P0171 Ford F-150
System Too Lean (Bank 1) · Powertrain Code · High · Repair: Moderate
What is P0171?
The engine is running lean on bank 1 — too much air or not enough fuel. Common causes include vacuum leaks, weak fuel pump, clogged fuel injectors, or a faulty MAF sensor.
When the Ford F-150 triggers code P0171 (system too lean (bank 1)), it typically points to an issue in the powertrain system. This is a high severity code, so address it promptly to avoid further damage or safety concerns. Below you'll find the most common causes, symptoms, and repair options specific to the Ford F-150.
This repair is rated moderate, meaning some experience and specialty tools required.
Diagnostic data on this page is compiled from publicly available repair resources and technical service bulletins. Always have a qualified mechanic confirm the diagnosis before authorizing repairs on your Ford F-150.
Common Causes on Ford F-150
- PCV system hose failure or elbow crack on 3.5L or 2.7L EcoBoost causing vacuum leak
- Charge air cooler (intercooler) condensation causing lean stumble on EcoBoost in humid climates
- MAF sensor contamination from aftermarket oiled air filter on 5.0L Coyote or EcoBoost
- Intake manifold runner control actuator failure on 5.0L Coyote V8
- Exhaust leak at manifold causing false lean reading on wideband O2 sensors
Symptoms
- Rough or unstable idle speed
- Hesitation or stumble during acceleration
- Engine surging or hunting at idle
- Lean misfire under load causing jerking
- Poor acceleration response and reduced power
- Check engine light illuminated
Notes for Ford F-150
EcoBoost charge air cooler condensation can cause a momentary lean condition in humid weather.