P0171 on a 2017 Ford F 250 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 2017 Ford F 250 Supercab

Ranked from 1,155 NHTSA owner complaints filed for this vehicle.

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1
Failing high-pressure fuel pump / fuel delivery system (CP4 pump, cracked fuel filter housing & lines)
High severity
Numerous complaints on this vehicle describe the CP4 high-pressure pump cracking and shedding metal debris, or the fuel filter housing/lines cracking and leaking, all reducing delivered fuel volume/pressure — a well-documented pattern on 2017 6.7L Powerstroke trucks that can present as a lean condition.
Reported in 10 NHTSA complaints
Parts:high-pressure fuel pump fuel filter fuel lines
2
Defective/cracked intake manifold causing vacuum leak
Medium severity
Two separate complaints on this vehicle had the intake manifold diagnosed as defective after an abnormal knocking/ticking sound, which admits unmetered air and leans the mixture.
Reported in 2 NHTSA complaints
Parts:intake manifold intake manifold gasket
3
Vacuum or intake air leak
Medium severity
Unmetered air drawn in past the mass air flow sensor leans the mixture; check intake boots, PCV hoses, and the brake booster line for cracks or loose clamps.
Common cause
4
Dirty or failing mass air flow (MAF) sensor
Medium severity
A contaminated or drifting MAF under-reports incoming air, so the PCM commands less fuel than the engine actually needs; cleaning or replacement confirms it.
Common cause
Parts:mass air flow sensor
5
Weak fuel pump or clogged fuel filter
Medium severity
Insufficient fuel delivery/pressure produces a lean condition, especially under load or acceleration; check measured fuel rail pressure against spec.
Common cause
Parts:fuel pump fuel filter
6
Stuck-open PCV valve
Low severity
Excess crankcase air enters the intake unmetered and leans the mixture; inspect and replace the PCV valve and hose.
Common cause
Parts:PCV valve
7
Exhaust leak upstream of the front O2/air-fuel sensor
Low severity
Outside air drawn in near the sensor before the engine reaches full temperature skews the reading lean.
Common cause
8
Intake manifold gasket failure
Medium severity
A leaking manifold gasket admits unmetered air directly into the runners; common on higher-mileage engines and often accompanied by a rough or erratic idle.
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