P0171 on a 2018 Ford F 250 Crew Cab

P0171 means the engine computer is adding more fuel than normal on bank 1 because it sees too much air or not enough fuel.

Not your vehicle? See general P0171 info.

Most common causes on the 2018 Ford F 250 Crew Cab

Ranked from 382 NHTSA owner complaints filed for this vehicle.

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1
Fuel delivery system failure (weak pump, clogged filter, or high-pressure pump failure)
High severity
A recurring pattern across many owners: low fuel-pressure alerts, cracked/clogged fuel filters, and low-/high-pressure pump failures (including CP4-style pump metal contamination), all consistent with a fuel-starvation-driven lean condition.
Reported in 8 NHTSA complaints
Parts:fuel pump fuel filter
2
EVAP purge/vent valve fault disrupting fuel-tank pressure
Medium severity
Owner traces extended-crank/sputter symptoms to a stuck EVAP purge valve and dust-contaminated vent path bleeding off fuel-line pressure.
Reported in 1 NHTSA complaint
Parts:purge valve
3
Vacuum or intake air leak
Medium severity
Unmetered air entering after the MAF causes the ECM to read lean.
Common cause
4
Dirty or failing MAF sensor
Medium severity
An underreporting MAF causes the ECM to under-fuel.
Common cause
Parts:mass airflow sensor
5
Exhaust leak upstream of the O2 sensor
Low severity
Extra air reaching the sensor ahead of the catalyst makes the system read falsely lean.
Common cause
6
Intake manifold gasket failure
Medium severity
A leaking manifold gasket is a common unmetered-air path.
Common cause
Parts:intake manifold gasket
7
Stuck-open PCV valve
Low severity
An open PCV path adds unmetered air to the intake.
Common cause
Parts:PCV valve

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These causes are aggregated from NHTSA owner complaints and general repair knowledge — this is not a diagnosis. P0171 on your car still needs shop confirmation before any repair.

Common symptoms

Check engine light
Rough idle
Hesitation
Surging idle
Poor fuel economy

What to check before replacing parts

Review short- and long-term fuel trims on bank 1

Look for: High positive trims (commonly worse at idle, improving with RPM) mean the computer is adding fuel to compensate for excess air or insufficient fuel — that pattern is this code's fingerprint.

Smoke-test the intake

Look for: Smoke escaping (or a hiss you can hear) at intake boots, gaskets, or vacuum hose connections confirms unmetered air is entering after the MAF sensor, which is the most common cause of a lean code.

Inspect the PCV hoses and valve

Look for: A cracked, split, or disconnected PCV hose, or a PCV valve stuck open, draws in extra unmetered air the same way a vacuum leak does.

Clean and test the MAF sensor

Look for: Visible dirt or oil film on the sensor element, or a grams/second reading that doesn't track expected airflow for RPM, means the MAF is under-reporting air and causing the computer to under-fuel.

Verify fuel pressure

Look for: Pressure below spec (weak pump, clogged filter, failing regulator) starves the engine of fuel and produces the same lean trim pattern as a vacuum leak — rule it out before chasing leaks.

Rather have a pro handle it? Find a vetted local mechanic.

Matching symptoms

Car Runs Rough