P0171 could be caused by a number of things, and it sounds like your mechanic checked most of the stuff.

Do you know if he checked the MAF? (Mass Airflow Sensor).

 

P0171 could be caused by a number of things, and it sounds like your mechanic checked most of the stuff.

Do you know if he checked the MAF? (Mass Airflow Sensor).

I believe so and I believe he said he cleaned it. Would a dirty sensor cause a rough idle? Could it be a spark plug issue?

 

If the engine shake, i would lean to diagnose as fuel injector issue even though spark plug crack porcelain crack may also possible. To disconnect the wiring for fuel injector if possible then may give quick result

 

The MAF sensor monitors the air going into the engine.That air is fed to both banks evenly.Therefore,if it was the MAF then both banks should be running lean and not just one.My bet is on a bad injector.I suggest that you check the connection at each one.If the connections are good then exchange the injectors from one bank to the other,clear the codes and drive it.If an injector is bad then the code will change indicating that the other bank is now lean.

 

Interesting. Thanks for that info. I’ve never personally check injectors before, so I’ll have to check out a youtube on how to.

 

While the MAF does feed both banks evenly, a dirty, or faulty MAF WILL throw that code. However, it could very well be a injector issue.

The Problem with this code, is it's really kind of all over the place, O2 sensor, leak in a hose, MAF, fuel injector, etc.

 

Well folks, turns out I have an oil leak, fuel injector isn’t sitting correctly, and will probably need to replace the O2 sensor and the MAF sensor. They say they need to lift the engine to seal everything, which I think is maybe BS, but I don’t know. Fortunately, this is all covered under warranty, so I only have $100 deductible.
Really hoping this doesn’t happen again for a long time, but this has put a bad taste in my mouth about my year of Crosstreks. Bummed.

 

I can see it being one, or the other, and maybe even two of those, but oil leak, fuel injector, O2 Sensor and MAF seems like they are fixing everything as opposed to tracking it down. For $100 though....might as well.

 

Totally. Thanks for everyone’s help!

 

Hey Mates, I’m having an issue solving the P0171 Lean Bank code. I’m in a 2015 Subaru Crosstrek A/T. 51,000 miles. Typically use 89 gasoline. Solid check engine light and traction control light are on. Engine trembles or shakes a bit (rough) when idle. Traction light turns off sometimes, and check engine will even turn off sometimes. But always comes back when I fill the tank. I took it to my mechanic. He’s a Honda specialist but I still go to him since he’s been my mechanic for 20 years. He checked everything, no hose or intake leaks, no cracks, he couldn’t find the issue. He even cleaned the ox sensor. He said if the light stays on, I should take to Subaru or Subaru specialist, but before I do that, I wanted to ask you all if you have any ideas. Has anyone experienced this same situation? Anything I should do or check before I go to Subaru? Thanks!! -AA

I know its been a while but figured I would include my experience. I have a 2013 Crosstrek and have had a rough idle for a few months now, especially at startup. No engine codes/lights. I was recently on a 3500 mile road trip and experienced a check engine light and traction control light. lost cruise control, so I stopped at a parts store before shutting down the engine. I plugged in my code reader and found the P0171 code for lean bank. I removed the air filter and bought a 5 dollar can of MAF sensor cleaner. I removed the MAF sensor and found it to have a very light thin layer of dust on the sensor. I sprayed it clean and re-installed. I bought a new air filter and replaced the old one. I cleared the codes and started the engine. It starts and idles perfect now. No more rough idle. Also have noticed more direct acceleration from a stop. I have completed the road trip, about 2500 miles since the repair, still running great. I have just replaced my plugs as I believe the car still had the original plugs. The car is now at 183,000+ miles. I don't know when the last time the timing set was changed so that is the next project.

 

Your ecu sets the ignition timing. You might clean the throttle body next.