P0171 Code - Fuel Trim System Lean Bank 1
Quick Answer
The Engine Control Module (ECM) controls a Closed Loop air/fuel metering system to provide the best possible combination of drivability, fuel economy, and emission control. Common causes include Dirty or Restricted Air Filter, Dirty or Faulty Mass Air Flow (MAF) Sensor, Intake Air Leaks. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
- What it means
- P0171 indicates Fuel Trim System Lean Bank 1.
- Common causes
- Common causes include Dirty or Restricted Air Filter, Dirty or Faulty Mass Air Flow (MAF) Sensor, Intake Air Leaks.
- Severity
- High - diagnose this code as soon as possible.
- Can I drive?
- Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
Code P0171 Description
What are the Possible Causes of the DTC P0171?
- Dirty or Restricted Air Filter
- Dirty or Faulty Mass Air Flow (MAF) Sensor
- Intake Air Leaks
- Exhaust Gas Leaks
- Fuel Contamination
- Faulty or Clogged Fuel Injectors
- Faulty Front Heated Oxygen Sensor
- Ignition Misfiring
- Low Fuel Pressure
- Positive Crankcase Ventilation (PCV) Hose Leaks
How to Fix the DTC P0171?
Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.
Code Tech Notes
Click Here to Learn What is Bank 1 and Bank 2
User Submitted Video
What is the Cost to Diagnose the Code?
Labor: 1.0
To diagnose the P0171 code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.
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Information for Specific Makes
- P0171 Acura — Fuel System Too Lean
- P0171 Audi — System Too Lean Bank 1
- P0171 BMW — Mixture Control System Too Lean
- P0171 Buick — Fuel Trim System Lean Bank 1
- P0171 Cadillac — Fuel Trim System Lean Bank 1
- P0171 Chevrolet — Fuel Trim System Lean Bank 1
- P0171 Chrysler — Fuel System 1/1 Lean
- P0171 Dodge — Fuel System 1/1 Lean
- P0171 Ford — Fuel Injection System Too Lean Bank 1
- P0171 GMC — Fuel Trim System Lean Bank 1
- P0171 Honda — Fuel Injection System Too Lean Bank 1
- P0171 Hummer — Fuel Trim System Lean Bank 1
- P0171 Hyundai — System Too Lean Bank 1
- P0171 Infiniti — Fuel Injection System Too Lean Bank 1
- P0171 Isuzu — Fuel Trim System Lean Bank 1
- P0171 Jaguar — System Too Lean Bank 1
- P0171 Jeep — Fuel System 1/1 Lean
- P0171 KIA — Bank 1 System Too Lean
- P0171 Land Rover — System Too Lean Bank 1
- P0171 Lexus — Fuel Trim System Too Lean Bank 1
- P0171 Lincoln — Fuel Injection System Too Lean Bank 1
- P0171 Mazda — Lean Air/Fuel Ratio Bank 1
- P0171 Mercedes-Benz — System Too Lean Bank 1
- P0171 Mercury — Fuel Injection System Too Lean Bank 1
- P0171 MINI — Mixture Control System Too Lean
- P0171 Mitsubishi — System Too Lean Cylinders 1-4
- P0171 Nissan — Fuel Injection System Too Lean Bank 1
- P0171 Oldsmobile — Fuel Trim System Lean Bank 1
- P0171 Pontiac — Fuel Trim System Lean Bank 1
- P0171 Saab — System Too Lean Bank 1
- P0171 Saturn — Fuel Trim System Lean Bank 1
- P0171 Scion — Fuel Trim System Too Lean Bank 1
- P0171 Subaru — System Too Lean Bank 1
- P0171 Suzuki — System Too Lean Bank 1
- P0171 Toyota — Fuel Trim System Too Lean Bank 1
- P0171 Volkswagen — System Too Lean Bank 1
- P0171 Volvo — System Too Lean Bank 1
Frequently Asked Questions about P0171 Code
1. What does the OBDII code P0171 mean?
Code P0171 means that the oxygen sensor in bank 1 has detected too much oxygen in the exhaust relative to the fuel being injected into the engine, indicating a lean condition.
2. What are common symptoms of the P0171 code?
Symptoms can include a rough idle, hesitation or stumbling when accelerating, reduced fuel economy, and the check engine light being illuminated.
3. What could cause a P0171 code in a vehicle?
Causes can range from a vacuum leak, faulty mass airflow sensor, weak fuel pump, dirty fuel injectors, to an exhaust leak before the first oxygen sensor.
