Well heres the deal, i was heading from Kansas City to my school in Pittsburg, about 120 miles and while mergine onto the highway and giving her all she's got my Cel flipped on. This is the exact same scenario that it was the last time it came on. It's a 98 taco 2.7l w/only 70k on it so it should not be having these problems. I pulled over, everyting seemed cool and since i didn't have an option, continued to drive home to pitt. Today i went to Auto Zone and they read it for free and the code it threw is P0171 "Bank 1 Running Lean" . First of all my thoughts, oh f*ck i'm running lean, had it said rich i'd not sweat as much but lean = melting pistons. What also confused me was "bank 1" if it's a 4cyl what do they mean by bank 1, it hought that was only for v6's and v8's. Anyways though, i'm a broke college student and cannot figure out what i should do. Should i reset the ecu and see if the code goes away? However this is the 2nd time it's happened therefore probably time to do something. What am i looking at here. Thank you immensly for your time and help.
Jamie

it could be an o2 sensor screwing with the computer and sending that code

i could almost bet if that was the case then the o2 sensor closer to the engine is going to be bad

agreed...although I'm not familiar with the 2.7 tacomas...if it has 2 O2 sensors and you're getting a bank one lean code, then one of the two O2 sensors has failed. Bank one should be the one located closest to the engine if that ends up being the case. Good luck.

P.S. In the meantime, try disconnecting them both, that way it should fail rich, your gas mileage will suck, but at least you won't be toasting your slugs. <img src="/forums/images/graemlins/smile.gif" alt="" />

Something else I just thought of....it might not be an O2 sensor failure at all...you could actually have a lean condition as a result of a clogged or malfunctioning fuel injector. Have you noticed a power loss? This could end up being a complicated troubleshooting ordeal. <img src="/forums/images/graemlins/confused.gif" alt="" />

Just a thought while you are looking for an answer. Are you running stock toyota spark plugs? My T100 started throwing codes when I had some bosch plugs in. Replaced them with some toyota plugs and no more codes.

P0171 code does indeed indicate system too lean (bank 1). The O2 sensor nearest the engine on the exhaust is the bank 1 sensor. Here is a list of the many things that can cause this.


Air induction system

Injector blockage

Mass air flow meter

Engine coolant temp. sensor

Fuel pressure

Open or short in A/F sensor (bank 1 sensor 1) circuit

A/F sensor (bank 1 sensor 1)

PCV valve and hose

PCV hose connection

EFI main relay

A/F sensor heater and relay circuit

But don't forget to think simple first. The code says it is running lean...so did you run it out of gas recently? When was the fuel filter changed last? Check it real good for bad or disconnected vaccum lines to include the PCV valve and hose. Check your air induction system for leaks allowing air to enter after the Mass Air Flow Meter. Any in depth trouble shooting requires the shop manual and an OBDII computer or at least a multimeter that reads in mili-volts. Good luck with it, let us know if ya have any other questions.

I have a 95 2.7. When I had that code it turned out to be and exhaust leak at the cat. I had just finished installing an LC header and the new gasket was the wrong one. I put the old one on until I had a chance to go to the dealer. It did'nt last. check the simple stuff first.

Read this article for an explanation of the cause (and the fix) for this problem occurring under almost identifical circumstances

Clean the MAF sensor... The MAF sensor used in your vintage of vehicle is prone to accumulation of contaminates on the sensor that causes it to undermeasure the amount of incoming air under acceleration conditions you mentioned.

The Federal requirements for OBDII systems standardizes the naming of the error codes.. Bank 1 would be the left cylinder bank and Bank 2 would be the right bank on V8 engines equipped with dual left and right catalytic converters.

Single catalytic vehicle systems will always use the left bank or bank 1 error codes..

For more on OBDII engine management systems check this out..

Well I took off the intake, cleaned the t.b. and the MAF sensor w/some electronic cleaner then reset the ecu and the code has gone away, but it seems like it only comes on when i'm merging onto the highway at highspeeds at major wide open throttle. I have never done the fuel filter, i guess that could be clogging up but i dont have any other symptoms of a fuel delivery problem at all. Vacuum leak very possible but how do i check for that? also it does have the stock Yota plugs in it w/less that 10k on them.

Have you gone out and tried to duplicate the problem after cleaning the MAF sensor? You may have cured it already.