P0171 on a 2016 Nissan Altima
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 2016 Nissan Altima
Ranked from 548 NHTSA owner complaints filed for this vehicle.
- 1
Failing air-fuel ratio (A/F) sensor
Medium severityOne owner's vehicle was in for repair 10 times with diagnostic codes always pointing to the A/F sensor, referencing multiple Nissan service bulletins — a documented cause of incorrect fuel-trim/lean readings on this platform.
Reported in 1 NHTSA complaintParts:air fuel ratio sensor - 2
Mass airflow sensor fault / intake manifold vacuum leak
Medium severityMAF sensor and intake manifold were replaced by an independent shop after failure symptoms, referencing Nissan TSB NTB16-121a.
Reported in 1 NHTSA complaint - 3
Vacuum or intake leak
Medium severityCracked hose or loose clamp lets in unmetered air.
Common cause - 4
Weak fuel pump or clogged fuel filter
Medium severityInsufficient rail pressure under demand pulls the mixture lean.
Common cause - 5
- 6
Exhaust leak upstream of the O2 sensor
Medium severityDraws in outside air, making the sensor read falsely lean.
Common cause
Part links go to Amazon search results for this vehicle. As an Amazon Associate, WrenchConnect earns from qualifying purchases — always confirm fitment for your exact trim and engine before ordering.
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.