P0171 on a 2019 Ford F 350 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 2019 Ford F 350 Supercab

Ranked from 463 NHTSA owner complaints filed for this vehicle.

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1
Cracked upper fuel filter housing or fuel line causing air ingestion / fuel pressure loss
High severity
A repeatedly-reported cracked fuel filter housing/connecting line on top of the 6.7L lets air into the low-pressure fuel circuit and sprays diesel instead of delivering it, both of which can pull fuel trims lean.
Reported in 6 NHTSA complaints
Parts:fuel filter housing fuel line
2
CP4 high-pressure fuel pump failure causing low/erratic fuel rail pressure
High severity
Multiple owners describe the same CP4 pump used on this pre-2020 truck internally disintegrating and contaminating the fuel system, which starves the rail and can register as a lean condition before the engine loses power entirely.
Reported in 4 NHTSA complaints
Parts:high-pressure fuel pump fuel injectors fuel filter
3
Mass airflow (MAF) sensor fault (known 6.7L service bulletin)
Medium severity
A documented MAF issue on these engines skews the ECM's fuel calculation, producing a lean trim and limp-mode symptoms as described in the complaint referencing the MAF bulletin.
Reported in 1 NHTSA complaint
Parts:mass airflow sensor
4
Fuel tank or filler-neck leak reducing effective fuel delivery
High severity
A leak from the top of the fuel tank while parked reduces fuel volume/pressure reaching the engine and can contribute to a lean trim reading in addition to being a fire hazard.
Reported in 1 NHTSA complaint
Parts:fuel tank
5
Turbocharger failure or boost/intake air leak
High severity
A reported turbo and engine failure with clanking noise is consistent with unmetered air entering downstream of the MAF, which the ECM reads as a lean condition.
Reported in 1 NHTSA complaint
Parts:turbocharger
6
Vacuum or intake air leak
Medium severity
Any crack in intake boots, PCV lines, or gaskets lets in unmetered air, a standard cause of a lean fuel-trim code.
Common cause
7
Clogged or restricted low-pressure fuel filter
Medium severity
A plugged filter starves the high-pressure pump of adequate fuel volume, a classic lean-condition cause independent of the pump itself.
Common cause
Parts:fuel filter
8
Exhaust leak upstream of the oxygen/wide-band sensor
Medium severity
An exhaust leak draws in outside air ahead of the sensor, causing the ECM to falsely read the mixture as lean.
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