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P0171

P0171 on a 2010 Chevrolet Hhr

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 2010 Chevrolet Hhr

Ranked from 515 NHTSA owner complaints filed for this vehicle.

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  1. 1

    Corroded/rusted external steel fuel supply line leaking fuel

    High severity

    The overwhelming majority of this vehicle's complaints describe the factory steel fuel line rotting through near the rear wheel (a well-documented HHR/Cobalt defect under NHTSA investigation), which drops fuel rail pressure — especially at highway speed/high demand — and can pull the mixture lean.

    Reported in 28 NHTSA complaints
    Parts:fuel line
  2. 2

    Failing high-pressure fuel pump (secondary to the leak)

    Medium severity

    One owner's mechanic found the fuel pump had failed, attributed to the ongoing fuel-line leak dropping system pressure.

    Reported in 1 NHTSA complaint
    Parts:fuel pump
  3. 3

    Vacuum or intake leak

    Medium severity

    Cracked hose, PCV line, or brake booster line lets in unmetered air.

    Common cause
  4. 4

    Dirty or failing MAF sensor

    Medium severity

    Under-reports airflow so the PCM commands less fuel than needed.

    Common cause
    Parts:mass airflow sensor
  5. 5

    Clogged fuel filter

    Low severity

    Restricted filter drops rail pressure under demand, same symptom as the line leak.

    Common cause
    Parts:fuel filter
  6. 6

    Stuck-open PCV valve

    Low severity

    Constant extra air bleeds into the intake, leaning the mixture.

    Common cause
    Parts:PCV valve
  7. 7

    Exhaust leak upstream of the front O2 sensor

    Medium severity

    Draws in outside air, making the sensor read falsely lean.

    Common cause
  8. 8

    Intake manifold gasket leak

    Medium severity

    Common on aging GM Ecotec engines; introduces unmetered air.

    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