P0171: System Too Lean (Bank 1)
187 vehicles · 27 makes · $20-$15,000 repair
Most Reported On
P0171 is an OBD-II diagnostic trouble code meaning “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. This code is most commonly reported on 2004-2012 Mazda RX-8, 2008-2021 Volkswagen Golf (GTI, GTI Autobahn, GTI S, GTI SE, Golf R, R, R32), and 2017-2023 Honda CR-V (EX, EX-L, Sport, Sport Touring, Sport-L, Touring), plus 184 other vehicles, with repair costs ranging from $20 to $15,000.
Common Causes
Typical Repair Cost
Based on 242 documented vehicle-specific issues. Actual cost depends on root cause and vehicle.
Diagnostic Tools
To diagnose P0171, you'll need an OBD-II scanner. Here are our recommendations at every price point.
ANCEL AD310 Classic OBD-II Scanner
by ANCEL
A simple, affordable code reader that reads and clears check engine codes. Great for quick diagnostics on any OBD-II vehicle (1996+).
- Read & clear engine codes
- View freeze frame data
- I/M readiness status
- No batteries or app needed
BlueDriver Pro Bluetooth Scanner
by BlueDriver
Bluetooth OBD-II scanner with a free companion app. Provides enhanced diagnostics, smog readiness, and repair reports sourced from a database of verified fixes.
- Enhanced diagnostics (ABS, SRS, transmission)
- Repair Reports with verified fixes
- Smog check readiness
- Free app (iOS & Android)
LAUNCH CRP123X OBD-II Scanner
by LAUNCH
A professional-grade handheld scanner that reads all four major systems (engine, transmission, ABS, SRS) with live data streaming and graphing.
- Engine, transmission, ABS, SRS diagnostics
- Live data stream & graphing
- AutoVIN for vehicle identification
- Free lifetime updates via Wi-Fi
Autel MaxiCOM MK808S Diagnostic Tool
by Autel
Shop-level diagnostic tablet with bi-directional control, active tests, and full system coverage. Ideal for serious DIYers and small shops.
- All-system diagnostics (25+ modules)
- Bi-directional control & active tests
- Oil reset, EPB, BMS, TPMS, injector coding
- 7-inch touchscreen with Android OS
As an Amazon Associate, we earn from qualifying purchases. Prices are approximate and may vary.
Vehicles Affected (187)
Intake Valve Carbon Buildup
G80 S58 Engine Carbon Buildup on Intake Valves
S58 Intake Valve Carbon Buildup
S58 Intake Valve Carbon Buildup
MAF Sensor Degradation Causing Lean Codes, Hesitation, and Reduced Power
S63/S63TU Valve Stem Seal Failure & Oil Consumption
N63 Valve Stem Seal / Oil Consumption (xDrive50i)
S55 High-Pressure Fuel Injector Failure - F82/F83 M4
S63/S63TU Ignition Coil Premature Failure
N54 High Pressure Fuel Pump (HPFP) Failure - E89 Z4 sDrive35i/35is
Park Avenue 3800 V6 Lower Intake Manifold (LIM) Gasket Leak
LeSabre 3800 V6 Lower Intake Manifold (LIM) Gasket Leak
PCV / Camshaft Cover Diaphragm Failure (1.4L Turbo) - "Tea Kettle" Whistle
Excessive Oil Consumption (2.4L Piston Ring Defect)
Engine Oil Leak Fire Risk (Oil Filter Adapter)
1.4L Turbo PCV Valve Cover Diaphragm Failure
Intake Manifold Gasket Leak
