics of what they look like. i'll do a diagnosis from there.
this is what i'm studying this semester at school so some red lights are going off.
looking at your plugs will be a BIG tell. (its what professional race techs look at to diagnose race motors)
have you checked your spark plugs? first thing you do if your getting a lean code is check vacuum hoses then spark plugs. if your spark plugs show signs of lean firing then you have a intake leak. also when you pulled the codes did you get any P030X codes (misfire)? those will be a BIG tell if you have a manifold vacuum leak or a dirty MAF

before you ask a 'how do i...' question answer this for me. do you own a repair manual for it? have you searched the forum for a similar issue?

SEARCH THE FORUM BEFORE YOU POST!
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#11 Old 10-16-2011, 09:15 AM
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fixed my P0171 "Left bank running lean" code reading

I got the code P0171 recently and searched several forums for the definition and solution. Well, it seems that there are several possible causes, so I started with the cheapest solution first, cleaning the MAF sensor located in the large, curved, 3 1/2"-4" black rubber hose located to the right of the engine. I bought some MAF cleaner, sprayed it real good, gently used a q-tip around the resistor, put it all back together and so far, 100 miles later, the light is still out. The engine seems to be running smoother to. I would probably replaced the intake gasket next if that didn't work. Good Luck

Last edited by rdman7777; 10-16-2011 at 09:22 AM. Reason: misspellied text
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#12 Old 10-16-2011, 09:53 AM
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Quote:
Originally Posted by rdman7777 View Post
I got the code P0171 recently and searched several forums for the definition and solution. Well, it seems that there are several possible causes, so I started with the cheapest solution first, cleaning the MAF sensor located in the large, curved, 3 1/2"-4" black rubber hose located to the right of the engine. I bought some MAF cleaner, sprayed it real good, gently used a q-tip around the resistor, put it all back together and so far, 100 miles later, the light is still out. The engine seems to be running smoother to. I would probably replaced the intake gasket next if that didn't work. Good Luck
you should create a signature for your car. include as many details as you can, engine, year, etc. my 98 does not have a MAF.
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#13 Old 12-19-2011, 08:59 PM
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my turn on P0171 Fuel System Too Lean - Bank 1

Every cold weather season,the code occurs with cold weather.
The code goes away after a couple of days, Comes back again,then goes away. Then its spring time. This has gone on for 2 yaars.

Its cold again, the code came on 3 days ago, it went out today. I fiqure this year i might try to solve it. It did not happen during the first tens of thousands of miles when the car was new, i am thinking some parts need to be replaced with new parts.

To begin with aMAP sensor, does my 2005 Corrola have one?
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#14 Old 12-20-2011, 06:17 AM
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Quote:
Originally Posted by empirefalls View Post
my turn on P0171 Fuel System Too Lean - Bank 1

Every cold weather season,the code occurs with cold weather.
The code goes away after a couple of days, Comes back again,then goes away. Then its spring time. This has gone on for 2 yaars.

Its cold again, the code came on 3 days ago, it went out today. I fiqure this year i might try to solve it. It did not happen during the first tens of thousands of miles when the car was new, i am thinking some parts need to be replaced with new parts.

To begin with aMAP sensor, does my 2005 Corrola have one?
you have a MAF sensor.......read the thread from the top.plenty of info in there for you....do you have an aftermarket airfilter or a cold air intake.....
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#15 Old 12-20-2011, 06:52 AM
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Quote:
Originally Posted by Woodyg View Post
you have a MAF sensor.......read the thread from the top.plenty of info in there for you....do you have an aftermarket airfilter or a cold air intake.....

As in a Fram air filter? Yes. Clean, i replace 2x ayear
"cold air intake." Original

All sensors are original. I have no aftermarket parts. Spark plugs changed 2 years ago with manufacturer recommendation.
I just realized, the fuel filter is orginal and never changed

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Last edited by empirefalls; 12-20-2011 at 06:57 AM. Reason: add info
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