Honda Check Engine Code
P0171 on Honda
System Too Lean (Bank 1)
Also covers: Acura
P0171 on Honda: what makes it different
P0171 — System Too Lean, Bank 1 — is a very commonly reported code on Honda vehicles. Honda's VTEC-equipped four-cylinder engines and V6s are sensitive to vacuum leaks, dirty throttle bodies, and fuel delivery problems that push the fuel trim lean. The code appears frequently on Accord, Civic, CR-V, and Odyssey models, often linked to Honda-specific design elements such as the intake manifold gasket, idle air control passages, and PCV system.
Most-affected engines
- K24A/K24Z 2.4L i-VTEC (Accord, CR-V, Element)
- J30A/J35A 3.0L–3.5L V6 (Accord, Odyssey, Pilot)
- R18A 1.8L (Civic 2006–2011)
- K20A/K20Z 2.0L i-VTEC (Civic Si, RSX)
- F23A 2.3L SOHC VTEC (Accord 1998–2002)
Common model years: 1998–2020
Most likely cause on Honda
Vacuum leak at a cracked or disconnected intake manifold gasket or PCV hose, causing unmetered air to enter the intake manifold and lean out the air-fuel mixture.
Known Honda engine-family issues
Honda K-series engines (K20, K24) use a large PCV hose that routes from the valve cover to the intake manifold. This hose is made of rubber and becomes brittle and cracks after 8–10 years, creating a significant vacuum leak that is sometimes difficult to see by eye. Spraying carburetor cleaner around the hose while the engine idles is a fast way to locate the leak — idle speed will briefly change when the spray contacts the crack. Honda J35 V6 engines in the Odyssey are also well-known for developing P0171 and P0174 together due to a combination of fuel injector deposits and a crack in the intake plenum area over time.
Honda-specific causes (most common first)
- Cracked or deteriorated PCV hose or breather tube on K-series and J-series engines allowing unmetered air into the intake
- Vacuum leak at the intake manifold gasket, which hardens and cracks over time on high-mileage Honda four-cylinders
- Dirty or stuck IACV (Idle Air Control Valve) on older D-series and F-series engines causing lean idle conditions
- Clogged or dirty fuel injectors causing insufficient fuel delivery, common on higher-mileage Honda V6 Odyssey and Pilot
- Weak or failing fuel pump on high-mileage Accord and Odyssey not maintaining adequate rail pressure
- Dirty mass airflow sensor or MAP sensor giving an inaccurate airflow reading and causing the ECM to under-fuel
Honda-specific diagnostic tip
On a Honda with P0171, pull up short-term and long-term fuel trims on a scan tool at idle and at 2,500 RPM. If LTFT is over +10% at idle but drops back toward zero at higher RPM, the likely cause is a vacuum leak (leaks have a proportionally larger effect at low throttle). If LTFT stays elevated at all RPMs, suspect a fuel delivery problem such as weak injectors or a failing fuel pump. This RPM-based fuel trim analysis quickly separates vacuum leaks from fuel supply issues without any disassembly.
Symptoms drivers report
- Check engine light
- Rough idle, sometimes surging
- Hesitation on acceleration
- Reduced fuel economy
- Occasional misfires (P0300-series)
Typical repair cost on Honda
Most Honda owners fix P0171 for between $50 and $500, depending on which underlying cause turns out to be at fault. Start with the most-likely cause for your vehicle — Vacuum leak at a cracked or disconnected intake manifold gasket or PCV hose, causing unmetered air to enter the intake manifold and lean out the air-fuel mixture. — before throwing parts at it.
Honda P0171 FAQ
My Honda Accord has P0171 — could it just be a dirty air filter?
A severely clogged air filter can restrict airflow and affect MAF sensor readings, but it typically causes a rich condition, not lean. P0171 on an Accord is much more likely to be a vacuum leak or a dirty MAF sensor. Check the PCV hose and intake manifold area first.
Can I drive my Honda with P0171?
You can drive it short distances, but running lean long-term can cause increased engine temperatures, potential catalytic converter damage, and accelerated wear on combustion components. Resolve it within a few hundred miles.
P0171 and P0174 together on my Honda Odyssey — what does that mean?
P0171 (Bank 1 lean) together with P0174 (Bank 2 lean) on a J35 V6 Odyssey typically points to a large common-source vacuum leak or a fuel delivery problem affecting both banks equally, such as a failing fuel pump, a cracked intake plenum, or a dirty MAF sensor. Individual bank causes like a single injector are less likely when both banks show lean simultaneously.
Related codes
Drive a different make? See the general P0171 guide for cross-vehicle causes and symptoms.
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Most common fix for P0171:
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