P0171 on a 2019 Ford F 150 Supercab Diesel

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 150 Supercab Diesel

Ranked from 953 NHTSA owner complaints filed for this vehicle.

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1
Weak fuel pump / low fuel pressure
Medium severity
An owner had a documented low-fuel-pressure warning and hard-starting matching a known fuel-pump defect pattern on this model, which leans out the mixture under load.
Reported in 1 NHTSA complaint
Parts:fuel pump
2
Exhaust leak upstream of the O2 sensor
Medium severity
An owner's exhaust manifold was found faulty and needing replacement; a leak there lets outside air skew the sensor reading lean.
Reported in 1 NHTSA complaint
Parts:exhaust manifold exhaust gasket
3
Vacuum or intake air leak
Medium severity
Unmetered air entering after the MAF is the most common cause of a bank-1 lean code.
Common cause
4
Dirty or failing MAF sensor
Medium severity
An under-reporting MAF causes the ECU to add too little fuel for the actual air entering the engine.
Common cause
5
Stuck-open PCV valve
Low severity
Excess uncontrolled crankcase air drawn into the intake leans out the mixture, particularly at idle.
Common cause
6
Intake manifold gasket leak
Medium severity
A worn gasket lets in unmetered air downstream of the MAF, producing a steady lean bias.
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.

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Matching symptoms

Car Runs Rough