Lower Intake Manifold Gasket Leak
Central Port Injection (Spider) Fuel Leak
Intake Manifold Gasket Coolant Leak
1.5L Turbo Intake Valve Carbon Buildup Causing Misfires and Rough Cold Start (GDI)
CSFI/CPI 'Spider' Fuel Injector Assembly Failure (Misfire, Rough Idle, Poor Fuel Economy)
5.3L Vortec Excessive Oil Consumption (Low-Tension Rings / PCV)
5.7L Vortec Spider Injector Assembly Failure (CPI)
High-Pressure Direct-Injection Fuel Pump Failure Causing Stalling and Limp Mode (1.5L Turbo)
4.3L V6 Intake Manifold Gasket Leak
In-Tank Fuel Pump Failure
4.3L Vortec Central Sequential Fuel Injection (CSFI) Failure
4.3L V6 Intake Manifold Gasket Leak
3.1L/3.4L V6 Intake Manifold Gasket Leak (Dex-Cool)
3.8L V6 Intake Manifold Gasket and Coolant Elbow Leak
Excessive Oil Consumption (2.5L Ecotec LCV/LKW)
Intake Manifold Gasket Leak (3.4L/3.8L V6)
4.3L V6 Intake Manifold Gasket Leak
Central Port Injection Fuel Leak Under Intake
3.6L V6 Direct-Injection Intake Valve Carbon Buildup
1.2L/1.3L Turbo Engine Oil Consumption
4.3L V6 CPI/CSFI "Spider" Fuel Injector Leaks and Poppet Valve Failure
5.3L Vortec 5300 (Gen IV LC9/LMG) Excessive Oil Consumption from Piston Rings/AFM
Broken Exhaust Manifold Bolts (Startup Ticking)
2.2L/2.4L Head Gasket Failure
PCV Valve Cover Failure and Oil Leak (1.4T)
CSFI 'Spider' Central Port Injector / Poppet Valve Failure (5.7L Vortec)
5.7L Vortec CSFI 'Spider' Poppet Injector Failure
Intake Manifold Gasket Vacuum Leak (Rough Idle, Cold-Start Misfire, Lean Codes)
Vortec Intake Manifold Gasket Leak (Vacuum/Oil)
CSFI "spider" poppet fuel injector failure (special coverage 99066F)
Lower intake manifold gasket coolant/vacuum leak (5.7L Vortec)
4.3L Vortec CSFI "Spider" Injector Poppet Valve Leaking/Clogging
Lower Intake Manifold Gasket Coolant/Oil Leak
CSFI/CPI "Spider" Fuel Injector Assembly Failure (Poppet Valve Leaks)
Chronic Overheating - Multiple Causes
2.4L Tigershark Excessive Oil Consumption
Cooling System Failures (3.3L/3.8L V6)
Head Gasket Failure (Especially Turbo Models)
Turbocharger Failure (GT/Turbo Models)
3.6L Pentastar Engine Stalling and Head Gasket Failure
3.5L V6 Head Gasket Failure and Overheating
5.9L Magnum Plenum Gasket Failure
Cooling System Failures (3.3L/3.8L V6)
2.4L DOHC Head Gasket Failure
2.4L MultiAir Excessive Oil Consumption
Engine Overheating - Thermostat Housing Debris
Plenum Gasket Failure (5.2L/5.9L Magnum V8)
Plenum Gasket Failure (5.2L/5.9L Magnum V8)
2.2L/2.5L Head Gasket Failure
Head Gasket Failure
5.2L/5.9L Engine Idle Surge and Hunting
2.4L Electronic Throttle Body Failure
2.2L/2.5L Head Gasket Failure
Gen 1 V10 Head Gasket Failure
Plenum Gasket Failure (5.2L/5.9L V8)
Intake Plenum Pan Gasket Failure (Magnum V6/V8) Causing Oil Consumption and Misfire
2.3L EcoBoost Head Gasket Failure and Coolant Intrusion
2.0L Direct Injection Carbon Buildup on Intake Valves
1.5L EcoBoost Coolant Intrusion into Cylinders - Engine Block Porosity
2.0L EcoBoost Coolant Intrusion - Open-Deck Block Failure
