P0171 on a 2020 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 2020 Ford F 150 Supercab Diesel

Ranked from 506 NHTSA owner complaints filed for this vehicle.

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1
Exhaust leak upstream of the O2/air-fuel sensor
Medium severity
One owner describes a factory turbo-mounting flaw that warps the exhaust manifold and breaks mounting bolts, opening an exhaust leak ahead of the sensor -- exactly the kind of leak that skews the sensor lean.
Reported in 1 NHTSA complaint
2
Weak fuel pump / low fuel rail pressure
Medium severity
One owner's scan showed a low fuel-rail-pressure code (P0087) alongside slow starts and power loss at high demand -- consistent with a fuel-delivery shortfall that also drives the mixture lean.
Reported in 1 NHTSA complaint
Parts:fuel pump
3
Vacuum or intake leak
Medium severity
Unmetered air past the MAF sensor is the single most common cause of a lean bank code; check intake boots, PCV hoses, and brake booster line.
Common cause
4
Dirty or failing MAF sensor
Medium severity
A contaminated or drifting MAF under-reports incoming air, causing the PCM to under-fuel and trip a lean code.
Common cause
Parts:MAF sensor
5
Stuck-open PCV valve
Low severity
A PCV valve stuck open adds unmetered air to the intake, leaning the mixture especially at idle.
Common cause
Parts:PCV valve
6
Intake manifold gasket leak
Medium severity
A leaking manifold gasket admits unmetered air directly into the runners, producing a persistent lean code.
Common cause
Parts:intake manifold gasket
7
Clogged fuel filter
Low severity
Restricted fuel flow from a clogged filter reduces rail pressure similarly to a weak pump, leaning the mixture under load.
Common cause
Parts:fuel filter

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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