P0171 on Honda: How to Diagnose & Fix
System Too Lean (Bank 1)
7 Honda models · 10 documented issues · 5 critical · $20-$3,500 repair
P0171 on Honda by model: symptoms, diagnosis and fix
Gasoline mixes with engine oil in the 1.5L turbocharged engine, causing the oil level to rise above the full mark. The issue is most prevalent in cold climates where short trips don't allow the engine to reach full operating temperature. Unburned fuel bypasses the piston rings and enters the crankcase, diluting the oil and reducing its lubricating properties.
Common Symptoms
- Oil level reading above full mark on dipstick
- Strong gasoline smell from engine oil
- Check engine light illumination
- Reduced engine power
- Engine stalling
- Poor fuel economy
How to Fix
Honda released a software update for the engine and transmission control units (with an oil change, and in some cases a replacement A/C control unit) to help the engine warm up faster in cold conditions. For 2017-2018 models, Honda also extended warranty coverage on the camshaft, rocker-arm assemblies and spark plugs by one year, to 6 years from purchase with unlimited miles. Owners should change oil more frequently (every 3,000-5,000 miles) in cold climates.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Genuine Honda 15400-PLM-A02 engine oil filterOEMHonda 15400-PLM-A02
Oil-filter consumable when an owner performs the shorter oil-change interval described by the repair guidance Fitment/availability: 2017-2023 U.S. CR-V 1.5T within this record; cataloged broadly for the CR-V and shown specifically for th…
Owner tips & cautions
- WarningThis is a high-severity issue - ignoring it can lead to costly repairs or safety concerns. Address it promptly.
- TipGet a proper diagnosis before replacing parts - similar symptoms can have different causes
- TipSearch Honda CR-V forums and owner groups for real-world experiences and DIY guides
- TipGet multiple quotes from independent mechanics - dealer prices can be 2-3x higher for the same repair
Sources for this issue (4)
Variable Cylinder Management (VCM) deactivates 3 rear cylinders during light load, but insufficient pressure allows oil to bypass the piston rings into the combustion chamber. Causes excessive oil consumption (1 quart per 1,000 miles), fouled spark plugs, catalytic converter damage, and premature piston ring wear. Honda settled a class-action lawsuit over the problem.
Common Symptoms
- Excessive oil consumption (1 qt per 1,000 miles or more)
- Engine misfire codes (P0300-P0304, typically cylinders 1-4)
- Fouled/oil-soaked spark plugs
- Rough idle and vibration
- Check engine light (misfire and catalyst codes)
- White smoke from exhaust on startup
- Failed catalytic converters (P0420/P0430)
How to Fix
Install VCM disable device (VCMuzzler, VCMTuner) which prevents cylinder deactivation and stops oil consumption. Replace fouled spark plugs after installing disabler. Honda settled a class action (Soto v. American Honda) covering 2008-2013 Odyssey with an 8-year warranty extension for engine misfire repairs, and announced a further warranty extension in June 2025 for certain 2013-2017 Odyssey. Severe cases may require piston ring replacement ($3,000-$5,000). 2014-2017 models still use VCM.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Genuine Honda/NGK 9807B-5517W IZFR5K11 spark plug, eachOEMHonda 9807B-5517W / NGK IZFR5K11
Early-generation plug branch only after inspection identifies a fouled plug and exact catalog application Fitment/availability: 2005-2007 U.S. Honda Odyssey 3.5L applications in this issue; Honda catalogs 9807B-5517W across 2005-2010 but…
- Genuine Honda/NGK 12290-R70-A01 ILZKR7B11 spark plug, eachOEMHonda 12290-R70-A01 / NGK ILZKR7B11
VCM plug-fouling branch after code and plug inspection identifies replacement Fitment/availability: 2008-2010 U.S. Honda Odyssey EX-L/Touring with VCM; select 12290-R70-A01.
