P0171 - System To Lean (bank 1 )

[Joe Cerda]

I too am having the P0171 problem.  I have a completely stock 2000 Celica GT with 95K miles.  The CEL recently came on with error code P0171.  Coincindentaly, this happended about two days after I got it back from the dealership to have a brand new transmission and clutch installed, so I'm wondering if something in the exhaust system is not put back together correctly.

I cleaned the MAFS, cleaned the throttle body and IAC valve, replaced the PCV valve, and visually inspected any vacuum hoses I could without taking anything apart.  I reset the ECU, but the CEL came back shortly.

I then took it back to the dealer who did the transmission work, who said that it is running lean, but only at idle, and that the O2 sensors and MAFS are fine. They think it's an "intake leak", but want to keep it for a day or more to diagnose. 

I'm not ready to give in just yet... I'll try running some injector cleaner, and maybe look into replacing the fuel filter.  If anybody has any new updates, please post them. 

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[jasper]

i am planning to buy this used 2000 Toyota Corolla. The car is great except that the engine light is on and the 171 code Bank 1 appeared per diagnostic check. can you guys advise me if it's ok to buy that car or it's better if i don't acquire it? do you think that is a major problem for me in he future?

i will appreciate your honest advise on this as this is my first experience in buying a car.

[GT4 BOOSTER]

http://www.obd-codes.com/trouble_codes/gen...ygen-sensor.php

[[gato]]

...

Then the light goes off. Comes back on an hour later. I do notice that just before the light comes on that there is a slight hesitation, split second, in the power. I do start to feel these very slight hesitations while drive. They are barely noticeable and the car seems to drive just fine.

...

Hy everybody, my first post :D

Sorry if my enlish is not to good

My father's car (Corolla 2000 1.4vvti) has the same problem, the light on and the slight hesitation in aceleration.

He goes to toyota and they substitute the O2 meter, but the car continues with the same problems.

Once i drive the car and pushed all the shifts to 4000 rpm, and the car starts to get less problems of hesitations, but my father don't acelarate too much.

One more thing, this problems appeared more or less one year later then my fhater buy the car, but happened rarely.

I'm thinking to make a reset to ECU, mainly because of the symptoms that ocure when I drive de car.

One question off topic, to reset ECU? disconnect the negative Battery, wait 5 minutes and press the break pedal?

[][]

[sandymac]

I have a 2000 Avelon. The CE light came on last week. An auto parts store ran the codes and it came up P0171 Bank# too lean. I cleared the light and it came back two days later. Car runs fine and suddenly I'm getting 30 MPG. The best I ever got was 25 MPG before the light came on.

I think I'll put up with the light and enjoy the gas savings.

[obd2guru]

As i have read all the posts i just want to clarify some things that i think people will have some confusion ,as in my experience in diagnostics i have come across this proble a lot of times , but for the diy mechanic is somewhat confusing, as to cleaning the a/f meter,

In new models the airflow meter has 2 main group of sensors incorporated in a single unit , being one the IAT and the other the AIR FLOW METER , the IAT sits on the outside and looks like a big DROP of syrup , cleaning this will make no diference in relation to the code ,

now if you look closely at the unit ,look deeply inside and you will see 2 little grey (car models will differ in color) zener diode "look alike" sensors These are the actual A/F meter components ,These are the ones to clean if you want to get rid of these problem,

[wcottrel]

Hi odb2guru;

thanks for your comments about the difference between the IAT and the air flow sensors. i took the MAFS off the vehicle and saw the IAT so i looked further.

i cleaned the air flow sensors and put everything back together. however, the screens that hold the MAFS in place were close to the head being stripped by a mechanic who hade taken this apart and clean it when i had it in the shop. (he apparently had cleaned the IAT instead of the air flow sensors because my check engine light came back on after i got it back from the shop.

i thought i might replace the screws. are the screws that hold the MAFS in place special screws? are they for sale by toyota or can i buy them anywhere?

thanks

bill

[Preserio]

i have 2001 corolla in canada.

I had very annoy problem with P0171 code :censor:

I just did the same thing with cleaning inside 2 silver wires in the MAF senser. Little did I know I only clean the outside one and i didn't work. so I just clean the inside ones too and freaking worked like new car. Now from ****** to I can start up faster at red lights. I fyou have the same code just use the throtle body cleaner to spray the inside and outside of the sensor. If you don't know what is MAF sensor it's located on the air filter box on the right hand side. only 2 screws holding it.

