P0171: System Too Lean (Bank 1)
190 vehicles · 23 makes
P0171 is an OBD-II diagnostic trouble code meaning “System Too Lean (Bank 1).” The engine is running lean on Bank 1 — too much air or not enough fuel. One of the most common OBD-II codes across all makes. This code appears across 190 vehicle models from 23 manufacturers.
Common Causes
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 (190)
Excessive Oil Consumption
Intake Valve Carbon Buildup
PCV Valve/Breather System Failure
PCV Valve Diaphragm Failure and Oil Consumption
EGR Valve/Cooler Failure
Severe Carbon Buildup on Intake Valves (4.0T V8)
Direct Injection Carbon Buildup (Intake Valves)
Severe Carbon Buildup on Intake Valves (Direct Injection Engines)
Water Pump and Thermostat Housing Coolant Leaks
PCV Valve (Crankcase Vent Valve) Failure (3.0T)
PCV Valve Failure (Rough Idle and Oil Consumption)
Severe Carbon Buildup on Intake Valves (Direct Injection)
Carbon Buildup on Intake Valves (Direct Injection)
Direct Injection Carbon Buildup on Intake Valves
Severe Carbon Buildup Causing Valve Damage (3.0T TFSI)
Excessive Oil Consumption (2.0 TFSI Engine)
Severe Carbon Buildup on Intake Valves (Direct Injection)
Water Pump Failure (60k Mile Lifespan)
Severe Carbon Buildup on Intake Valves (3.0T)
Severe Carbon Buildup on Intake Valves
Severe Carbon Buildup on Intake Valves (2.5T 5-Cylinder)
Turbocharger Oil Strainer Failure (4.0T V8) - CRITICAL
Carbon Buildup on Intake Valves (2.9T Twin-Turbo V6)
Electronic Water Pump Failure (2.0T)
Water Pump and Thermostat Failure
Valve Cover/Gasket Oil Leak
Intake Valve Carbon Buildup
G80 S58 Engine Carbon Buildup on Intake Valves
Valve Cover Gasket Leak and PCV Failure
Fuel Injector Failure - 428i/430i/435i/440i F32/F33/F36
N63 Valvetronic Motor Failure - F01/F02 750i/750Li
Electric Water Pump Failure - E85 (N52) & E89 Z4
Valve Stem Seal Failure - Excessive Oil Consumption (E53 V8)
S55 High-Pressure Fuel Injector Failure - F82/F83 M4
Electric Water Pump Failure (N52, N20 Engines)
B58 Coolant System Failures (xDrive40i)
N63TU3 Oil Consumption & Valve Stem Seal Degradation (xDrive50i/M50i/M60i)
CCV/Oil Separator Failure Causing Vacuum Leaks, Oil Consumption, and Cold-Weather Hydrolock Risk
Electric Water Pump Failure (All Engines)
Electric Water Pump Failure (N52, N55, N63 Engines)
Carbon Buildup on Intake Valves (Direct Injection Engines)
Electric Water Pump Failure
N62 Valve Stem Seal Failure (Heavy Oil Consumption & Blue Smoke)
Electric Water Pump Failure (All Engines)
Electric Water Pump Failure (All 1 Series E82/E88)
Valve Cover & PCV System Failure (All 1 Series E82/E88)
Carbon Buildup on Intake Valves (Direct Injection Engines)
MAF Sensor Degradation Causing Lean Codes, Hesitation, and Reduced Power
N63 Valve Stem Seal / Oil Consumption (xDrive50i)
SMG III Hydraulic Pump Failure - E60 M5
S63/S63TU Valve Stem Seal Failure & Oil Consumption
Northstar 4.6L V8 Head Bolt/Head Gasket Failure
Northstar V8 Excessive Oil Consumption
Northstar 4.6L V8 Head Bolt/Head Gasket Failure
Northstar 4.6L V8 Head Bolt/Head Gasket Failure
4.6L Northstar V8 Head Gasket Failure (1993)
Northstar 4.6L V8 Head Bolt/Head Gasket Failure
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
3.1L/3.4L V6 Intake Manifold Gasket Leak (Dex-Cool)
PCV Valve Cover Failure and Oil Leak (1.4T)
In-Tank Fuel Pump Failure
4.3L V6 Intake Manifold Gasket Leak
3.4L V6 Intake Manifold Gasket Leak
2.2L/2.4L Head Gasket Failure
Excessive Oil Consumption (2.5L Ecotec LCV/LKW)
4.3L V6 Intake Manifold Gasket Leak
4.3L Vortec Central Sequential Fuel Injection (CSFI) Failure
Intake Manifold Gasket Leak (3.4L/3.8L V6)
4.3L V6 Intake Manifold Gasket Leak
Central Port Injection Fuel Leak Under Intake
5.7L Vortec Spider Injector Assembly Failure (CPI)
3.8L V6 Intake Manifold Gasket and Coolant Elbow Leak
1.8L 1ZZ-FE Oil Consumption Due to Piston Ring Design
1.2L/1.3L Turbo Engine Oil Consumption
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
2.5L V6 Head Gasket Failure
5.9L Magnum Plenum Gasket Failure
Cooling System Failures (3.3L/3.8L V6)
2.4L MultiAir Excessive Oil Consumption
2.4L DOHC Head Gasket Failure
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
