An OBDII scan tool will give the error message “P0171 “Bank 1 System Too Lean.”
What Is a P0171 Error Code?
Bank-1 is the side of the engine with the number one cylinder.
A 4-cylinder will only have 1-Bank, while a V6 or V8 engine will have 2-Banks.
Find the side of the engine with the number-1 spark plug, and that will be the side having the issue.
The term Lean means the cylinder is receiving too much oxygen or too little fuel creating a bad lean fuel mixture.
The air-fuel mixture needs to be correct when it goes into a cylinder, or it will not burn correctly.
What Causes a P0171 Code?
- Mass Air Flow Sensor
- Vacuum Leak
- Bad Oxygen Sensor
- Bad Fuel Pressure Regulator
- A Weak or Failing Fuel Pump
- Fuel Filter
- Bad Injector
Several things can cause a P0171, with the most common failures being the Mass Air Flow Sensor or Vacuum Leak.
Vehicle Symptoms P0171 Code
- Loss of Power
- Engine Hesitation
- Engine Difficult to Start
- Engine Dies Easily
- Black Smoke From The Tailpipe
P0171 Error Code Fixes
- Replace or Clean Mass Air Flow Sensor
- Find and Fix any Vacuum Leak
- Replace the Oxygen Sensor
- Replace Injector
- Replace Fuel filter
- Replace Fuel Pump
- Replace Fuel Pressure Regulator
Troubleshooting a P0171 OBDII Error Code
There are several components that must work together to get the right air and fuel pressure mix.
A vehicle computer uses the mass airflow sensor to adjust the air mix into the engine.
For this reason, the mass airflow sensor is commonly cleaned or replaced to fix a P0171 error code.
A vacuum leak can cause the mass airflow sensor to get a bad reading.
The first step would be to clean the mass airflow sensor to see if the problem goes away or the vehicle runs better.
Next, look for a vacuum leak using one of the many vacuum troubleshooting techniques.
Once a vacuum leak or mass airflow sensor is ruled out next step is to look at the fuel pressure.
A weak or failing fuel pump can cause the pressure to be off, messing up the mixture.
A clogged-up fuel filter or pressure regulator can also cause this problem.
The fuel injector may also be failing, causing a bad mixture to go into the cylinder.
A bad oxygen sensor can also cause an issue.
Modern cars and trucks have two oxygen sensors on each side of an engine called upstream and downstream.
OBDII scan tool’s live data can help greatly to see if an oxygen sensor is having an issue.
Have you had a vehicle with a P0171 OBDII error code? Let us know your thoughts below.