P0171 on a 2019 Ford F 350 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 2019 Ford F 350 Regular Cab

Ranked from 463 NHTSA owner complaints filed for this vehicle.

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1
Fuel filter/fuel line failure (cracking housing, failed clips) causing fuel starvation or air ingestion
High severity
Multiple owners report the upper fuel filter housing/connecting lines on the 6.7L Powerstroke cracking or blowing off, spraying diesel and starving the fuel rail of pressure; air/fuel restriction downstream reads as a lean condition.
Reported in 5 NHTSA complaints
Parts:fuel filter fuel line
2
CP4 high-pressure fuel pump failure sending metal debris through the fuel system
High severity
Several complaints describe the CP4 pump failing and shedding metal shavings into injectors/fuel rail, reducing fuel delivery pressure and consistency (same pump family later recalled on 2020-2022 trucks).
Reported in 5 NHTSA complaints
Parts:high-pressure fuel pump fuel injectors fuel rail
3
Dirty or failing mass airflow (MAF) sensor
Medium severity
Owner cites a Ford technical service bulletin for known MAF problems on 6.7L engines causing limp mode; an inaccurate MAF signal is a classic driver of a false lean-fuel-trim code.
Reported in 1 NHTSA complaint
Parts:mass airflow sensor
4
Vacuum or charge-air/intake leak
Medium severity
Unmetered air entering after the MAF (cracked boot, loose clamp, leaking intake gasket) causes the PCM to under-fuel, triggering a lean code.
Common cause
5
Exhaust leak upstream of the front oxygen/air-fuel sensor
Low severity
A leak ahead of the sensor draws in outside air, making the engine appear leaner than it actually is.
Common cause
6
Stuck-open PCV valve
Low severity
An open PCV path admits excess crankcase air into the intake, skewing the air/fuel ratio lean.
Common cause
Parts:PCV valve
7
Intake manifold gasket leak
Medium severity
A leaking manifold gasket lets unmetered air past the MAF, a common contributor to lean-trim codes.
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