1.6L EcoBoost Engine Overheating and Coolant Loss - Recall 14S11
EcoBoost Coolant Intrusion into Cylinders
Fuel System Issues and Stalling
1.6L EcoBoost Intake-Valve Carbon Buildup (Direct Injection)
Intake-Valve Carbon Buildup on Direct-Injected EcoBoost Engines Causing Rough Idle and Misfire
P0171/P0174 Lean Codes from Cracked PCV Elbow / Intake Vacuum Leak (Triton)
3.8L V6 Head Gasket Failure
2.0L SPI Head Gasket Failure
6.0L Powerstroke Head Bolt Failure and Head Gasket Blowout
3.0L Vulcan V6 Head Gasket Failure
3.8L V6 Head Gasket Failure
DPFE Sensor / EGR Failure Setting P0401 and Companion P0171/P0174 Lean Codes
Intake Manifold / PCV Vacuum Leak on 4.0L SOHC Causing P0171/P0174 Lean Codes and Rough Idle
3.0L Vulcan Lower Intake Manifold Gasket / Coolant Tube Leak
2.4L I4 Excessive Oil Consumption and Piston Ring Failure
LML Duramax EGR Cooler and EGR Valve Failure
Direct Injection Carbon Buildup on Intake Valves
Cracked Exhaust Manifold Bolts / Manifold Leak (5.3L/6.2L V8) Causing Cold-Start Tick
4.3L Central Port Injection (CPI) Spider Injector Failure
4.3L V6 Intake Manifold Gasket Leak
Fuel Pump Module Failure Causing No-Start or Stalling
4.3L V6 Intake Manifold Gasket Leak
5.7L Vortec Spider Injector Assembly Failure
Fuel Pump Module Failure Leading to No-Start or Intermittent Stalling
5.7L Vortec Intake Manifold Gasket and CPI Issues
1.5L Turbo Engine Oil Dilution
VCM Oil Consumption and Piston Ring Failure
VCM System Causes Excessive Oil Consumption and Misfires
V6 VCM Excessive Oil Consumption and Engine Vibration
1.5T Earth Dreams Direct Injection Carbon Buildup on Intake Valves
11th Gen Civic Oil Consumption and Honda Sensing Phantom Braking
11th Gen 2.0T Direct Injection Carbon Buildup and Idle Vibration
VCM System - Excessive Oil Consumption and Misfires
Engine Excessive Oil Consumption
VTEC Oil Consumption and Burning
Engine Oil Consumption (K24A High Mileage)
Idle and Stalling Problems
VCM System Oil Consumption and Engine Damage
EGR System Clogging (Lean Burn Engine)
Cracked cast-iron exhaust manifold near the oxygen sensor
Excessive Oil Consumption - 2.4L GDI Engine
Oil Dilution / Gasoline Contamination in Engine Oil
Excessive Oil Consumption - 3.8L Lambda V6
Intake Manifold Gasket Leak
Head Gasket Failure (Shared Excel Platform)
Head Gasket Failure (Mitsubishi G4DJ/G4EK)
P0171 — System Too Lean (Bank 1) from Vacuum Leak / Dirty MAF
P0171 — Bank 1 Lean from Intake Manifold Gasket Vacuum Leak / Stuck Purge Valve
Excessive Oil Consumption (2.4L Tigershark)
Pentastar V6 Oil Consumption
2.4L Tigershark Oil Pump Failure / Engine Stalling
2.4L Tigershark Excessive Oil Consumption
2.4L Engine Excessive Oil Consumption
3.7L V6 Exhaust Manifold Crack / Valve Cover Oil Leaks
Fuel system fault / stalling or no-start related to low-pressure fuel pump module
Fuel Injector Leak / Fuel Smell in Engine Bay (3.0L Hurricane)
P0171 — System Too Lean (Bank 1) from 3.6L Pentastar Intake Manifold Gasket / Vacuum Leak
Excessive Oil Consumption
