P0171 on a 2018 Volkswagen Atlas

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 2018 Volkswagen Atlas

Ranked from 455 NHTSA owner complaints filed for this vehicle.

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1
EVAP purge valve stuck open (unmetered air)
Medium severity
One complaint on this exact vehicle describes the 'EVAP Purge High Flow Control' failing open and causing random stalling — a stuck-open purge valve behaves like a vacuum leak and pushes fuel trim lean.
Reported in 1 NHTSA complaint
Parts:purge valve
2
Stuck/failed PCV (breather) valve
Medium severity
One complaint on this vehicle documents a failed breather/PCV valve leaking oil into the intake/AC system, consistent with the unmetered-air path that causes lean codes.
Reported in 1 NHTSA complaint
Parts:PCV valve
3
Fuel pump or fuel pump control module fault
Medium severity
One complaint describes sudden loss of engine power attributed by the owner to the fuel pump control module/wiring, consistent with insufficient rail pressure causing lean trims.
Reported in 1 NHTSA complaint
Parts:fuel pump
4
Vacuum or intake air leaks
Medium severity
Unmetered air after the MAF skews fuel trim lean; smoke-test the intake tract and PCV/brake-booster hoses.
Common cause
5
Dirty or failing MAF sensor
Medium severity
An underreporting MAF causes under-fueling and a lean trim code, worse at higher airflow.
Common cause
Parts:MAF sensor
6
Exhaust leak upstream of the O2 sensor
Low severity
Outside air reaching the sensor before the exhaust is fully sampled falsely reads lean.
Common cause
7
Intake manifold gasket leak
Medium severity
A leaking gasket admits unmetered air directly into the affected bank, a classic bank-specific lean cause.
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

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