2002 Toyota Tacoma get p0171 system too lean bank 1

Hi everyone!
After clean Maf and ran 1200 miles the code come back
Here is the freezing frame now!
Anyone can help with me to fix this code. I really appreciate your help! And it happened when I am driving on freeway and This is second time on freeway that the code show!
Thank you very much!
Thomas

 

https://repairpal.com/obd-ii-code-p0171

 

This code is usually MAF related, but could also be a vacuum leak, fuel delivery or O2 sensor as well. You really need a scanner with live data to get this sorted out, I got one for ~$100 on eBay. Here is the diagnostic procedure that helped me solve mine; I was a vacuum leak and the tech tip at the bottom confirmed it.

Tests/Procedures:
1. Monitor the fuel trim readings at idle and at 55 MPH driving down the road. If the numbers are low at idle but climb on a part throttle cruise, the airflow meter could be reading low or it may also have low fuel pressure. The mass air flow sensor grams per second should be 3.3-4.7 at idle and 12.9-18.3 at 2500 RPMs no load, if the readings are low the sensor could be bad.

2. Monitor the calculated load reading on a wide-open throttle acceleration. The reading should go to 85% or more. If not, then the airflow meter could be faulty.

3. Monitor the oxygen sensor inputs, both front and rear oxygen sensor signals. The oxygen sensor should not stay high or low voltage for extended periods of time. If the oxygen sensor shows low voltage and the fuel trim readings climb, check the performance of the oxygen sensor.

4. Check the vehicle for a vacuum leak by spraying carburetor spray around the intake manifold while watching the fuel trim readings. If the readings change, there is a vacuum leak.

Tech Tips:
If fuel trim readings are high at idle and go down on a free rev, there is a vacuum leak. If the fuel trim readings are high at idle and at cruise, suspect fuel injectors.

 

Thanks Tacotu3!
Your information is very helpful I think my fuel trim is high on freeways! If you look at images. It could be dirty injector for sure? Like you said
It happened 2 time check light on when I driving on freeway!
Thanks again!

 

Tacotu
My scanner has no live data! Only freezing data. It would help more with live data?
Thanks again!

 

YMMV but it helped me a lot, you can make some inferences with the freeze frame but you won’t be able to start eliminating causes through that diagnostic procedure without live, since you need to see how things change under different inputs.

I wanted to rule out MAF and O2 first, since those were the easiest and most definitive. Keep in mind that if it points to “injectors” that really means more “fuel delivery” in general, could be a fuel pump on the way out or clogged fuel filter too.

 

Tacotu!
Car performs well! Or hesitate even idle It normal to me. I don’t think fuel pump and fuel filter I changed every 40k! MAF I clean it when first check engine light on about 1200 miles ago and It comes back now!
Thanks for your info again! But lucky It passed smog test October 2023

 

Good luck bud, I hope you get it sorted out! Sounds like it’s not super urgent but having it dump fuel is not something you want for the long term health of the motor, and could end up damaging your cat.

 

You are right!
I smell gas too and bad for Catalytic converter!
Now! I try Techron in fuel tank if it help! Or Dealer perform injectors cleaner
Thanks again!

 

When I had a P0171 a couple years ago I found that the rubber hose leading to the IAC valve was leaking. It had no clamp on it so I installed a clamp and the problem went away.

I found it by purchasing a can of quick-start and spraying around all of the vacuum tubes while the engine was idling. Not a lot, just a little squirt. When I reached the IAC valve the engine idle sped up significantly.

 

Skeezix!
Thanks for your infor! I would do that and the easy way to do at home!
Thanks again S!
Thomas