P0171 on a 2020 Ford F 150 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 2020 Ford F 150 Regular Cab

Ranked from 506 NHTSA owner complaints filed for this vehicle.

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1
Exhaust manifold leak (factory turbo-mount bolt failure)
Medium severity
One owner documents a factory-known exhaust manifold leak from mounting bolts that break loose from heat cycling; a leak this far upstream draws outside air past the front O2/AFR sensor and reads lean.
Reported in 1 NHTSA complaint
Parts:exhaust manifold gasket exhaust manifold bolt
2
Weak fuel pump / low fuel rail pressure
Medium severity
One owner's scan showed code P0087 (fuel rail/system pressure too low) alongside hesitation and power loss at high demand, a direct lean-causing fuel-delivery shortfall.
Reported in 1 NHTSA complaint
Parts:fuel pump
3
Vacuum or intake air leak
Medium severity
A cracked hose or loose intake boot lets unmetered air past the MAF, a standard cause of a bank-1 lean code.
Common cause
4
Dirty or failing MAF sensor
Medium severity
A contaminated or drifting MAF under-reports airflow, causing the PCM to under-fuel relative to actual intake air.
Common cause
Parts:mass airflow sensor
5
Clogged fuel filter
Low severity
Restricted fuel flow reduces rail pressure under load and leans the mixture even with correct injector commands.
Common cause
Parts:fuel filter
6
Stuck-open PCV valve
Low severity
Excess unmetered crankcase air pulled through a stuck PCV valve leans the intake charge, especially at idle.
Common cause
Parts:PCV valve
7
Intake manifold gasket leak
Low severity
A failed gasket lets unmetered air past the throttle body, a common lean-code cause on higher-mileage engines.
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