P0171 on a 2013 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 2013 Honda Accord

Ranked from 1,418 NHTSA owner complaints filed for this vehicle.

Sort by:

1
Low Fuel Pressure (Failing Fuel Pump or Clogged Filter)
High severity
Insufficient fuel delivery causes a lean condition. Confirmed by testing fuel pressure at the rail; complaints note high-pressure fuel pump failures and stalling.
Reported in 2 NHTSA complaints
2
Vacuum Leak (Intake Manifold, Vacuum Hoses, PCV System)
Medium severity
Unmetered air entering the engine leans out the air/fuel mixture. Look for cracked or disconnected vacuum hoses, a leaking intake manifold gasket, or a faulty PCV valve.
Common cause
3
Faulty Mass Air Flow (MAF) Sensor
Medium severity
A dirty or failing MAF sensor incorrectly measures incoming air, causing the PCM to inject less fuel than needed. Confirmed by checking MAF sensor data on a scan tool.
Common cause
4
Clogged or Faulty Fuel Injectors
Medium severity
Restricted injectors cannot deliver the commanded amount of fuel, leading to a lean mixture. Confirmed by injector balance testing or observing fuel trims.
Common cause
5
Faulty Oxygen (O2) Sensor or Air/Fuel Ratio Sensor
Medium severity
A degraded upstream O2 sensor may falsely report a lean condition or fail to properly monitor the mixture. Confirmed by observing sensor voltage response.
Common cause
6
Exhaust Leak Before the Upstream O2 Sensor
Medium severity
Outside air drawn into the exhaust stream is read by the O2 sensor as a lean condition. Look for cracked exhaust manifolds or leaking gaskets.
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