4. How can I fix the P0171 code?
Repairs might involve checking for and repairing any vacuum leaks, replacing the mass airflow sensor or oxygen sensor, cleaning or replacing fuel injectors, or ensuring proper fuel pressure from the fuel pump.
5. Is it safe to drive a car with a P0171 code?
While you can drive for a short distance, it's important to address the issue soon as it can lead to engine performance issues, higher emissions, and potentially more serious engine problems.
6. How does a mechanic diagnose the P0171 code?
A mechanic will typically start with a visual inspection for obvious issues like vacuum leaks or damaged components, then use a scan tool to check sensor data, and may perform a smoke test to detect any hard-to-see leaks.
7. Can a dirty air filter cause a P0171 code?
Yes, a dirty air filter can restrict air flow to the engine, contributing to a lean mixture and potentially triggering this code.
8. What does 'Bank 1' refer to in the P0171 code?
'Bank 1' refers to the side of the engine that contains the first cylinder. In V-configured engines, this is typically the bank of cylinders on one side of the engine block.
9. Is replacing the oxygen sensor always necessary to fix the P0171 code?
Not necessarily; it's important to diagnose other potential causes thoroughly, such as vacuum leaks or fuel delivery issues, before replacing the oxygen sensor.
Discuss the causes and fixes for P0171 OBDII Code
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Great site. The first suggestion fixed my problem on my 2004 mazda 6 3.0 liter v6. I had po300, po171, and po172. The car had rough idle. replaced a cracked intake manifold vacuum hose located by the firewall. Problem fixed. Car is running fantastic again. Thanks for sharing this information.
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What makes my 2004 strats keep thowing the code running lean on bank 1 and all replace a new O2 at the top so what is my promblem please help thank s
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hi there I have replaced my 2.0 FSI 2006 Passat ecu with Audi 2.0fsi ecu but now I don't have a code for a gear to set can some one please help me
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Start by checking for intake leaks. If no leaks are found, then clean or replace the Mass Air Flow (MAF) sensor and air filter.
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Hi, I have a 2014 Vauxhall Corsa 1.0 ecoflex I have the code P0171 Code - Fuel Trim System Lean Bank 1 was wondering if anyone had any suggestions to try to find the problem, I have been told to try replace purge valve first
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The purge valve can cause a lean condition by allowing excess air into the intake, which disrupts the air-fuel mixture. If the valve is stuck open, it can cause extra fuel vapors to enter the intake manifold, leading to a lean condition. However, it's not very common for a faulty purge valve to trigger the P0171 code. Instead, I suggest checking the following:
- Vacuum Leaks: A common cause of a lean condition is unmetered air entering the system. Check for vacuum leaks around the intake manifold, throttle body, and hoses.
- Mass Air Flow (MAF) Sensor: A dirty or faulty MAF sensor can cause incorrect air measurements, leading to a lean condition. Try cleaning the MAF sensor with a specialized cleaner or consider replacing it if cleaning doesn't resolve the issue.
- Exhaust Leaks: Leaks before or near the oxygen sensor can cause the sensor to read a lean mixture. Inspect for any exhaust leaks and repair them if necessary.
- Fuel System Issues: A weak fuel pump, clogged fuel filter, or dirty fuel injectors can lead to insufficient fuel delivery. Check the fuel pressure and inspect the fuel system components.
- Oxygen (O2) Sensor: A faulty upstream O2 sensor can give incorrect readings to the ECU, causing a lean condition. If the sensor is old, consider replacing it.
Steps to Try:
- Check for Vacuum Leaks: Inspect all vacuum hoses and connections for cracks, leaks, or disconnections. Spray carb cleaner around the intake area while the engine is running; if the idle changes, it could indicate a leak.
- Clean or Replace the MAF Sensor: If dirty, clean the MAF sensor using a MAF sensor cleaner. If cleaning doesn’t help, consider replacing it.
- Inspect and Test the Purge Valve: As mentioned, a faulty purge valve can disrupt the air-fuel ratio. If it’s sticking or malfunctioning, replacing it may help.
- Check the Fuel System: Ensure that the fuel pump is delivering the correct pressure and verify that the fuel filter and injectors are not clogged.
- Check the O2 Sensors: Test the upstream O2 sensor for functionality, and if it’s faulty, consider replacing it.
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