P0171 on a 2018 Ford F 250 Supercab

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 Supercab

Ranked from 397 NHTSA owner complaints filed for this vehicle.

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1
Weak/failing fuel pump or fuel pressure control valve (low fuel pressure)
High severity
A large cluster of owners report the low- or high-pressure fuel pump, fuel pressure control valve, or fuel filter failing and dropping fuel rail pressure below spec; low fuel delivery relative to airflow reads as a lean condition.
Reported in 9 NHTSA complaints
Parts:fuel pump fuel filter fuel pressure regulator
2
Stuck-open EVAP purge valve pulling unmetered air into the intake
Medium severity
One owner's detailed complaint describes a faulty EVAP purge valve sticking/allowing dust ingress, pulling unmetered air past the intake and producing lean-running and hard-restart symptoms.
Reported in 1 NHTSA complaint
Parts:EVAP purge valve
3
Vacuum or intake leaks
Medium severity
A cracked charge-air hose, intake boot, or vacuum line lets in unmetered air, richening the commanded fuel trim beyond what the PCM can correct.
Common cause
4
Dirty or failing MAF/MAP sensor
Low severity
A contaminated or drifting airflow sensor under-reports intake air, causing the PCM to under-fuel and set a lean trim code.
Common cause
Parts:mass airflow sensor
5
Stuck-open PCV valve
Low severity
A PCV valve stuck open draws excess crankcase air into the intake, leaning the mixture especially at idle.
Common cause
Parts:PCV valve
6
Exhaust leak upstream of the oxygen sensor
Medium severity
A leak ahead of the O2 sensor draws in outside air, skewing the sensor reading toward lean and biasing the trim calculation.
Common cause

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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