I hope yours get cleaned up too. Saves gas too :P

[georgeincanada]

I also can confirm that the P0171 (system running too lean) code was caused by an accumulation of crud on the sensors. On my 2001 Corolla the air mass flow sensor is very easy to remove (2 screws) and is very easy to access. To clean the sensor I used brake cleaner which contains isopropanol, heptane and CO2 as propellant. This cleaner, although it's for brakes, doesn't leave any residue and does a fine job of removing the deposits.

In addition to the P0171 code, I noticed also that the car hesitated slightly on acceleration; that hesitation is now gone.

The air mass flow sensor as shown in the photos is probably the same for many Toyota models. These photos were posted on a Toyota 4x4 discussion forum, yet the same sensor is used in my Corolla.

Before cleaning:

After cleaning:

General view of Toyota air mass flow meter.

As I said, I didn't use contact cleaner, I used brake cleaner.

[FJand MR2]

I'm getting P0171 and P0174 codes on my 2000 MR2 Spyder. P0171 is System Bank 1 Lean, P0174 is System Bank 2 lean. If I'm getting both of these codes at the same time, could it mean I have some type of a vaccum leak? I have also read on other forums that there was a recall for the fuel injectors in some of the 2000 Toyotas. Could I have a bad fuel injector? Your thoughts on troubleshooting this problem are appreciated!

Dear MileHighSpyder. I have 2000 MR2 with 87,000 miles, runs great but also got check engine light with trigger codes P0171 and P0174 together. What fixed your MR2?

[sikkim]

Hello Guys,

This thread seems to be old but i am hoping some of you who got this fixed can help me here..

Recently I got the 3 codes - P0171, P1133 and P1135

Any help is appreciated.

Thanks

[GT4 BOOSTER]

http://www.obd-codes.com/p0171

[fullhouse]

the want P0171, P1133 and P1135

but in your link it has P0171 OBD-II Trouble Code only.

these are some of the instruction being said:

A code P0171 may mean that one or more of the following has happened:

* The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.

* There could be a vacuum leak downstream of the MAF sensor.

[john steve]

I am having Toyota innova car.Its model is 2007.Some times my car air contioned is not working,i checked with the gas its also fine.after a couple of 5 mins its working

===============================

john

Foreclosed Homes

[Angel_1977]

Hello, Everyone. :) This is my first time on this site. I have read most of the replies about the Error code PO171. My husband and I first came across this site because of this problem with this code. Since viewing this site, we have replaced both o2 sensors ($200 for the one before the converter and about $100 for the one after from autozone, alot cheaper than from the dealer :) this included shipping because of where we live), we completed a full tune up and replaced the throttle position sensor. The check engine light went off and then after a few trips to my daughters school and just around town the light came back on. Showing the same code.

Our next step is replacing the we MAF sensor ($105) and the temperature sensor ($40). he cheapest replacements of all. This will according to the toyota manual cover everything that this Error code PO171 could be. If anyone has any suggestions or recommendations. They will be appreciated. I just wanted to share our experience with this problem, and maybe help others.

Thanks for your time. :)

[bruce6688]

My car has same code P0171 only, but nothing wrong can be told when I drive my car except check engine light on. I sent my to Toyota dealer, they said thermostat need to be replaced, but I paid $300, still light there. so Toyota will give me no more charge repair my car. then they replaced intake gaskit, still didn't help. finally they replaced one used part MAF sensor to fix my problem. they didn't want me know that, but I still figure out what they did with my car, because first time I guess that part defective and I left mark on it. so I thought this is a ture problem. later on, if somebody drop car let them to repair, be careful to check what part they will put on your car. they really use old part from other car to repair your car. their tech often make mistake to replace wrong parts

[chorse_70]

Finally I'm able to reply to this post!

