P0171 on a 2017 Ford F 250 Crew 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 2017 Ford F 250 Crew Cab

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

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1
Vacuum leak from a failed intake manifold
Medium severity
Dealer-diagnosed intake manifold failures on this truck (abnormal knocking/ticking, no warning light) let unmetered air past the MAF, leaning the mixture especially at idle.
Reported in 2 NHTSA complaints
Parts:intake manifold intake manifold gasket
2
Weak or failing low-pressure fuel (lift) pump
Medium severity
A lift pump that loses prime can't keep the rail satisfied, leaning the mixture under load; one owner's 6.2L gas engine showed exactly this pattern with a faulty check valve.
Reported in 1 NHTSA complaint
Parts:fuel pump
3
Vacuum or intake air leak (hoses/gaskets)
Medium severity
Cracked vacuum lines or a leaking throttle-body gasket admit unmetered air; smoke-testing the intake will reveal the leak point.
Common cause
Parts:vacuum hose intake gasket
4
Dirty or failing MAF sensor
Low severity
A contaminated or drifting mass airflow sensor under-reports incoming air so the PCM under-fuels the engine.
Common cause
Parts:mass airflow sensor
5
Exhaust leak upstream of the O2/A-F sensor
Medium severity
A leaking exhaust manifold gasket or cracked downpipe ahead of the sensor lets in extra oxygen that the PCM misreads as a lean condition.
Common cause
Parts:exhaust manifold gasket
6
Stuck-open PCV valve
Low severity
A PCV valve stuck open draws unmetered air into the intake, skewing fuel trims lean at idle.
Common cause
Parts:PCV valve

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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