P0171 on a 2018 Honda Pilot

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 2018 Honda Pilot

Ranked from 427 NHTSA owner complaints filed for this vehicle.

Sort by:

1
Fuel pump failure (low-pressure pump recall / high-pressure pump failure)
High severity
This model/year is under an active Honda fuel-pump recall (swelling motor impeller); multiple owners report the pump failing or the recall replacement itself later failing, starving fuel delivery and driving the mixture lean.
Reported in 5 NHTSA complaints
Parts:fuel pump
2
Fuel injector fouling/failure
Medium severity
Owners report failed or contaminated fuel injectors alongside the fuel-pump recall, reducing/uneven fuel delivery.
Reported in 2 NHTSA complaints
Parts:fuel injectors
3
Vacuum or intake air leak
Medium severity
Unmetered air past the MAF is a common lean-code cause; smoke-test intake boots and vacuum lines.
Common cause
4
Dirty or failing MAF sensor
Medium severity
An under-reporting MAF under-fuels the engine.
Common cause
Parts:mass airflow (MAF) sensor
5
Stuck-open PCV valve
Low severity
Excess unmetered crankcase air leans the mixture, especially at idle.
Common cause
Parts:PCV valve
6
Exhaust leak upstream of the O2 sensor
Medium severity
Outside air drawn in ahead of the sensor skews it toward a false lean reading.
Common cause
7
Intake manifold gasket leak
Medium severity
A leaking gasket admits unmetered air directly into the manifold.
Common cause
Parts:intake manifold gasket

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.

Matching symptoms

Car Runs Rough