P0171 on a 2016 Ford Explorer

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 2016 Ford Explorer

Ranked from 2,432 NHTSA owner complaints filed for this vehicle.

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1
PCV/crankcase ventilation system failure
High severity
An owner's crankcase sensor failed and allowed crankcase pressure to build, bursting the turbo intake hose - a PCV-system fault that also lets unmetered air/pressure disrupt the intake, a documented P0171 contributor.
Reported in 1 NHTSA complaint
Parts:PCV valve
2
Charge-air/turbo intake hose leak
Medium severity
The same failure burst the turbo intake hose, creating a post-MAF vacuum/boost leak that would bias fuel trims lean.
Reported in 1 NHTSA complaint
3
Turbocharger oil seal leak fouling the MAF sensor
Medium severity
An owner had a turbo replaced for an oil leak; oil migrating into the intake can coat and desensitize the MAF sensor, causing it to under-report airflow.
Reported in 1 NHTSA complaint
Parts:MAF sensor turbocharger
4
Intake manifold gasket leak
Medium severity
A leaking manifold gasket admits unmetered air downstream of the MAF sensor, producing a lean condition.
Common cause
5
Vacuum leak (hoses/connectors)
Medium severity
Cracked or disconnected vacuum lines are a common, easy-to-find source of a lean condition.
Common cause
6
Weak fuel pump or low fuel pressure
Medium severity
Insufficient fuel delivery can't match commanded fueling under higher airflow demand, registering lean.
Common cause
Parts:fuel pump
7
Exhaust leak upstream of the front oxygen sensor
Low severity
Outside air drawn in ahead of the sensor skews readings toward lean.
Common cause

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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