Cant get rid of P0174 code?

i have a 2008 Tacoma with 120k miles. recently got a p0174 CODE, code said sysem to lean bank 2. changed the oxygen sensor on the passenger side and reset the light but it came back on after a few miles. changed the MAF and air filter and reset the light but same thing, light came back on after few miles. idk what else it could be. i always use 93 octane from BP so not sure it could be the fuel. i did notice the truck idles a bit rough, you can feel it when your sitting inside the truck. the rpm stays still but theres a slight rough idle. truck doesnt try to shut off or anything. anyone have any ideas? im kinda lost here

 

Look for an intake leak at that bank

 

I thought bank 2 was driver side. Double check that.

 

Yup, bank 2, driver side. Ok OP, swap sensors, or just have new on both sides with your mileage would be best.

 

It crossed my mind that i might have did the wrong side, but a local mechanic said it was passenger so i went with it. thank you for clearing it up, i will change it today and let you guys know what happens

 

Good luck

 

system too lean means AIR FUEL sensor not the O2 sensor
not the one highlighted in yellow, but the same side

a/f detect lean or rich...
o2 just checks cat efficiency and cannot blow a p0174 code

be sure you swapped the front A/F sensor, right ? and it is a/f not an o2 sensor

toyota is extremely fussy that be an OEM part as well.


aftermarkets work for about 3 months then fail the ecu checks

 

You're probably wasting your money on 93 octane... Replace the A/F sensor and try regular gas, you'll save a lot and then you can spend more on truck upgrades!

 

What Toyota refers to as the Air Fuel Ratio sensor is generally called a wideband O2 sensor in most automobile technical publication--it is also what NTK, the inventor of same called them. Most parts houses call both wideband (front, upstream, pre-cat) and narrowband (rear, downstream, post-cat) O2 sensors "oxygen sensors" so it's important to make sure you order "front" or "rear", "upstream" or "downstream" as appropriate...

 

I would look for a vacuum leak before buying any more sensors. I work at a Ford dealership, but usually when it gives that code, it's a vacuum leak, or a dirty MAF. It would help to be able to see the fuel trims when you're dealing with rich or lean codes.

 

You're sucking air somewhere after the maf sensor. Check around the throttle body i.e. hose clamps and such...

 

Intake leaks after the MAF generally affect both banks, though anything is possible.

Exhaust leaks upstream or near the sensor can also cause a false lean indication as the trailing end of an exhaust gas pulse is at less than ambient pressure--thIs can suck air into the exhaust and make it appear lean. I have also heard of loose exhaust manifolds, or with leaking gaskets, causing this--but have never run into it myself...

 

120,000 miles is average how far the a/f can last. they do wear out.

 

have you chk'd your fuel pressure?

 

MAF sensor would affect both banks as well as fuel pressure, to properly diagnose before "shot-gunning" parts at it you need to look at freeze frame data to see what conditions the engine was under when the code set. Monitoring fuel trims would also be helpful, if the fuel trims go lean at cruise you have a fuel delivery problem on that bank (injectors plugged), if they go lean at idle, you have a vacuum leak (more then likely). Also, the rear O2 sensor can cause the A/F ratio sensor to skew lean. A partially plugged catalytic converter can cause a lean condition on just one bank as well, but usually the other bank gets driven slightly rich (P0172, P0175). The PCV and purge solenoid hoses are on that bank, check them for leaks. Let us know what you find.

 

Just thought i'd give you guys an update on the situation
Finally fixed the problem. it was the O2 sensor that caused the check engine light and the rough idle. Bank 2 was the driver side, and it was a dealer part only. luckily i got a shop discount so it came out to $135 for the sensor. replaced it, and cleared the code. drove close to 100 miles so far, no light and it idles smoothly now.

 

For future reference RockAuto has the upstream sensors; Bosch, Denso, Delphi, NTK and Walker--$107 to $137 plus shipping, so $135 is a good price from a dealer...

 

So was this an air fuel ratio sensor or o2 sensor problem?

 

Different terminology for the same component--though arguably wideband O2 sensors might be better called "air fuel ratio sensors"...