P0171 on a 2020 Ford F 150 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 2020 Ford F 150 Supercab

Ranked from 506 NHTSA owner complaints filed for this vehicle.

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1
Low fuel rail pressure / weak fuel pump
High severity
One owner's check-engine light came with code P0087 (low fuel rail pressure), a direct cause of a lean-running condition on this truck.
Reported in 1 NHTSA complaint
Parts:fuel pump fuel pressure sensor
2
Exhaust leak upstream of the front oxygen sensor
Medium severity
This truck has a documented factory turbo-mounting/bolt design flaw that lets the exhaust manifold warp and leak, which draws outside air in ahead of the sensor and reads as lean.
Reported in 1 NHTSA complaint
Parts:exhaust manifold gasket
3
Dirty or failing mass airflow (MAF) sensor
Medium severity
A contaminated or drifting MAF under-reports incoming air; one owner also noted a marked drop in fuel economy consistent with an airflow-metering error.
Reported in 1 NHTSA complaint
Parts:mass airflow sensor
4
Vacuum or intake air leak
Medium severity
Unmetered air entering after the MAF causes the ECM to under-fuel; inspect intake boots, PCV, and vacuum hoses.
Common cause
5
Clogged fuel filter
Medium severity
A restricted filter starves the engine of fuel under load, producing the same lean signature as a weak pump.
Common cause
Parts:fuel filter
6
Stuck-open PCV valve
Low severity
A PCV valve stuck open pulls extra unmetered air into the intake at idle.
Common cause
Parts:PCV valve
7
Intake manifold gasket leak
Medium severity
A leaking gasket admits unmetered air directly into the manifold, producing a lean bank code.
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