I’m now getting 2 different fault codes on my 2017 Cooper hardtop which is just out of warranty. 46,000 miles:

P0171 System too lean Bank 1.
P0456 (EVAC system leak detected (very small leak)

I have determined that it is not the gas cap. It seems that I have no choice but to bring it in for service.
any suggestions?

Thanks

 

Look up Charcoal Canister or Vapor Canister.
Although I have a '04 R53. I have been getting a fault code 0456 (Tank~Venting system very minor leak detected). The SES light comes on every 4 cycles after clearing the code.
I replaced the seal on the original gas cap, replaced with a new gas cap, changed purge valve canister & various small "recirculation" fuel hoses under the hood - to no avail.
Finally determined it is most likely the charcoal canister under the right rear wheel well (on an R53), that needs replacing / is triggering the fault.
From what I have seen;The part is not cheap for later models ($300 -$450).
Check around $$ - I may be wrong.

 

P0456
Could be the purge valve, very common here. Main symptom is also hard start after fill ups.

 

Yes ! The 'hard start after fill up' has happened twice. I should have mentioned that in my original post. May I ask where that valve located on the F56 3-cyl?

 

Up in the front also

https://www.northamericanmotoring.co...0507-code.html


There is a bosch option now: https://www.ecstuning.com/Search/Sit...h/13907621174/

 

I hope you followed @ECSTuning link before bringing it in for service.
Your initial post had me thinking. So I checked....
In my case ( '04 R53), I discovered, I inadvertently replaced/plugged in my Fuel vent/Purge valve canister upside-down. Fixed = No more SES or P0456 tank leak fault.
The Fuel vent "valve" is in a different location (not vertical orientation) on your late model Mini. Although, I suspect that it is worth replacing at such an inexpensive cost. Check the hoses.too. It might solve your issue (?).