pdyebrasil

So yesterday I did a few maintenance items... I changed out the spark plugs to OEM Densos I got from the dealer, I cleaned the throttle body with some throttle body cleaner, and then cleaned the MAF with MAF cleaner. Then I disconnected the negative battery cable to reset the ECU, and then I started her up and she ran great! I mean, she was running good before, but now it just purrs...

So anyway, I drove around yesterday with no problems, but then today I am cruising around and my check engine light comes on. Odd I thought since it didn't come on before. So I ran down to Checkers and they pulled the code, and it said that Bank one was running lean. So apparently the forward o2 sensor was sensing that it was running lean. I just had them clear it and it hasn't come back on yet.

Anyway, my question is: Does this happen normally or occasionally? Or is this a sign that I may need to replace my o2 sensors in the near future? I'm not too worried about it since she's runnin' great, but just wanting to dig a little into this to see what could be going on...

toytech76

What code was it? The code p0171 is fuel trim malfuntion (bank 1) 99% of the time relates to a bad/dirty MAF. Alot of people automatically think this means its a bad 02 sensor. Was it this code or an actual o2 sensor code?

pdyebrasil

Thanks for the reply man... I'm pretty sure that was the code that it pulled up. I guess that makes sense since I did mess with the MAF. Although I cleaned it (so it's not dirty) and the wires were in good shape. The light hasn't come back on since I had it cleared, so I'm guessing (and hoping) that it was just a one-time thing.

Fink

Unless you are noticing a drop in performance then I wouldn't blame your O2 sensor.

In my experience, you will notice something wrong before it trips a CEL.

I think you did the right thing, clear it and drive it some more.
If it trips again, go back and get the actual code that it is throwing and post back up.

Fink

BigBallsMcFalls

this.


when it is the front O2 sensor bad, it will make system report lean.

then you will actually start running rich as it tries to compensate, and get sooty exhaust and crappy mileage


if mileage is OK and exhaust is clean, then the code is likely not the front 02 sensor, but no guarantees

it depends on how long you removed power from the ecu

you may just need to keep driving while it generates new long term maps

or
power-cycle the ecu 15 minutes. guaranteed to wipe it out to factory

icerunner

YO,
Due to the fact that one has to pull quite a bit of components off of the engine to get to all the plugs you likely missed a vacume line or a plug is loose...sounds exactly like when I changed the plugs and one of the spark plug connectors was not reconnected by me... my engine died with a registered code....
OH YEA the only other thing is that you may need to clear the codes out may be an old signal before the change? ....Maybe also a loose vacume line? check ALL the air handler ducting for tight fit if that is loose you'll get a code...Later

pdyebrasil

Hey guys,

So after I got the code cleared out it ran for about 15 miles and then the code came back on. So I pulled the EFI fuse to clear the computer. After about 20 minutes I went back out and started it and it ran pretty crappy, but no check engine light. After I let it run for a while and drove it around it started re-learning and it ran a lot better. Then it popped up with the check engine light again. I then went on a trip (about 600 miles round trip) and it ran fine and I got fairly decent gas mileage (around 19 mpg w/ lift and tires) and then I went down to Checkers and they pulled the code: "PO171: System too lean (Bank 1)". So I guess that it must be the MAF. The thing that kills me is that I cleaned it w/ MAF cleaner and I NEVER touched the wires. Looking down in there they seem to still be intact. What do ya'll think?

Fink

You will not be able to tell by looking at the internals of the MAF.
They are too sensitive for you to notice any damage.

ROOFGOOF (member on here) just had this same problem and a new MAF sensor from Toyota fixed it.

Fink

ROOFGOOF

Yeah ! I just went through that too.... Get a new MAF sensor. You should be able to get one for under 130 with shipping.

I haven't gone through my whole tank of fuel yet, but at this rate, my new MAF got me at least 1-2 mpg more than I was getting before.

pdyebrasil

Hey guys

I feel a little stupid, but relieved as well... I've been living with the engine light and looking at my options (new MAF $500, or convert to '99+ for less) and I was just checking around my engine looking for stuff and I noticed that there was a nice round hole up where the intake tube meets the throttle body with nothin in it! So I look around and at first could not for the life of me find any unattached hoses, so I figured that I must have lost it. But I went in and popped the hood on my sister's 99 4Runner to see if hers looked the same and what it was attached to, and sure enough I found it

Anyway, I haven't gotten the light cleared to see if it'll come back on yet, but that totally makes sense that it would trigger that code if more air was getting in than the MAF said was getting in, of course it'd run lean...

Thanks for all of your help!!!

icerunner

Chalk one up for the Icerunner Boys!!!!
Nice catch and you saved your self 500.00 on a new MAF!!
later

ms_betty

I think I am having this same problem.

My not quite week old truck lit up the CEL as I accelerated up a hill about 15 minutes into my drive. I called the dealer I bought it from and the sales guy admitted that it had happened before and they weren't sure what it was, but since it happened again they thought they knew it for sure now.

He said something about O2 sensor, and then accused me of not putting my gas cap on right.... I made an appointment for Wednesday.. and I assume that I don't have to pay, since they were aware of a problem and did not disclose it.

I also took it to my mechanic to check the code and he said it would have come up with an emissions code for the O2 sensor or gas cap not on tight... he said it was something to do with the mass air flow. ( which I had not heard of before.. I have of course been reading up on here and I love all the great info I get from all of you! If the dealer won't fix it for free, I'll take it back to my mechanic who does good work ,and is really fairly priced.