P0171 on a 2019 Honda Civic Hatch

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 Honda Civic Hatch

Ranked from 414 NHTSA owner complaints filed for this vehicle.

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1
Weak/failing fuel pump (impeller degradation — NHTSA recall 23V-858)
High severity
The recalled fuel pump impeller deforms over time and reduces fuel delivery/pressure, producing exactly the stalling, hard-start, and power-loss pattern reported by numerous owners still waiting on the recall part.
Reported in 11 NHTSA complaints
Parts:fuel pump
2
Failing or clogged fuel injector
Medium severity
One owner reports a fuel injector failure at 58,000 miles that Honda has acknowledged as a widespread parts-quality issue, restricting fuel delivery on that cylinder.
Reported in 1 NHTSA complaint
Parts:fuel injector
3
Vacuum or intake leak
Medium severity
Unmetered air entering after the MAF sensor skews the fuel trim lean; smoke-test the intake boots, PCV hose, and brake booster line.
Common cause
4
Dirty or failing MAF sensor
Medium severity
An under-reporting MAF causes the PCM to add too little fuel; inspect for contamination and compare readings to a scan-tool reference.
Common cause
Parts:mass airflow sensor
5
Stuck-open PCV valve
Low severity
A PCV valve stuck open pulls in excess unmetered air, especially at idle; check for a rough/lean idle and PCV valve rattle.
Common cause
Parts:PCV valve
6
Intake manifold gasket leak
Medium severity
A leaking gasket admits unmetered air downstream of the throttle body, causing a persistent lean condition; check with propane or smoke around the manifold.
Common cause
Parts:intake manifold gasket
7
Exhaust leak upstream of the front O2/air-fuel sensor
Low severity
Outside air drawn in through an exhaust leak fools the upstream sensor into reading lean; inspect the manifold and head-pipe joints.
Common cause
8
Clogged fuel filter or restricted fuel supply
Low severity
Reduced fuel flow lowers rail pressure under demand, mimicking the same lean condition as a weak pump; check fuel pressure under load.
Common cause
Parts:fuel filter

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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