P0171 on a 2019 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 2019 Ford Explorer

Ranked from 285 NHTSA owner complaints filed for this vehicle.

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1
Faulty Fuel Pump / Fuel Pump Module
High severity
Low fuel pressure prevents enough fuel from reaching the engine, causing a lean condition. Confirmed by testing fuel pressure and inspecting the fuel pump module.
Reported in 2 NHTSA complaints
2
Vacuum Leak (Intake Manifold / Hoses)
Medium severity
Unmetered air entering the engine leans out the air/fuel mixture. Look for disconnected, cracked, or loose intake hoses or a disconnected air intake manifold.
Reported in 1 NHTSA complaint
3
Faulty Fuel Injectors
Medium severity
Clogged or failing fuel injectors restrict fuel delivery to the cylinders, leading to a lean mixture. Confirmed by injector flow testing or misfire/lean codes.
Reported in 1 NHTSA complaint
4
Faulty Manifold Absolute Pressure (MAP) Sensor
Low severity
An inaccurate MAP sensor can cause incorrect fuel delivery calculations. Confirmed by checking sensor voltage/pressure readings against actual manifold vacuum.
Reported in 1 NHTSA complaint
5
Exhaust Leak Before the O2 Sensor
Medium severity
An exhaust leak introduces outside oxygen into the exhaust stream, tricking the O2 sensor into reading lean. Look for cracked exhaust manifolds or improper welds.
Reported in 1 NHTSA complaint
6
Faulty Mass Air Flow (MAF) Sensor
Low severity
A dirty or failing MAF sensor incorrectly measures incoming air, causing the PCM to under-fuel the engine. Confirmed by checking MAF sensor data via scan tool.
Common cause
7
Faulty Oxygen (O2) Sensor
Low severity
A degraded upstream O2 sensor may falsely report a lean condition. Confirmed by monitoring O2 sensor voltage switching and response time.
Common cause
8
PCV Valve / System Leak
Low severity
A stuck open PCV valve or leaking PCV hose acts as a vacuum leak, introducing unmetered air. Confirmed by inspecting PCV hoses and valve operation.
Common cause

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