P0171 on a 2023 Honda Civic Sedan

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 2023 Honda Civic Sedan

Ranked from 251 NHTSA owner complaints filed for this vehicle.

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1
Wiring or harness damage (e.g., rodent chewing) disrupting MAF or O2 sensor circuits
Medium severity
One owner on this exact model reported rodent damage that compromised the emissions and acceleration systems; damaged sensor wiring can introduce a false lean signal.
Reported in 1 NHTSA complaint
Parts:wiring harness
2
Declining fuel economy/range consistent with an unmetered-air condition
Low severity
One owner reported the dash's estimated range on a full tank steadily dropping over time, a pattern consistent with the engine compensating for an unmetered-air leak.
Reported in 1 NHTSA complaint
3
Vacuum or intake leak (cracked hose, loose intake boot, or PCV hose)
Medium severity
The most common cause of a lean-bank code; unmetered air entering after the MAF sensor drives the fuel trim lean.
Common cause
Parts:vacuum hose intake boot
4
Failing or dirty mass airflow (MAF) sensor
Medium severity
An underreporting MAF sensor causes the PCM to command less fuel than the actual incoming air requires.
Common cause
Parts:MAF sensor
5
Weak fuel pump or clogged fuel filter
Medium severity
Reduced fuel delivery under load can't keep pace with airflow, causing the system to run lean.
Common cause
Parts:fuel pump fuel filter
6
Stuck-open PCV valve
Low severity
Unmetered air entering through a PCV system that won't close contributes to a lean condition.
Common cause
Parts:PCV valve
7
Exhaust leak upstream of the primary oxygen sensor
Medium severity
A leak ahead of the sensor draws in outside air and skews the reading toward lean.
Common cause
Parts:exhaust manifold gasket
8
Intake manifold gasket failure
Medium severity
A leaking intake gasket admits unmetered air, driving the fuel trim lean.
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