P0171 on a 2019 Ford F 350 Crew

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 2019 Ford F 350 Crew

Ranked from 463 NHTSA owner complaints filed for this vehicle.

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1
CP4 fuel pump / fuel filter / fuel line failures reducing fuel delivery pressure
High severity
An unusually large cluster of complaints describes the CP4 high-pressure pump failing and fuel filter housings/lines cracking or blowing off on this 6.7L Powerstroke, any of which starves the engine of fuel pressure and can register as a lean condition.
Reported in 11 NHTSA complaints
Parts:fuel pump fuel filter fuel line
2
Mass airflow (MAF) sensor fault
High severity
A reported known MAF problem on the 6.7L engine, tied to failed regen and limp mode, is a documented lean-condition trigger on this platform.
Reported in 1 NHTSA complaint
Parts:MAF sensor
3
Vacuum or intake leak
Medium severity
Unmetered air entering after the MAF sensor (cracked boot, loose clamp) leans out the mixture; smoke-test the intake tract.
Common cause
Parts:intake gasket
4
Intake manifold gasket failure
Medium severity
A leaking intake gasket admits unmetered air directly into the manifold, producing a persistent lean code.
Common cause
Parts:intake manifold gasket
5
Stuck-open PCV/crankcase vent valve
Low severity
A PCV valve stuck open pulls excess unmetered air into the intake, leaning the mixture especially at idle.
Common cause
Parts:PCV valve
6
Exhaust leak upstream of the air/fuel sensor
Low severity
A leaking exhaust joint ahead of the front sensor draws in outside air and can bias the sensor toward a lean reading.
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