- Genuine Honda/NGK 12290-R71-L01 DILZKR7A11G spark plug, eachOEMHonda 12290-R71-L01 / NGK DILZKR7A11G
Fourth-generation plug-fouling branch after P0301-P0304 and physical plug diagnosis Fitment/availability: 2011-2017 U.S. Honda Odyssey all trims; sold individually and six are required for a full set.
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Owner tips & cautions
- TipCheck oil level every fuel fill-up on VCM-equipped models - carry a quart of oil in the van
- WarningDon't ignore misfire codes - prolonged misfires destroy catalytic converters ($2,000+ repair)
Sources for this issue (2)
Variable Cylinder Management (VCM) causes excessive oil consumption (1 quart every 1,000-1,500 miles), engine misfires, and fouled spark plugs. The reciprocating effect creates vacuum that pulls oil past piston rings. Leads to premature failure of spark plugs, catalytic converters, engine mounts, and cylinder walls. The 2013 VCM class-action settlement (8-year warranty extension) covered only 2009-2013 Pilots, not these model years.
Common Symptoms
- Excessive oil consumption (1 qt per 1,000-1,500 miles)
- Engine misfires (P0300-P0306 codes)
- Fouled spark plugs
- Rough idle or hesitation
- Check engine light
- Excessive engine vibration when VCM activates
- Blue smoke from exhaust
How to Fix
Disable VCM using aftermarket devices: VCMuzzler II ($81), VCMTuner II ($150-200), or S-VCM Controller ($180-250). Check oil level every 500-1,000 miles and top off as needed. Use synthetic 0W-20 oil. Replace spark plugs every 30k-50k miles instead of 100k. Severe cases may need engine rebuild ($4,000-$8,000).
Owner tips & cautions
- TipDisabling VCM reduces damage to engine mounts ($800) and minimizes transmission torque converter wear
- TipCheck oil level every 500-1,000 miles and keep 2-3 quarts of oil in vehicle for top-offs
- WarningDo not ignore excessive oil consumption - running engine low on oil can cause catastrophic engine failure
Sources for this issue (2)
The 8th generation Accord V6 (3.5L J35Z2) with Variable Cylinder Management (VCM) deactivates 3 cylinders at highway speeds, causing excessive oil consumption (1 quart per 1,000-1,500 miles), misfires, and accelerated engine vibration that damages engine mounts. When VCM deactivates cylinders, insufficient ring pressure allows oil to bypass rings into combustion chamber. The class action lawsuit (Soto v. American Honda, filed 2012) covered about 1.6 million VCM vehicles. Honda settled in 2013, providing an 8-year, unlimited-mileage extended warranty for repairs related to VCM-caused misfires and spark plug fouling. Many owners in the Drive Accord community disable VCM immediately upon purchase.
Common Symptoms
- Oil level dropping about 1 quart every 1,000-1,500 miles
- Engine misfires (P0300-P0306 codes)
- Fouled spark plugs with carbon and oil deposits
- Excessive vibration felt through steering wheel and seats
- Check engine light with misfire and/or catalyst codes
- Catalytic converter efficiency codes (P0420, P0430)
- Blue smoke from exhaust at startup
How to Fix
Install VCM disabler device: VCMuzzler II (~$81, simplest install, no power wire), VCMTuner II ($150-200, more features), or S-VCM Controller ($180-250, automatic temperature adjustment). Check oil every 500-1,000 miles until VCM disabled. Replace fouled spark plugs with NGK DILKAR7B11 ($5-8 each) every 30,000-50,000 miles. Honda's 2013 class action settlement provided an 8-year extended warranty for misfires with fouled plugs - contact Honda with VIN (the 8-year term has now run out on most cars). Severe cases (catalytic converters destroyed): $2,000-3,500 replacement.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- VCMuzzler II VCM suppression deviceOEMVCMuzzler II
Optional owner-selected VCM suppression after understanding the device's operating tradeoffs Fitment/availability: 2008-2012 Accord V6 automatic only; vendor explicitly excludes manual-transmission Accord. Select model year, model and pi…
- S-VCM ControllerOEMS-VCM Controller
Confirm connector/application with vendor.
