P0171 on a 2017 Ford F 350 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 2017 Ford F 350 Regular Cab

Ranked from 560 NHTSA owner complaints filed for this vehicle.

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1
Cracked fuel filter housing or fuel line leak
High severity
Numerous owners reported the fuel filter housing cracking or a fuel line splitting, spraying diesel and (before failing completely) allowing air into the low-pressure fuel circuit, which starves/leans the injection system.
Reported in 6 NHTSA complaints
Parts:fuel filter housing fuel lines
2
CP4 high-pressure fuel pump failure (implodes and sends metal through the fuel system)
High severity
Multiple owners describe the CP4 high-pressure pump imploding/failing and contaminating or starving the fuel system, causing loss of power and stalls — a well-documented failure on 2017 6.7L Powerstroke trucks.
Reported in 4 NHTSA complaints
Parts:high-pressure fuel pump fuel filter fuel injector
3
Fuel contamination (water, DEF, or tank-lining debris)
Medium severity
One owner accidentally introduced DEF fluid into the fuel tank and another reported tank-lining material flaking into the fuel; contaminated fuel disrupts injector metering and can register as a lean/fuel-trim fault.
Reported in 2 NHTSA complaints
Parts:fuel filter fuel tank
4
Intake/charge-air leak (turbo boost leak)
Medium severity
A leaking intercooler pipe or clamp lets in unmetered air, which on turbocharged diesels can skew the mass-airflow-based fuel calculation toward lean.
Common cause
5
Dirty or failing MAF sensor
Medium severity
An MAF that under-reports intake airflow causes the PCM to under-fuel relative to actual air entering the engine.
Common cause
Parts:MAF sensor
6
Exhaust leak upstream of the exhaust gas sensor
Medium severity
Outside air drawn in ahead of the sensor is misread as excess oxygen, prompting the PCM to lean fueling further.
Common cause
7
EGR valve stuck open
Low severity
Excess EGR flow dilutes the intake charge beyond the calibrated range and can present as a lean-fuel-trim style fault.
Common cause
Parts:EGR 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