P0171 on a 2015 Ford F 250 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 2015 Ford F 250 Regular Cab

Ranked from 296 NHTSA owner complaints filed for this vehicle.

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1
CP4 high-pressure fuel pump failure or fuel-system leak reducing fuel delivery
High severity
This population is dominated by the well-documented Bosch CP4 pump failure and related fuel leaks (cracked fuel-filter housing, a leaking fitting on the tank, a pump that came apart and contaminated the system) - any of which starves the injectors and drives a lean-running condition.
Reported in 7 NHTSA complaints
Parts:high-pressure fuel pump fuel filter fuel line
2
Faulty NOx/exhaust sensor giving a false lean-side reading
Medium severity
Owners report repeated NOx sensor failures and replacements on this truck's aftertreatment system; a degraded sensor can feed the ECU a reading consistent with a lean condition.
Reported in 3 NHTSA complaints
Parts:NOx sensor
3
Intake or charge-air (boost) leak
Medium severity
A split intercooler hose or boot lets in unmetered air, a leading lean-condition cause on a turbocharged diesel.
Common cause
Parts:charge air hose
4
EGR valve stuck open
Low severity
Excess EGR flow at cruise dilutes the intake charge in a way that can register as a lean condition.
Common cause
Parts:EGR valve
5
Dirty or failing mass airflow (MAF) sensor
Low severity
A contaminated MAF sensor under-reports intake air, causing the ECU to under-fuel.
Common cause
Parts:MAF sensor
6
Exhaust leak upstream of the sensor
Medium severity
A leaking exhaust manifold or downpipe joint draws in outside air that skews the reading lean.
Common cause
Parts:exhaust 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