My check engine light came on the other day while I was driving on the highway. I called a couple shops and they said check the gas cap. The gas cap was fine so I took my 2000 4 runner into the shop. Two visits, one new o2 sensor and $350 bucks later the CEL came on again after driving on the highway for about 15 minutes.

A lot of threads recommend cleaning the MAF. If that doesn't work anybody have any suggestions.

Oh yeah, the error code from the OBDCII was P0171 - System to Lean (Bank 1)

I cleaned the MAF and cleared the light by pulling the Neg bat terminal. I drove for about 2 weeks including about 100 highway miles with no light and then it came on again the other day. I am also noticing poor gas mileage. I am going to replace the MAF and see if that clears the problem.

I am concerned because I am driving from Seattle to FLA in 3 weeks and don't want to see the CEL in the middle of BFN.

If anybody has any ideas please let me know.

Thanks;
Jeff

book show p0171 system adaptive fuel too lean.

So I would have to guess o2 or maybe a dirty fuel filter not letting enough get by, setting the fuel too lean.

Hope that helps??

I recently had my check engine light come on so I bought a OBD 2 scanner and got the same code, P0171. I had recently changed back to a OEM air filter from a K&N and am thinking that may have had something to do with the lean code fault. Any thought on this?
Also I do not know what a MAF is and would like to know so that I might clean mine too just in case.
tom
'96 tacoma 2wd 2.4L manual

I have a 2000 corolla and have MIL on with the code P0171. Any advice would be helpful.

1. I am first planning to add fuel additive to see if that helps.
2. If that doesn't help I am planning to clean/change Fuel pump/filter assy.

Any other suggestions?

Thanks

My fault was caused by a air leak when I knocked off a vaccum hose from the canester while replacing a heater hose. I heard the whoosh and found the lek.
Good luck!

2000 Avalon

My Check Engine Light Came on while driving on the highway. The Toyota dealership said it was code P0171 -- Fuel Too Lean. The technician was a nice guy and he explained to me that the service manual lists a number of things but based on his experience he would narrow it down to A/F sensors. There are two sensors in the vehicle Bank 1 & Bank 2 Sensors. We drove around and recorded the voltages for the sensors -- 3.0 Volts during idle, above 3.8 Volts accelerating above 2500 RPM, below 2.5 Volts while driving above 25 MPH and tapping the gas. The readings were not consistent all the time between the sensors. We couldnot isolate between the sensors and I did not want him to guess. Each sensor costs approx. $300 and I can't afford to replace them both. So, I had him clear the code for $25.00 and so far the CEL has not come back (I have only driven approximately 100 Miles). Does an avalon have a MAF sensor, is that cheaper to replace? The service manual at the dealership did not mention any such sensor.

1997-1999 Avalons do, so I would guess yours does. It sends information to the computer about air coming into the motor. If it is sending wrong info it could be it.....I'm not saying I believe it's it, just that it could be.

Just as an update, I have driven 500 Miles since clearing the CEL light and it has not come back on yet. I have not changed any sensors. Could the CEL be a fluke?

MY CEL came on last saturday (650 miles later). The DRB at Autozone indicates it as P0171 (as expected). Looks like I will have to change the A/F sensors. Any suggestions are appreciated.

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!

Mine was a vacuum hose I had knocked off doing some preventitive maintanance. If you've do anything to the engine lately I would retrace my steps to see if it was caused by something I had done.
I am not sure about the injectors.
tom

As I read it from my buddy's diagnostic reader, error P0171 was ok to drive. It was funny that the car's O2 readings didn't fluctuate while accelerating or decelerating when we did the test.

It's my mom's car I'm working on. She doesn't drive too fast or hard. She only drives in the city too. I gassed up her car and put some cheap/discount brand gas in it.

I think it might have been clogged up or something. As I left my buddy's house I floored the gas pedal and some smoke came out the back. Reset the switch (disconnect neg.term.)
and it hasn't come back. Do A/F sensors and O2 sensors get clogged?

Next long trip I take, I'll take my mom's car and use the Toyota brand injector cleaner. They suggest you run the tank of fuel and cleaner within a week or it will eat fuel lines.

So far it hasn't come back. I'll post if it does...

I am still driving with CEL ON (over 600 Miles now). The funny thing is that with p0171 code, my Mileage went up from 23-24 Miles per Gallon to 25-26 Miles per Gallon. I donot feel any difference in driving performance. I have decided to tolerate the CEL and continue observing my mileage. As I understand that the A/F Sensors are placed to meet US emission standards. I would think that better mileage would mean better emission....

Am I hurting the car in anyway by doing this?

2000 Avalon

My CEL has been on 40K miles with no problems. I recently went by an Autozone and borrowed a OBDII reader and used it to clear the codes (sensor one bank one). Its been a few days and the CEL hasnt came on!