Nu 2.0L GDI Engine Knocking and Oil Consumption
Premature Catalytic Converter Failure (2.4L GDI)
Piston Oil Ring Defect and Excessive Oil Consumption
Intake Valve Carbon Buildup (GDI Engines)
Piston Oil Ring Defect and Engine Damage
Fuel Injector Failure and Engine Stalling
Apex Seal Failure / Compression Loss
Carbon Buildup on Intake Valves (Skyactiv)
Excessive Engine Oil Consumption
Rough idle / stalling from idle air control valve and intake manifold gasket
Direct Injection Carbon Buildup on Intake Valves
Oil Separator / Crankcase Ventilation Valve Failure Causing Oil Consumption (N14/N18)
High-Pressure Fuel Pump (HPFP) Failure (N14/N18/B48 Turbo DI)
Excessive Oil Consumption (VQ35DE Engine)
VQ35DE Excessive Oil Consumption
Rear Main Seal and Valve Cover Oil Leaks
Twin Turbo Fuel System Degradation
Engine Oil Leaks (Multiple Locations)
Exhaust Manifold Stud Breakage and Manifold Leak Tick
VQ35DE Rev-Up Engine Oil Consumption
Vacuum Hose Deterioration Causing Boost and Idle Problems (Twin Turbo)
1.5L VC-Turbo Engine Oil Smell, Rough Running, and Check Engine Light from PCV / Crankcase Ventilation Faults
P0171 — System Too Lean (Bank 1) from Cracked Intake Air Duct or Leaking Intake Manifold Gasket
P0171 — System Too Lean (Bank 1) from Leaking Intake Manifold Gasket / Cracked Intake Boot
Bonneville 3800 V6 Lower Intake Manifold (LIM) Gasket Failure
Grand Am 3.4L V6 Upper/Lower Intake Gasket Failure
G8 Fuel-Tank-Module Issues + Brake Lamp Switch Recall
Montana 3.4L V6 Intake Gasket — Same as Grand Am
Grand Prix 3800 V6 Lower Intake Manifold (LIM) Gasket Failure
Air-Oil Separator (AOS) Failure
Air-Oil Separator (AOS) Diaphragm Failure
Air-Oil Separator (AOS) Failure
Air-Oil Separator (AOS) Failure Causing Oil Ingestion and Smoke
Head Gasket Failure
EJ253 Head Gasket Failure (External Leak)
EJ25 Head Gasket Failure
FB25 Engine Excessive Oil Consumption
Excessive Oil Consumption
Excessive Oil Consumption
FB20 Engine Excessive Oil Consumption
EJ25 Head Gasket Failure
Piston Ringland Failure
FB25 Engine Oil Consumption
Head Gasket Issues
Denso Low-Pressure In-Tank Fuel Pump Failure Causing Sudden Stalling
FA24F PCV Hose Oil/Fuel/Hot-Rubber Odor Under Hood (TSB 11-204-23)
2GR-FE V6 Excessive Oil Consumption
2AR-FE Engine Excessive Oil Consumption
2AZ-FE Engine Excessive Oil Consumption
EGR Valve and Intake Manifold Carbon Buildup
Water Pump Leak and Failure (2GR-FE)
1NZ-FXE Head Gasket Failure and EGR Cooler Issues
FA24 Engine Oil Consumption
3rd Generation 2ZR-FXE Excessive Oil Consumption
Low-Pressure Fuel Pump Failure and Engine Stall
G16E-GTS Head Gasket Seepage Under Hard Use
Intake Manifold Gasket Vacuum Leak Causing Cold-Start Rough Idle and Lean Codes
Ignition Coil and Intake/PCV Failure Causing Random Misfire (2.7L 1AR-FE / 2GR V6) — P0300
1GR-FE 4.0L V6 Cracked Exhaust Manifold Causing Ticking and Exhaust Leak
Fuel Pump Failure / No-Start from Defective Denso Pump Impeller
1ZZ-FE Engine Excessive Oil Consumption (GT)