I bought my 2005 Toyota Corolla a little more then a year ago from the dealership with only 57,000 miles on it. Within about 3 months from the time I bought the car the check engine light came on. I took the car to Autozone to have them pull the code and found out it was p0171 running lean bank 1. The employee for Autozone said it was my o2 sensor in the front of the car on the exhaust manifold. There are 2 o2 sensors on my car (1 on the manifold and 1 on the exhaust itself by the catalytic convertor)he also said it could be the fuel injectors were clogged. He erased the CEL and I decided to go with the cheap possible fix of a fuel injector cleaner called Lucas. Within 3 weeks or so the CEL came back on. I have been told over and over to drive the car with the CEL on and don't worry about it till the car starts running bad but since I worry a lot I decided to get a price on a o2 sensor. For my particular model it's anywhere from $175 to $210. Being the this item is so expensive I decided to keep driving the car the way it was untill I could afford a new one. I told a friend of mine who owns his own shop what was going on and the code p0171. He latter called me to tell me the his mechanics all said that it's not my o2 sensor bit a MAF sensor that's giving that code and that pulling it out and cleaning it would cure the problem. I bought some MAF sensor cleaner and pulled the sensor and cleaned it. I first watched a Youtube video on where it was and how to clean it. One again within 3 to 4 weeks the CEL was on again. I read that if cleaning it didn't do the job then to replace it. The MAF sensor cost $80 so I tried to clean it again first. Within 3 to 4 weeks the CEL came on again. This has got to the point it's driving me crazy! Once again I asked several mechanics and auto part stores what they thought only to get the answer it's my o2 or my MAF. Finally I decided to but a new MAF sensor and pray that took care of the problem. The night before I went to buy one I ran upon this site and noticed one guy who works for Toyota say it was almost always the MAF sensor that caused this code. Another guy put up pictures of what the MAF sensor looks like and what wires to clean. Another guy wrote that cleaning the IAT wires would do nothing and only when I cleaned the sensor wires would it make the CEL from coming back on. I saw the pictures that were on this site of where my sensor wires are on my MAF sensor and realized I've never cleaned those wires and every time I've only cleaned the IAT wires. I pulled the MAF again and have now cleaned those sensor wires and my fingers are crossed again. My thought is that if the CEL doesn't come on within a month or so that I finally fixed it. Remember the MAF sensor is on the air flow box around the air filter housing and has 2 screws in it and a plug. Pull this and clean those wires deep indide it and hopefully you'll solve your problem.

[igeo]

Hi All,

This is my first post. I'd like to share with you some of my experiences with the infamous P0171 code.

My 2001 corolla with 70k miles was running beautiflly, but roughly 6 months ago everything started to go downhill.

- First, I noticed was my fuel efficiency, it went from consistent a 37+mpg highway to low 30s.

- Then, I noticed that my engine had a hard time accelerating. When I hit about 2500 rpm, I would hear engine rattle/ping. The noise become so loud that I am afraid to go over 75mph, but as soon as I slow down my car was back to normal.

- The biggest problem started about a month ago, when the engine fails to cold start properly. Instead of starting and shooting up to 2000rpm and settling down to 1500rpm, it starts and immediately drops to 500-800 rpm, making a sound as if it is having trouble turning the crank. It would take a long time before engine get over 1200rpm. Hot start wasn't as big of an issue, but it definitely wasn't right.

- The last straw came when the engine light came on, and boom, the infamous P0171 code.

Here are the steps I took to diagnose my problem.

- First, I tried changing gas stations(ARCO, Valero, Shell, Chevron, 76). I even tried premium gas as part of my experiment. I don't think it was the cause of the problem, but Arco/Valero gas station were definitely giving me some funky noises and *****ty fuel efficiency. This is confirmed with a local mechanic who told me of bad gas station practices, so I'd avoid those Arco/Valero gas stations from now on.

- Second, just to rule out possible problems. I changed my spark plugs to new OEM plugs. The old ones came out to be a bit white(temperature too high), but it wasn't damaged at all. Obviously this didn't fix the problem either.

- Third, I read on many many forums that the air intake path could be a problem. P0171 code further confirmed it. I swapped out my old air filter and cleaned the MAF. Maybe I experienced a 5% improvement, but it definitely wasn't a life changing experience like some of other readers.

- But I kept on looking, and this is when I stumbled acorss this forum. It caught my eyes that some of you guys had improperly cleaned the MAF. Thank you GEORGEINCANADA so much for your posted pictures. I wouldn't have caught these mistakes myself.

After I correctly cleaned my MAF, the first time I stepped on the engine my car JUMPED. I haven't experienced this much power for so long, this is going to require me to change my style of driving(okay, maybe a bit exaggerated). I'm also happy to report that cold start problem is completely gone, and I easily sped up to 80 on the highway without any issues.

As my final words, I'd like to thank everyone for sharing your expertise and experiences. This would have been a $500 job at the dealers, but thanks to all of you I did it for practically nothing and got a huge sense of accomplishment out of it. Hopefully my experiences would help someone else in return.

Keep up the great work gearheads. Good luck on your next projects!

