P0171 on a 2019 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 2019 Volkswagen Jetta

Ranked from 541 NHTSA owner complaints filed for this vehicle.

Sort by:

1
Cracked EVAP purge line or stuck-open purge valve (vacuum leak)
Medium severity
Owners reported a cracked canister-purge hose and a dealer-confirmed defective purge valve on this same vehicle/engine, both of which act as an unmetered vacuum leak that leans the mixture.
Reported in 2 NHTSA complaints
Parts:purge valve
2
Weak fuel pump delivery
High severity
One owner's engine stumbled and stalled and was repaired with a fuel pump and fuel feed system replacement, consistent with insufficient fuel pressure causing a lean condition under load.
Reported in 1 NHTSA complaint
Parts:fuel pump
3
Vacuum or intake leak
Medium severity
A cracked hose or loose boost/intake fitting adds unmetered air the ECM can't account for.
Common cause
4
Dirty or failing MAF sensor
Medium severity
An underreporting MAF causes the ECM to under-fuel across the board; cleaning or replacement and freeze-frame review confirms it.
Common cause
Parts:mass air flow sensor
5
Clogged fuel filter
Medium severity
Restricted fuel flow under load produces a lean trim that worsens with throttle demand.
Common cause
Parts:fuel filter
6
Stuck-open PCV valve
Low severity
Excess crankcase air admitted through a stuck PCV valve leans the idle mixture.
Common cause
Parts:PCV valve
7
Exhaust leak upstream of the front O2 sensor
Medium severity
Outside air pulled in through a manifold or turbo-downpipe leak fools the upstream sensor into reading 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

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