P0171 on a 2017 Ford F 350 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 350 Supercab
Ranked from 560 NHTSA owner complaints filed for this vehicle.
- 1
High-pressure (CP4) fuel pump failure causing low fuel rail pressure / fuel starvation
High severityThis platform has an extremely well-documented CP4 high-pressure pump failure mode (implosion, metal contamination, sudden power loss/shutdown) reported repeatedly in this batch, which starves the engine of properly pressurized fuel and can register as a lean condition.
Reported in 8 NHTSA complaints - 2
Fuel filter housing crack or fuel-line leak allowing air intrusion into the fuel supply
High severityRepeated fuel filter housing cracks and a broken fuel line at the filter top let air enter the low-pressure fuel circuit, reducing delivered fuel volume/pressure.
Reported in 5 NHTSA complaints - 3
Contaminated or diluted fuel (DEF fluid or fuel tank liner debris)
Medium severityFuel contamination events (DEF accidentally added to the tank; flaking fuel-tank liner) degrade combustion quality and delivered fuel energy, consistent with a lean-running condition.
Reported in 2 NHTSA complaints - 4
Charge air cooler/intake boost leak from restricted CCV separator (2017-2019 6.7L design issue)
High severityA restricted crankcase oil separator on this exact engine/model-year range is documented to cause secondary charge-air-cooler tube splits, letting unmetered air enter the intake and skew the air/fuel ratio lean.
Reported in 1 NHTSA complaintParts:charge air cooler tube - 5
Failing or dirty mass airflow (MAF) sensor
Medium severityA drifted MAF sensor under-reports intake air, causing the PCM to under-fuel and register a lean trim.
Common causeParts:MAF sensor - 6
Intake or turbo boost leak (cracked hose/loose clamp)
Medium severityA boost/intake leak downstream of the MAF lets unmetered air into the engine, producing a lean trim under load.
Common causeParts:intake hose - 7
Weak lift (low-pressure) pump or clogged fuel filter
Medium severityInsufficient low-pressure fuel supply to the high-pressure pump reduces overall fuel delivery, a standard lean-condition contributor.
Common causeParts:fuel filter
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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.