P0171 what could be causing this?

P0171 is a Lean on bank 1 code. There are many possible causes. A vacuum leak, cracked intake gasket, injector problem, low fuel pressure, even an exhaust leak. Takes some testing to figure out where the issue is. First thing would be to look at the actual fuel trims and the O2 sensor voltages and see if the code is from something like a bad sensor of from a leak. However there isn't a simple fix. You can look at this and see if the testing helps to locate the problem -
https://2carpros.com/articles/repair-lean-mixture-codes-p0171-or-p0174-on-some-manufacturers/