P0171 - System To Lean (bank 1 )

[jeffrenee]

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)

[jeffrenee]

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

[MyV6Flys]

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??

[speedyts49]

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

[hydrae]

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

[speedyts49]

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!

[phasor]

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.

[MyV6Flys]

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.

[phasor]

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?

[phasor]

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.

[MileHighSpyder]

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!

[speedyts49]

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

[jto]

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...

[phasor]

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

[pgsandiego]

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!

[TZ_2003]

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.

[MyV6Flys]

p1133 = air/fuel sensor circute slow to respond.

bank 1

[ender21014]

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.

[4thgenCamryv6]

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.

[bxin]

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!

[ssmall]

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

[ssmall]

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.

[Kanadakid]

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

[Matt007]

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.

[GT4 BOOSTER]

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