[highwaysman]

I have a corolla 1.4vvti, 76k on the clock (X reg 2000) get 42 mpg if driven steady, run it on Shell V Power as other fuels affect economy dramatically. I have got to thank georgeincanada for the exceptional post. Got this car off my Dad and has always pinked especially at 70 - 80 mph and pulling up hill. It would stall on set off if revs not kept above 2000, would be underpowered when running air con. Engine management light has been on since Feb this year. Read Georgeincanada's post and immediately went to my car and took out the air mass flow meter, noticed the sensors were black and cleaned them with a can of windscreen cleaner ( aerosol type, high alcohol content and guaranteed to leave no residue) and a very fine cloth. I can't believe what difference this has made, no more pinking, now only require low revs on set off, 600 rpm on tick over, no loss of power when air con running, takes off a lot quicker and runs very smooth. I would have never guessed something so insignificant could make such a big difference and to top it all after 50 miles the engine management light went out, total outlay £0 and about 10 minuets of my time, can't get better than that. Just waiting to see how my economy will be effected (poss not that good at the moment as I keep pushing my right foot down to test for pinking as I can't make it do it now) Keep up the good Work George and if your ever in the UK I owe you a Beer or two.

Regards

Highwaysman

P.S. Does my Toyota have a timing chain or a belt, I’m 95% sure it’s a chain but the dealer confused me by saying it was a belt?? As I can gather from this site diesels have the belt and petrol have the chain, is this correct?

[GL645]

My problem with car shake at stop/idle RESOLVED. Here's my story, and maybe it could help someone else (this site has helped me and I want to contribute).

I own a 2001 Toyota Celica GT with about 114,000 miles, and the check engine light came on about 3 months ago. I never took it into the shop because I was still able to drive it and nothing seems to be wrong with it. Then about a month ago, I started to notice my car would shake and appears to want to turn off when I'm idling at the stop light. The RPM would drop and the car shakes then it goes back up. That's when I realize maybe it has something to do with the check engine light. I purchased a hand held code reader and it indicated a P0171 code (fuel too lean). So I went online to see if anyone else have this same experience and found that most people think it's the MAF sensor - mostly needed cleaning. So I checked under the hood for the MAF sensor that is located right after the air filter. Well, what happened next was I guess you can say "by accident". I noticed the air filter cover was not installed properly by the people who last serviced my car - one of the quick oil change places. This Celica has a really tight air filter area, and in the past the service techs don't know how to put cover back properly. (Lately I've been telling them NOT to check my air filter since I can check and change the air filter myself. Well looks like they went ahead and tried to look at the air filter and couldn't spend the time to reinstall it properly.) So I opened it up the cover and while I was in there I changed the air filter. Then I reinstalled the air filter cover securely as it should. Then I turned OFF the check engine light. I didn't do anything with the MAF sensor at this point.

It's been a week now and the check engine light hasn't come back and the car does NOT shake or drop the RPM during a stop light or at idle anymore. I might have been lucky that this problem (P0171 code) was resolved this easily, but I think it's a fast check to make sure your air filter cover is on securely if you have the same issues as my car. Good luck.

[chorse_70]

Well I wanted everyone to know I changed my gas cap,MAF sensor and o2 sensor pre catalytic and even ran Lucas through my car to clean out fuel injectors and of course the dreaded p0171 running lean bank 1 code is still showing up and my CEL is on once again! I've even pulled the ECU fuse to clear the code. We sprayed cleaner on the intake to see if it sucked it in so we could know if it was a leaking intake gasket but nothing happened? I'm at wits end now. I know I got the right o2 because I compared them and the right MAF as well. I've become very angry with this issue. Any more suggestions?

[1997RedCamry]

4 cyl '97 Camry with the P0171 error code. Does a 4 cyl have a MAF sensor? If so, where is it? I can't find one.

I cleared the error code with my code reader. A couple of days later I get a gas smell, look at the dash and the check engine light is back on.

The car can go into periods of poor acceleration, hesitation, lurching acceleration, seeming like it wants to stall, etc.

thanks

[Gear_Chick]

Jeffrenee,

My truck was doing that too. One thing I discovered is that usually if your system is too lean it's the O2 sensor and something else. The first thing I would check is a leak in a vacuum seal somewhere. You can usually hear it if it's bad enough to trigger the light.

Do you have any other codes too? If you get something about your cylinders / valve clearance and a blinking check engine light I would recommend checking the intake hose. And if you have something about the throttle, I would recommend the PCV, assuming it's spring-loaded. These are some things that could make it too lean if the O2 sensor is broken.

[chorse_70]

Ha In my case I took my car to the local Autozone who erased the code yet again and it took like 4 or 5 weeks but it's back on! I'm replacing yet again the same O2 sensor by returning the one I bought and getting a different one. I was told it may be bad even though new? I doubt it though. Already replaced MAF sensor and used Lucas to clean out fuel Injectors. If this doesn't work now I will be getting the diagnostics check and pray that tells me what's really wrong with my car.

[Mike1844]

I have a 2001 4Runner. I just cleared my P0171 code by replacing the fuel filter. It appears that it was clogged.

The code cleared immediately and it has since passed an emissions check.