Head Gasket Failure
2.4L Electronic Throttle Body Failure
5.2L/5.9L Engine Idle Surge and Hunting
2.2L/2.5L Head Gasket Failure
Gen 1 V10 Head Gasket Failure
Plenum Gasket Failure (5.2L/5.9L V8)
Intake Manifold Gasket Leak (3.9L V6 and 4.7L V8)
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
3.8L V6 Head Gasket Failure
3.0L Vulcan V6 Head Gasket Failure
3.8L V6 Head Gasket Failure
1.5L EcoBoost Oil Dilution From Short Trip Driving
2.0L SPI Head Gasket Failure
6.0L Powerstroke Head Bolt Failure and Head Gasket Blowout
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
4.3L V6 Intake Manifold Gasket Leak
5.7L Vortec Spider Injector Assembly Failure
Fuel Pump Module Failure Causing No-Start or Stalling
5.7L Vortec Intake Manifold Gasket and CPI Issues
4.3L V6 Intake Manifold Gasket Leak
Fuel Pump Module Failure Leading to No-Start or Intermittent Stalling
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)
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)
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
Excessive Oil Consumption
Nu 2.0L GDI Engine Knocking and Oil Consumption
Premature Catalytic Converter Failure (2.4L GDI)
Intake Valve Carbon Buildup (GDI Engines)
Piston Oil Ring Defect and Excessive Oil Consumption
Piston Oil Ring Defect and Engine Damage
Fuel Injector Failure and Engine Stalling
Head Gasket Failure (Mazda B-Series Engine)
Apex Seal Failure / Compression Loss
Carbon Buildup on Direct Injection Intake Valves
Carbon Buildup on Intake Valves (Skyactiv)
Excessive Engine Oil Consumption
Excessive Oil Consumption (VQ35DE Engine)
VQ35DE Excessive Oil Consumption
Twin Turbo Fuel System Degradation
Vacuum Hose Deterioration Causing Boost and Idle Problems (Twin Turbo)
Exhaust Manifold Stud Breakage and Manifold Leak Tick
Engine Oil Leaks (Multiple Locations)
Rear Main Seal and Valve Cover Oil Leaks
VQ35DE Rev-Up Engine Oil Consumption
1.5L VC-Turbo Engine Oil Smell, Rough Running, and Check Engine Light from PCV / Crankcase Ventilation Faults
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
Piston Ringland Failure
EJ25 Head Gasket Failure
FB25 Engine Oil Consumption
Head Gasket Issues
Head Gasket Failure (EA82 Engine)
FB20 Excessive Oil Consumption
2GR-FE V6 Excessive Oil Consumption
2AR-FE Engine Excessive Oil Consumption
EGR Valve and Intake Manifold Carbon Buildup
2AZ-FE Engine Excessive Oil Consumption
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
Head Gasket Failure (Supercharged Models)
1ZZ-FE Engine Excessive Oil Consumption (GT)
Fuel Pump Failure / No-Start from Defective Denso Pump Impeller
3.4L 5VZ-FE Head Gasket Failure
22R-E Head Gasket Failure
1ZZ-FE Oil Consumption (MR2 Spyder)
Head Gasket Failure
Direct Injection Carbon Buildup on Intake Valves
Head Gasket Failure (5E-FE)
Head Gasket Failure and Coolant Consumption (1NZ-FXE)
Intake Manifold Gasket Vacuum Leak Causing Cold-Start Rough Idle and Lean Codes
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
PCV Valve/Diaphragm Failure
CIS Fuel Injection System Issues
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 Flame Trap Clogging
PCV System Clogging and Oil Leaks
PCV Breather Box and Oil Trap Failure
PCV Oil Trap/Separator Failure
PCV System and Oil Trap Clogging
LH-Jetronic Fuel Injection and Idle Issues
PCV Oil Trap System Failure
FAQ
What does P0171 mean?
P0171 stands for "System Too Lean (Bank 1)." The engine is running lean on Bank 1 — too much air or not enough fuel. One of the most common OBD-II codes across all makes.
What are the most common causes of P0171?
The most common causes of P0171 are: Vacuum leak (intake gasket, hoses, PCV), Dirty or faulty MAF sensor, Weak fuel pump, Clogged fuel injector, Exhaust leak before O2 sensor. The specific cause varies by vehicle.
How much does it cost to fix P0171?
Repair costs vary widely depending on the root cause and vehicle.
Which vehicles are affected by P0171?
Au7o has documented P0171 across 190 vehicle models from 23 manufacturers: Audi, BMW, Cadillac, Chevrolet, Chrysler, Dodge, Ford, GMC, Honda, Hyundai, Jaguar, Jeep, Kia, MINI, Mazda, Mercedes-Benz, Nissan, Porsche, RAM, Subaru, Toyota, Volkswagen, Volvo.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.