Thank you guys for posting this. I'm having the same problem with my wife's Camry 97 LE. I'm getting both the P0171 and the P1133. Please keep this post updated as I'm in much need for help on this topic.

p1133 = air/fuel sensor circute slow to respond.
bank 1

I have a 2001 corolla. My check engine light came on several months ago. The last time my light was on it was because of the gas cap so I just pulled the fuse and reset the light. It came back on anyway so after a few weeks I took it to the shop and they said it was an error code of P0171. They suspected it was my mass airflow sensor and told be they could try to clean for over $80 or get a new one for about $140. Instead I went home and looked at the sensor myself. It came off easily and had an obvious dirty part of it. There was an amber colored plastic thing that was really dirty so I cleaned it. Unfortunately this didn't fix the check engine light. I drove with it on for a few months and several thousand miles with pretty much no problems. Until recently, the engine started having trouble when I first started it up. I took the sensor out again and looked at it more carefully and realized I had missed some wires inside of the plastic tube like part of the sensor. After putting it back in and resetting my check engine light, the car worked great! This was awesome because it was such an easy thing to do once I realized what I had to clean.

I can almost guarantee you that your PO171 code is because of a bad Mass Air Flow Sensor (MAF). I work at a Toyota dealership and we see this problem alot and 99 times out of 100 it is a bad MAF. Hope this helps.

SOS!

Camry 98 LE 4cly (In California)

The ECL was on on rmonth ago. The Smog check failed becasue of this. the error code was p1133. I continue driving it and the light went off after 200 miles. I knwo the computer in the car has a buffer to rememebr everyhting, so I kept driving for another 2 weeks to make sure the old record got overwritten.

500 miles past in last 2 week, today I went to re-do the smog check. the p1133 code is gone. But OBD II failed agian becasue of a new code - p0171 (system to lean). So frustrated!

What does this mean? Does this mean I still have to change the O2 sensor? (It's damn expensive -- $350 parts + $60 labor). Or, does this mean If I drive more it can be recovered? Or Is there any way to reset the computer?

The DMV renew is due in a week. I feel so bad now... Your help/suggestions will be hightly appreciated!

I've been having the same problem as all of you. Similar story. 97 Camry. The check engine light came on about two years ago and Toyota replaced the MAF sensor as it was under warranty.

Three months ago the light comes on, I bring it in and they find code P0171 (lean Condition) Freeze fame shows very high trim values. Check that sensor is latest part. Sensor reacts normal to spike and active tests. Cleans MAP inlet filter and road tested. Trim display is now normal.. They note I have an "early ECU" compter.

I get the car back and after a few week that dam light comes back on. I buy some fuel injector cleaner and disconnect the battery to clear the light. Drive for a month then the light comes back on. Disconnect the battery again.

I take it into get smogged and it fails. I take it back to the dealership and get a full service for 105k. My disconnecting the battery had left no codes to refer to. While in line to pay, someone else was having both A/F sensor and the computer replaced - under warranty.....some coincidence.

I go back and am able to pass smog. Two weeks later the light comes on again. I do nothing this time but drive around with the light on for about a week and a half.
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.

I am bringing in the car for the last time to Toyota. With all that I am reading, I think there is a major manufacturing defect in the air/fuel sensors and the computers that they are not be honest about. I'll follow up and let you know what happens

OK here is my follow up to my previous message

This A/F sensor and computer problem is widespread. Toyota probably does not want to admit it. There probably is a malfuction in the match up between the computer and the sensor (feedback loop) that is preventing the air and fuel ratio to be mixed properly. I would also venture to speculate that this problem involves other Toyota products other than Camry, that use this same subsystem for fuel delivery.

I have to say that the dealership where I take my car was very fair and replaced both the A/F sensor and computer. It turns out that the 97 Camrys have an old version computer that is related to the problem. When I spoke with the master mechanic he told me that after taling with the factory, Toyota's recommended fix was to replace both the sensor and computer (over a $1000 in parts alone). Much appreciated was that he got the parts to be covered by Toyota and I just had to pay for the labor only. When this problem first occured I was under 100k but am now at 104k. This was the third time I had brought the car in and had already spent over $300 in labor.

While I was waiting in line again the service person at the front desk was on the phone describing to the customer that they had a check engine light on with a lean condition, and that they were going to try to clean the A/F sensor........"Yes maam.... that would account for the split second hesitation in power..........

The master mechanic said that one of the other mechanics had my same car (97 Camry) and he too had the exact same problem - hesitation in power, followed by check engine light, followed by lean condition codes. Also said that replacement of the computer and sensor resolved the check engine light from coming on but he still gets that split second hesitation in power.

Notes from the service write up: Code P0171 (system too lean) code P1135 (A/F Sensor heater circuit malfunction bank 1, sensor 1). Tech tested A/F sensor on scan tool and sensor is not responding to lean command. Tech prelaced ECU and A/F sensor.

Hope this information helps. This might end up in the news at some point as a product recall due to defective design.

ender above has the goods on the 171 bank one code. I too missed the internal wires inside the MAF sensor. Now I know !!!

saved me some bucks on this gig !!


Kid

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.

http://www.obd-codes.com/trouble_codes/generic/p0171.php

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.

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

Hy everybody, my first post

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?

[][]

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.

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,

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

i have 2001 corolla in canada.
I had very annoy problem with P0171 code
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 [COLOR=red]

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.

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?

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

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

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.

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

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.

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

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.

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!

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?