P0171 on a 2013 Nissan Sentra

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 2013 Nissan Sentra

Ranked from 638 NHTSA owner complaints filed for this vehicle.

Sort by:

1
Mass Air Flow (MAF) Sensor Failure / Dirty MAF
Medium severity
A dirty or failing MAF sensor misreports the amount of air entering the engine, causing a lean condition. Look for erratic idle, stalling, and poor acceleration.
Reported in 2 NHTSA complaints
2
Failing Oxygen (O2) Sensor (Upstream)
Low severity
A faulty upstream O2 sensor can falsely report a lean condition or fail to properly adjust the air/fuel ratio. Confirmed by monitoring live O2 sensor voltage data.
Reported in 1 NHTSA complaint
3
Vacuum Leaks (Intake Manifold Gasket, Vacuum Hoses)
Medium severity
Unmetered air entering the engine after the MAF sensor causes a lean mixture. Look for cracked hoses, hissing sounds, or a degraded intake manifold gasket.
Common cause
4
Low Fuel Pressure (Failing Fuel Pump or Clogged Filter)
High severity
Insufficient fuel delivery to the injectors creates a lean mixture. Confirmed by testing fuel pressure at the rail.
Common cause
5
Clogged or Dirty Fuel Injectors
Medium severity
Restricted fuel injectors cannot deliver the commanded amount of fuel, leading to a lean condition. Confirmed by injector balance testing or cleaning.
Common cause
6
Exhaust Leak (Before Upstream O2 Sensor)
Medium severity
An exhaust leak allows outside air to reach the O2 sensor, tricking it into reading a lean condition. Look for soot or listen for ticking noises near the exhaust manifold.
Common cause

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