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Sources for this issue (2)
The 1.5L turbocharged Earth Dreams direct-injection engine (L15B7) accumulates heavy carbon deposits on intake valves and ports because fuel is injected directly into the cylinder, bypassing the intake valves. Unlike port-injection engines, no fuel washes the intake valves clean. Owners report symptoms beginning at 40,000-60,000 miles. Carbon buildup restricts airflow, causing rough idle, misfires, reduced power, and reduced fuel economy. This is inherent to direct-injection technology and affects all 10th-gen Civic 1.5T variants.
Common Symptoms
- Rough idle or stumbling at idle
- Misfires on cold start (P0300-P0304)
- Hesitation or stumbling during acceleration
- Reduced power output compared to new
- Decreased fuel economy (2-4 mpg reduction)
- Hard cold starts
- Occasional rough running that improves when warm
How to Fix
Walnut blasting (walnut shell media blast cleaning) of intake valves every 40,000-60,000 miles is the industry-standard solution: $300-500 at independent shops, $500-800 at dealers. Chemical intake cleaners (CRC GDI IVD Intake Valve Cleaner #05319, Liqui-Moly Valve Clean) used every 10,000 miles can slow buildup but do not fully remove existing deposits. Top-tier gasoline (Shell V-Power, Chevron Techron) contains detergent additives that help prevent buildup. Catch-can installation ($80-150) reduces oil vapor contributing to buildup.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- CRC GDI IVD Intake Valve & Turbo Cleaner 05319, 11 ozOEMCRC 05319
Manufacturer-directed chemical cleaning option for diagnosed or suspected light-to-moderate GDI intake deposits Fitment/availability: 2016-2021 Civic 1.5T only after ruling out bulletin/software, injector, ignition, boost and mechanical …
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Owner tips & cautions
- TipCivicX.com consensus: Schedule walnut blast cleaning at 50,000 miles regardless of symptoms - visible buildup starts at 40k miles and only gets worse. Independent shops charge $300-400 vs dealer $600+
Sources for this issue (3)
Owners of 11th-generation Civics (2022 and later) have filed NHTSA complaints that the Collision Mitigation Braking System (Honda's automatic emergency braking) braked hard, or sounded a forward-collision alarm, when nothing was close ahead. Forward collision avoidance is the most common complaint category for the 2022 Civic. One 2022 owner using adaptive cruise at 75 mph reported about two seconds of braking with no pedal input while the nearest car was at least a quarter mile away. A 2024 owner reported the car stopping abruptly with no vehicles or objects nearby at 8,000 miles, and the dealer could not find a cause. Complaint mirrors list 11 forward-collision complaints for the 2022 Civic (3 involving a crash and 4 an injury), 34 for 2023 and 2 for 2024. Other owners describe a collision mitigation system warning that appears at random or at startup, sometimes turning off adaptive cruise and lane keeping until it clears. The 11th-generation Civic runs Honda Sensing from a single forward-facing camera. It has no front radar, which Honda's earlier camera-and-radar system and other Honda models use. NHTSA's inadvertent-braking investigation (PE22-003, upgraded to EA24-002 and closed on April 18, 2024 with no recall) covered the Accord and CR-V, not the Civic. We found no recall or Civic-specific service bulletin for false braking. On the 1.5L turbo, owner reports describe fuel in the oil (oil dilution) rather than proven oil burning. A 2022 Civic Si owner reported a gasoline smell in the oil and asked whether a recent cold snap caused it. With direct injection, unburned fuel can get past the piston rings into the oil. Short trips that never fully warm the engine make this worse, and owners who report it have usually lived in colder climates. One forum member said he had seen no evidence either way for the 11th-gen engine, and an owner-review roundup found dilution reports only a handful of times. We found no consumption figure or Honda bulletin specific to the 11th-gen 1.5T.