Head Gasket Failure (Supercharged Models)
3.4L 5VZ-FE Head Gasket Failure
22R-E Head Gasket Failure
Head Gasket Failure
Direct Injection Carbon Buildup on Intake Valves
Head Gasket Failure (5E-FE)
Denso Low-Pressure Fuel Pump Failure Causing Engine Stalling (Recall 20V-012)
Denso Low-Pressure Fuel Pump Failure Causing Engine Stall (Recall 20V-682 / 20TA02)
1ZZ-FE Oil Consumption (MR2 Spyder)
Denso Low-Pressure Fuel Pump Failure and Stalling (Recall)
Dirty/Failed Mass Air Flow Sensor Causing P0171 Lean Code and Rough Idle
Direct Injection Carbon Buildup on Intake Valves
Valve Cover Gasket and PCV Valve Oil Leak
1.8T/2.0T EA888 Excessive Oil Consumption
Intake Valve Carbon Buildup
PCV Valve/Diaphragm Failure
PCV Valve/Diaphragm Failure
EA888 PCV / Crankcase Ventilation Failure Causing High Oil Consumption
CIS Fuel Injection System Issues
PCV Valve Diaphragm Failure
PCV Valve / Oil Separator Diaphragm Failure
EA888 PCV Valve / Oil Separator Diaphragm Failure
2.0 TSI/FSI Carbon Buildup on Intake Valves (Direct Injection)
PCV Breather System Failure
T5/T6 PCV Oil Trap System Failure and Oil Consumption
Excessive Oil Consumption
T5/T6 Engine Excessive Oil Consumption
2.5L T5 PCV Oil Trap/Breather Box Failure
PCV System and Oil Trap Clogging
PCV Oil Trap/Separator Failure
PCV System Flame Trap Clogging
LH-Jetronic Fuel Injection and Idle Issues
PCV System Clogging and Oil Leaks
PCV Oil Trap System Failure
PCV Breather Box and Oil Trap Failure
PCV / Oil Trap (Crankcase Ventilation) Failure on Inline-5 and Inline-6 Engines
FAQ
What does P0171 mean?
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.
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?
Repair costs for P0171 range from $20 to $15,000, depending on the vehicle and root cause.
Which vehicles are affected by P0171?
Au7o has documented P0171 across 187 vehicle models from 27 manufacturers: Audi, BMW, Buick, Chevrolet, Chrysler, Dodge, Ford, GMC, Honda, Hyundai, Jaguar, Jeep, Kia, MINI, Mazda, Mercedes-Benz, Mercury, Nissan, Opel, Pontiac, Porsche, RAM, Ram, Subaru, Toyota, Volkswagen, Volvo.
Sources (12)
- mediaClass Action Honda Hid Engine Oil Dilution Defect Newer CR-V - ClassAction
- media2017 Honda CR-V High Oil Level With Gas In Oil - CarComplaints
- mediaHonda Oil Dilution Lawsuit Includes Accord Civic and CR-V - CarComplaints
- ForumHead Gasket Failure in 2.2 liter models - Subaru Outback Forums
- mediaSubaru Head Gasket Problems Explained - All Wheel Drive Auto
- ForumEj25 sohc 2000 ob head gasket - Ultimate Subaru
- mediaSubaru Head Gasket Problems Crucial Years - Automotive Body Care
- mediaValero Law: Class-Action over FCAs Tigershark Oil Consumption Defect
- mediaMyCarVoice: Fiat Chrysler 2.4L Tigershark Engine Class Action Settlement Announced
- ForumJeep Renegade Forum: 2.4L Tigershark Class Action Lawsuit and Oil Consumption Issues
- mediaThe Lemon Firm: Jeep Cherokee 2.4L Tigershark Oil Consumption Causes Engine To Stall
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.