Will bad gas cause a P0171 code pop up

Hello, no, I would say bad gas will not cause a "lean" fuel trim code to set. Lean codes come on due to too much air getting into the engine relative to fuel delivery. This can happen due to unmetered air leaks from the intake manifold, vacuum leaks or less often a sensor concern such as with the mass air flow sensor. Testing and hands on inspection of the vehicle to ensure all connections are intact and not allowing air into the engine unexpectedly is needed. https://repairpal.com/auto-repair-near-me Click the link or call us at 877-913-1554. We'll gladly find you a certified RepairPal shop in your area.