P0171 on a 2017 Honda Accord

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 2017 Honda Accord

Ranked from 527 NHTSA owner complaints filed for this vehicle.

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1
Clogged or Failing Fuel Injectors
High severity
Fuel injectors can become clogged or fail, leading to a lean condition (P0171) and causing hesitation, stalling, or loss of power. Look for misfire codes (like P0302) or loss of motive power.
Reported in 5 NHTSA complaints
2
Failing Fuel Pump
High severity
A failing fuel pump or low fuel pressure can cause a lean condition, leading to stalling, hesitation, or failure to start. Confirm by checking fuel pressure and looking for stalling symptoms.
Reported in 5 NHTSA complaints
3
Vacuum Leak
Medium severity
Unmetered air entering the intake manifold after the MAF sensor causes a lean mixture. Look for cracked hoses, a loose intake manifold, or listen for a hissing sound.
Common cause
4
Faulty Mass Air Flow (MAF) Sensor
Medium severity
A dirty or faulty MAF sensor can under-report the amount of air entering the engine, causing the PCM to inject less fuel. Confirm by checking MAF sensor readings on a scan tool.
Common cause
5
Exhaust Leak Before the O2 Sensor
Medium severity
An exhaust leak upstream of the primary oxygen sensor can introduce oxygen into the exhaust stream, tricking the sensor into reading a lean condition. Look for soot marks or listen for exhaust ticking.
Common cause
6
Faulty Primary Oxygen (O2) Sensor or Air/Fuel Ratio Sensor
Medium severity
A degraded or failing upstream O2 sensor can falsely report a lean condition to the PCM. Confirm by monitoring sensor voltage/current data and fuel trims.
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