P0171 and P0174 codes - lean condition?

[mooch91]

Hi all,

Just started getting these two codes on my 2006 4runner, 225K miles, V6.

I've read a number of threads here which point to apparent lean condition - too much air or not enough fuel.

I'm also using this as an opportunity to learn more about diagnostics with a scanner.

I did not capture freeze-frame data when these codes occurred; will need to do so next time it happens to understand some of the other conditions when it sets.

When I review data at idle, things generally look ok. LTFT and STFT are +/- a few %. A/F lambdas showing 1. MAF is about 0.5 lb/min (3.8 g/s). I've read that high trims at idle could imply a vaccum leak, particularly if trims resolve at higher rpm.

When I hold at 2500 rpm, this is when I see what seems odd. LTFT is near 10-14% for both banks and STFT is +/- a couple of %. MAF is about 1.77 lb/min (14 g/s). Compared to my 5th gen at 2500 rpm where LTFT and STFT are +/- a few %.

Anyone have any luck diagnosing these codes further with a scan tool? I will wait for freeze frame data when they pop up again for further information. I did replace gas cap (Stant) and cleaned MAF. Nothing obvious under the hood.

Thanks!

 

[MikeinNH67]

I'd start by checking all the hoses to see if you have a cracked one giving you a vacuum leak. Bad leaks you can usually hear. Could also try spraying some flammable brake cleaner sparingly around things. If the RPMs jump then you have a leak in that area.

 

[BigMike18]

I had a similar issue in my 05 2UZ, but mine ended up funneling too much air from cracked fuel injector grommets.

Yours makes me think fuel because at higher rpms it doesn't diminish. My thoughts are towards fuel injector, fuel pump, fuel filter, or MAF, MAP, O2 sensors. If lean conditions are present both under vacuum and acceleration, it’s almost always fuel delivery or a large air leak between MAF (if equipped) and throttle plate.

 

[mooch91]

Reporting back - SOLVED.

Replaced the MAF sensor with a Denso purchased off of Amazon. The STFT and LTFT trims came down to single digit +/- numbers at all RPMs across the range. Didn't think I'd get as lucky as it being the sensor, but it worked out.

 

[The3rdGen]

Hey, Newer account and I cant make my own thread. Just wanted to put this out there, I fought uphill with my 2006 4Runner Sport, V8 having both P0171 and P0174 Codes. Previous owner severely neglected it and it was throwing 17 codes when i first got it.
It would run rough, Struggled to get up to speed and often would "surge" As if were maybe hesitating to change gears, almost felt line a Transmission issue.
Off the line, if you pressed the accelerator all the way it would stumble harshly and backfire, refusing to accelerate.

Did everything you could imagine, ran all fuel system cleaners, MAF, changed Spark plugs with OEM Plugs, Replaced Vacuum valves for the fuel system, New Air Filter, Replaced all vacuum lines, Replaced intake manifold Gaskets, Cleaned the Injectors, Changed the Fuel Pump Relay, removed and cleaned throttle body, replaced gasket you name it....
Was getting 11 to 14 MPG Hwy/City before I Finally solved it.
My big breakthrough was found when i Jumped the contacts on the Fuel Pump Resistor. Instantly it began to run better. No more hesitation off the line and fuel economy improved.
I Decided to pull the unit and replace the Pump, Level sender and the screen-filter under the pump. I Wish i had taken photos of just how nasty this small filter was. No doubt it was the underlying problem. Likely it had never been changed in almost 290,000 miles. It now runs like a new truck. Cranks and fires almost instantly, no hesitation. Runs way stronger and smoother, Gets 22mpg Hwy and 16 City. Absolute night and day difference, truly wish i had done this sooner as i had been scratching my head for over a year with this issue.

 

[PNWDave44]

Created an account just to say thank you for this information! I've also been having odd issues with running a bit lean. Read your post and went to Ohm out my Fuel Pump Resistor. It is showing 1.1ohms resistance when the FSM say's it should be between 0.70-0.76 @68F. I will jump it and see if it makes a difference. Do people just drive around with the system jumped to test it out? I.e. bridge the 2 leads on the wire harness that plugs into the Fuel Pump Resistor?

 

[asb1230]

I need help diagnosing my 4Runner (2016, 135k miles). I’m getting P0174, and more recently P0171 showed up too. These indicate lean mixtures in both engine blocks. No other codes. The data on my scanner doesn’t seem to add up (pic below). Both the downstream O2 sensors are reading about 0.7-0.8V. From what I read in the service manual, that would indicate a rich condition. But the STFT coming from both those sensors is 99%. On top of that, the lambda from the upstream sensors is about 1.0, which makes me think the actual mixture is good. Any ideas on what I should do next?

Here are the O2 sensor voltages from the service manual.

Here's the live data I captured at idle.

 

[AuSeeker]

I need help diagnosing my 4Runner (2016, 135k miles). I’m getting P0174, and more recently P0171 showed up too. These indicate lean mixtures in both engine blocks. No other codes. The data on my scanner doesn’t seem to add up (pic below). Both the downstream O2 sensors are reading about 0.7-0.8V. From what I read in the service manual, that would indicate a rich condition. But the STFT coming from both those sensors is 99%. On top of that, the lambda from the upstream sensors is about 1.0, which makes me think the actual mixture is good. Any ideas on what I should do next?

Here are the O2 sensor voltages from the service manual.

Here's the live data I captured at idle.

This is the 4th Gen forum, you need to seek help in the 5th Gen forum!