P0171 on a 2018 Hyundai Santa Fe Sport

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 Hyundai Santa Fe Sport

Ranked from 414 NHTSA owner complaints filed for this vehicle.

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1
Weak or failing fuel pump
Medium severity
This vehicle's owner reported the fuel pump had already been replaced among a string of engine-management repairs; a pump that can't hold pressure under load leans out the mixture.
Reported in 1 NHTSA complaint
Parts:fuel pump
2
Incomplete idle/fuel-trim relearn after ECU reflash (Service Campaign 9C2)
Medium severity
One owner reports severe stalling and surging that began immediately after a dealer software update, suggesting an incomplete adaptive relearn that can manifest as fuel-trim faults.
Reported in 1 NHTSA complaint
3
Vacuum or intake air leak
Medium severity
Unmetered air entering after the MAF sensor is the single most common cause of a lean (P0171) code.
Common cause
4
Dirty or failing MAF sensor
Medium severity
A contaminated or drifting MAF under-reports incoming airflow, causing the PCM to under-fuel.
Common cause
Parts:mass airflow sensor
5
Stuck-open PCV valve
Low severity
A PCV valve stuck open pulls excess crankcase air into the intake, leaning the mixture at idle.
Common cause
Parts:PCV valve
6
Intake manifold gasket leak
Medium severity
A leaking manifold gasket admits unmetered air downstream of the MAF, producing a persistent lean trim.
Common cause
Parts:intake manifold gasket
7
Exhaust leak upstream of the front O2 sensor
Low severity
Fresh air drawn in through an exhaust leak ahead of the sensor falsely reads as excess oxygen, pushing fuel trim 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