Common Symptoms
- Automatic emergency braking applies hard with no vehicle or object close ahead
- Sudden braking at highway speed while using adaptive cruise control
- Forward Collision Warning alarm with nothing nearby
- Collision mitigation system warning at random or at startup, sometimes turning off adaptive cruise and lane keeping
- 1.5T: gasoline smell in the oil
How to Fix
False braking or warnings: Write down when it happens (adaptive cruise on or off, speed, weather, what was ahead) and any dashboard message. One owner said a dealer told them the alarm can trigger in hard rain. Because the 2022+ Civic's forward braking runs off a single windshield camera, if the windshield or camera has been serviced, make sure the shop followed Honda's repair procedure. Ask a Honda dealer to diagnose the collision mitigation system. Owners report that dealers often cannot find a cause or reproduce the problem, so bring your notes or a dashcam clip. We found no recall, warranty extension or Civic-specific bulletin for this. If the car brakes on its own, file a complaint with NHTSA. The investigation into the Accord and CR-V was built from more than 1,000 owner complaints like these. 1.5T fuel-in-oil: Check the dipstick regularly for a gasoline smell. Short trips in cold weather make dilution worse, so drives long enough to fully warm the engine help. Honda's interval is 7,500 miles, but mechanics quoted in an owner-review roundup suggest changing the oil about every 5,000 miles if you are dealing with dilution. If the oil level is actually dropping, keep dated mileage and dipstick records before asking the dealer for an oil-consumption check.
Call to confirm they can assess your vehicle and perform the stated work. Search results do not confirm qualification, eligibility or coverage.
Owner tips & cautions
- TipCivicX.com 11th gen owners: Document EVERY oil check with date, mileage, and amount added - Honda requires formal consumption test documented over 1,000 miles to approve warranty engine work
- TipFor phantom braking: Reference NHTSA investigation PE22-029 when requesting Honda Sensing recalibration at dealer - shows Honda the federal investigation and often results in free repairs beyond warranty
- WarningPhantom braking at highway speeds is extremely dangerous - document all incidents with GPS location, time, weather conditions and file NHTSA complaint at nhtsa.gov; this is how recalls get initiated
Sources for this issue (9)
- NHTSA Vehicle Page for 2022 Honda Civic - owner complaints incl. automatic emergency brakingnhtsa
- 2022 Honda Civic forward collision avoidance warnings complaints (NHTSA mirror)complaint-aggregate
- 2023 Honda Civic forward collision avoidance complaintscomplaint-aggregate
- 2024 Honda Civic forward collision avoidance complaintscomplaint-aggregate
- 2022 Honda Civic problems and complaintsarticle
- Honda eliminates radar unit on new Civicarticle
- NHTSA PE22-003 / EA24-002 inadvertent automatic emergency brakinginvestigation-summary
- CivicXI forum: Oil fouling issue in 1.5L turboforum
- How reliable is Honda's 1.5L turbo engine? Owner reviewsarticle
P0171 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0171 mean on a Honda?
P0171 stands for "System Too Lean (Bank 1)." This code means the engine's computer has detected that the air-fuel mixture on Bank 1 (the side of the engine with cylinder #1) is running too lean — meaning there is too much air relative to fuel. The computer watches the oxygen sensors and has had to add a large amount of extra fuel (long-term fuel trim) to try to compensate, but it has hit its correction limit. A lean condition can cause rough idle, hesitation, reduced power, and over time can run the engine hotter than normal. It usually points to either unmetered air leaking into the engine or not enough fuel being delivered. On Honda it is documented across 7 models: CR-V, Odyssey, Pilot, Accord, Civic, Fit, Insight.
What are the most common causes of P0171?
The most common causes of P0171 are: Vacuum or intake air leak (cracked hose, gasket, or PCV system), Dirty or failing mass airflow (MAF) sensor, Weak fuel pump or restricted fuel filter, Clogged or dirty fuel injectors, Faulty or aged upstream oxygen sensor, Leaking intake manifold gasket, Low fuel pressure or failing fuel pressure regulator, Exhaust leak ahead of the oxygen sensor. The specific cause varies by vehicle.
How much does it cost to fix P0171 on a Honda?
Published repair estimates on Honda range from $20 to $3,500 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.