Did the codes appear before or after the transmission flush?

I don't have much to add regarding p0756. It is possible p0756 is driven by the p0171, the latter which might be easy to clear. So I would start with p0171 if possible.
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p0171 is fuel system too lean.

Generic areas I might check include:

- vacuum leak. You can look for leak, listen for hiss, do a smoke test... Also check that your dipsticks are undamaged, fully inserted, fuel & oil caps are on properly / in good condition.
- check air intake system is clear and tight. check air filter is clean.
- MAF dirty or failing (you can clean but need to use special cleaner spray only)
- Throttle body dirty (see instructions on forum)
- fuel system cleaner
- pcv system / valve
- fuel pump
- I don't know if cleaning the EGR/passages would help this but this is popular Fit issue
- For fun, I also would quickly check voltage on battery terminals when car is running is in spec (say above 14v but look around). Low voltage can cause odd system issues and the Fit battery is so tiny you don't have a lot of cushion.

Some cheap consumer gizmos let you look at ST and LT fuel trims, MAF reading, temperatures, etc. real-time to help diagnose. I have a scangauge but I think there are some cheap bluetooth OBD systems that work with a phone. These can help you get to bottom of problem faster. And see if any of your fixes above are impacting real-time.

Here is another take:
https://www.700r4transmissionhq.com/p0171-honda-fit/

 

 

Man, fiting, must be nice being smart.
I pulled some stuff from the manual for yuh sir.





This one is for relieving fuel pressure without the fancy honda whatsit.

if your tranny issues persist.. run redline D6 atf. honestly I'd be runnin that stuff either way. I couldnt be more confident in this company's products and I've seen it fix stuff first hand, improved smoothness and function over oem.... and no, they dont pay me. Wish they did.

 

Just to confirm the first code is P0171 and not P0711.....
P0711 is an auto trans trouble code for atf temp sensor range performance problem and is discussed in the factory repair manual in sec.14-91.

If the first code is def. P0171- are you running an after-market intake? These intakes are known to trigger the P0171 code. Also double check that your mass air flow sensor (MAF) wiring to the sensor in the air cleaner/ intake is tight and the pins in the connector are straight. If the MAF sensor wiring is not connected, it will cause the auto trans to shift weird.

 

hahaha! Truth is that our family has a lot of old cars that have a lot of problems so we have run by a lot of these codes, including the p0171.

These printouts and tips are goldmines...

 

I used to work on the abrams tanks, but leadership being what it was I only got so much hands on time for repairing failures. Near all went to PMCS n operating. Came home and started automotive stuff
​​​​​​since then ive broken thousands of dollars worth of stuff a strong jealousy formed toward sharp people.

Accolades n life story aside, more good info. What I wanted to add was a little trick a friend taught me (that some of you likely know).
read in one of those procedures you needed to power some kinda clicker. Taken to using this method for testing relays n cleaning injectors instead of sendin em off, works for whatever.

Ring terminals, 14gauge wire (suitable for 5 amps at 20ft), and mini quick disconnects. I just loosen the female heads a little with a knife or whatever so that they dont grip pins or prongs too tight. Rings go to the battery, so just buy a proper size.. or do whatever if you have a portable 12v dc power supply

edit:

 

 

Good clues.

Put a normal air filter in. Then you need to clean the MAF with special MAF cleaner as the MAF is hyper sensitive to oils. This has a reasonable possibility of causing the p0171 code but won't know until you try.

Also cleaning MAF may not fix it. . .

 

Below is fantastic tutorial diagnosing a "lean" situation. Explains what is happening in clear language with pictures. It only takes 5 minutes to read and I felt a lot smarter afterwards.

https://www.vauxhallownersnetwork.co...n-warm.839453/

EDIT - my cheap home DIY reader does not output these pretty scope readings, but outputs the data realtime so diagnosis is the same. . .