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P0171

P0171 on a 2011 Volkswagen Jetta

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 2011 Volkswagen Jetta

Ranked from 639 NHTSA owner complaints filed for this vehicle.

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  1. 1

    Weak or failing high-pressure fuel pump (diesel)

    High severity

    Multiple owners of this TDI report the high-pressure fuel pump and fuel lines failing, a documented pre-2013 diesel Jetta issue that reduces fuel delivery and can produce a lean-running condition.

    Reported in 3 NHTSA complaints
    Parts:fuel pump
  2. 2

    Intake manifold gasket leak

    Medium severity

    One owner had to replace the intake manifold shortly before catalytic converter and fuel-system work, consistent with an unmetered-air leak at the manifold gasket.

    Reported in 1 NHTSA complaint
  3. 3

    Failing MAF or MAP-type sensor

    Medium severity

    One owner's scan returned a P0106 (manifold pressure/barometric sensor) code alongside driveability issues after a MAP sensor swap only temporarily fixed it, showing this air/pressure-sensing circuit is a real weak point on this platform.

    Reported in 1 NHTSA complaint
    Parts:manifold pressure sensor
  4. 4

    EGR valve fault affecting air/fuel metering

    Low severity

    One complaint reports the EGR getting stuck open/closed on this exact vehicle, which can skew the air charge the PCM assumes it's getting.

    Reported in 1 NHTSA complaint
    Parts:EGR valve
  5. 5

    Vacuum or intake air leak

    Medium severity

    Unmetered air past the MAF/MAP sensor is the most common cause of a bank-1 lean code; check intake boots and connections.

    Common cause
  6. 6

    Stuck-open PCV valve

    Low severity

    Excess unmetered air pulled through the crankcase vent leans the idle mixture.

    Common cause
    Parts:PCV valve
  7. 7

    Exhaust leak upstream of the front O2 sensor

    Medium severity

    Outside air reaching the sensor through a manifold leak causes it to read falsely 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

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