P0171 on a 2018 Ford F 250 Regular 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 Regular Cab

Ranked from 382 NHTSA owner complaints filed for this vehicle.

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1
Weak/failing fuel pump or fuel pressure control valve
High severity
This F-250 generation is heavily reported for HPFP/LPFP and fuel-pressure-control-valve failures that drop rail pressure below spec, which the PCM reads as a lean condition before the pump fails outright.
Reported in 9 NHTSA complaints
Parts:fuel pump fuel pressure control valve fuel filter
2
Stuck EVAP purge or fuel-pump check valve bleeding down fuel pressure
Medium severity
One owner's detailed write-up traces sputtering and extended crank time to a stuck EVAP purge/check valve that lets fuel-line pressure bleed off overnight, which can register as a lean trim on startup.
Reported in 1 NHTSA complaint
Parts:EVAP purge valve fuel pump check valve
3
Vacuum or intake air leak
Medium severity
Unmetered air entering downstream of the MAF sensor causes the PCM to under-fuel and trim lean.
Common cause
4
Dirty or failing MAF sensor
Medium severity
A contaminated or drifting MAF under-reports intake airflow, causing the PCM to add too little fuel.
Common cause
Parts:mass air flow sensor
5
Stuck-open PCV valve
Low severity
A PCV valve stuck open pulls excess unmetered air into the intake.
Common cause
Parts:PCV valve
6
Exhaust leak upstream of the oxygen sensor
Medium severity
Outside air drawn in through an exhaust leak skews the O2/air-fuel sensor reading lean.
Common cause
7
Intake manifold gasket failure
Medium severity
A leaking manifold gasket admits unmetered air directly into the cylinders.
Common cause
Parts:intake manifold gasket

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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