ravengotu

Hi guys...thanks lexmex for helping me out....i went back to autozone and it says PO 171 bank 1 the guy now says it is an o2 sensor......can i check this or what..plz help my LEX..IT is sick.....

Lexmex

P0171 is defined as System too Lean (Fuel Trim)

This code is by far the most common error that occurs on my RX and from what I can tell in this forum, it is also the most common. I actually take a lot of delight in getting a lean error (more air than the amount of fuel) at my altitude, but no one else should unless they do radical air modifications.

The problem areas can be the following:

-Air intake hose loose. There is one on the back of your airbox that might be the main one and it could be corroded or have holes or simply not be connected tight enough

-Engine coolant temperature sensor (doubtful) as other things might creep up that you haven't yet faced

-Fuel line pressure- use of a fuel system cleaner woud be enough here at first (related to fuel pump, fuel line and filter)

-Injector blockage- use one can of Techron with Premium gas on half a tank (I have actually one this on a 1/4 tank with no issues)

-MAF sensor (that little sensor on the tube going off the top of the air box. Remove and clean it with electrical contacts cleaner (red diode and there are some resistors that you have to clean by looking inside it), also pull the EFI fuse (easy way to reset the CEL). An unclean or even a faulty MAF will result in repeated CEL errors and I had this issue once and it really drove me nuts until I cleaned it.

-O2 sensor- I can't rule this out, but if this error keeps creeping up and is not related to one of the hoses then this is the most likely suspect.

-Spark plugs (doubtful though listed in the service manual)- if you have bad plugs, you probably would be running a little bit richer.

SteveH

i had similar problem with check engine light and error code, I cleaned the MAF sensor, right behind air box , remove two screws unit lifts out clean with electronic cleaner from Auto Zone reinstall clear check engine indicator, $5 fix instead of $123 part and labor from dealers

ravengotu

I just got me a can of CRC cleaner...took it apart and gave it some squirts ...and now all is well...Im so happy it is running well thanks a millon

tracyinva

I just bought a used lexus and got some code..bank 1..it was the o2 sensor.

ravengotu

Did you go to autozone..they will let you use theres to read code.....Buy a can of electronic cleaner CRC and remove two screws and clean MAP sensor.and reset fuse and give it a try... Worked for me and still going good

tracyinva

I have had my '99 rx 300 for 4 days. I bought it from a used car dealership.. They replaced the o2 sensor..engine light came on again..now they think its the air flow sensor.. I am beginning to regret this purchase

Lexmex

If the dealer says it is a MAF sensor, make them pay for it if they are wrong. I almost never think the O2 sensor is the problem with this particular code and I have thrown some wild stuff in the tank and imagine all that bad air going through mine. There aren't many more realistic things after the MAF sensor.

It could be a buildup of gunk issue on that sensor (a square sensor with two screws in it) located in the tube just after your air box. Easy to remove and see if there is any accumulation on the red diode (though I doubt it on the little threads inside).

tracyinva

I have no idea why they replace the o2 sensor. They are not certified lexus mechanics...just a used car dealer. Othern than that the cars runs great. I just did mobil 1 oil changed..replace the air filter also and put some fuel injector cleaner in it. I hope this fixes it . They are paying for both o2 and maf . I will let you know how it goes. Thanks for the advice. I probably will pick the car back up tomorrow.

tracyinva

I have been to the used car dealership 4 times so far.. the engine light came on AGAIN today with po171 bank 1 system too lean. I have no idea whats wrong it. I just bought the car last weekend. I have been to the dealership 4x to get this crap fixed. Does anyone else have any ideas what to do? They won't take the car back.I am stuck with a crappy car they wont fix right. They already replaced the o2 sensor.

VVT-i

P0171 is system too lean and like everybody else said it's an air flow meter problem. They said they replaced the O2 sensor,but the RX300 have 2 AF( air/fuel ratio sensor) on the exhaust manifold and one O2 sensor( after the cat).
You need to tell the used car dealer to look at the fuel trim data on the scan tool. The short term fuel trim and the long term fuel trim combine have to be close to +/- 0%. A bad air flow meter will shows, for example

Short term fuel trim -3%

Long term fuel trim +43%

Total fuel trim +40%

This reading show a way out of range.

I think they just clear the code and hope it will goes away or you will go away to the Lexus dealership.

anulex

Had my MAF sensors replaced 2x and fuel air sensor one. dont care. cost me nothing

Lexmex

The list I posted earlier is pretty much the entire deal behind the P0171 error code.

One other thing comes to mind. I have known not only with my RX, but with some other OBDII vehicles that even when you are 100% sure you replaced the exact piece that was the source of the problem, the information in the car's ECM that originally tripped the error is still there.

I would recommend you pull the negative battery cable off for about 30 minutes (1 hour to be absolutely sure no juice in any capacitor) and then reattach and drive the vehicle. This should clear any old data.

BTW, I also bought my 99 RX used in Virginia.

tracyinva

I tried to disconnect the battery cables when the orginally said they fixed it and the error light still came back on. I will see if i can figure it out. I think I go maybe 15 miles before the light comes on.

Thanks for message.

Lexmex

If everything feels like it is running normally is has to be something extremely small like a hole in some hose or somewhere along the intake line.

How soon does this error up pop after you start up the vehicle?