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P0171

P0171 on a 2021 Ford Escape Hev

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 2021 Ford Escape Hev

Ranked from 326 NHTSA owner complaints filed for this vehicle.

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  1. 1

    Fuel injector defect (recall 25S76 / NHTSA 25V467) reducing delivered fuel

    High severity

    The same recalled injector fault that caused rough idle and confirmed misfiring on this model can also under-deliver fuel and skew trims lean.

    Reported in 4 NHTSA complaints
    Parts:fuel injector
  2. 2

    Canister purge valve or EVAP solenoid stuck open (unmetered air leak)

    High severity

    Directly evidenced in this batch: a purge valve confirmed stuck open causing a hard start, and a separate owner who went through two EVAP solenoids for a recurring fuel-vapor-intake fault — both classic unmetered-air paths that read lean.

    Reported in 2 NHTSA complaints
    Parts:purge valveEVAP solenoid
  3. 3

    Vacuum or intake air leak (general)

    Medium severity

    Unmetered air entering downstream of the MAF sensor is the most common general cause of a lean-bank code.

    Common cause
  4. 4

    Dirty or failing MAF sensor

    Medium severity

    An under-reporting MAF sensor causes the ECM to add too little fuel, producing a lean condition.

    Common cause
    Parts:MAF sensor
  5. 5

    Weak fuel pump or clogged fuel filter

    Medium severity

    Reduced fuel delivery pressure under load is a common contributor to a lean-bank code.

    Common cause
    Parts:fuel pumpfuel filter
  6. 6

    Intake manifold gasket leak

    Medium severity

    A leaking manifold gasket is a classic unmetered-air source producing a persistent lean condition.

    Common cause
    Parts:intake manifold 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

1

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.

2

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.

3

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.

4

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.

5

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