P0171 code definition
System Too Lean (Bank 1)
What the P0171 code means
The P0171 code means that, on the first bank of the engine, the fuel system is running weak or a vacuum leak exists near this side of the engine. A lean condition occurs when the engine either receives too little fuel or too much air.
What are the causes of the P0171 code?
Causes of the P0171 code may include:
- A faulty fuel pressure regulator
- A weak fuel pump
- A clogged fuel filter
- A faulty powertrain control module
- A vacuum leak
- Faulty injector(s)
- Faulty oxygen sensor(s)
- A faulty mass air flow sensor
What are the symptoms of the P0171 code?
Symptoms of the P0171 code may include:
- Loss of power
- Check Engine Light
- Hesitation or stumble from the engine
- Engine may be difficult to start
- Engine may die
- Catalytic converter damage may result if this code is stored for a long period of time
How does a mechanic diagnose the P0171 code?
Assuming that no other trouble codes exist, a mechanic may diagnose the P0171 code by checking the engine for vacuum leaks with a vacuum gauge and checking the fuel pressure with a fuel pressure gauge.
In order to maintain a proper air/fuel ratio, the vacuum and fuel pressure of the engine must be within the manufacturer’s specifications. The cause of this trouble code will likely be discovered during one of these two tests. If the cause of this issue is still not found after the mechanic has performed these two tests, the problem likely lies with a sensor.
The mechanic would then run tests on the mass airflow sensor and the oxygen sensors using the manufacturer’s procedure. If all of these tests have been performed and no issues are found, the problem is likely the powertrain control module.
Common mistakes when diagnosing the P0171 code
A common mistake that could be made when diagnosing the P0171 code would be not looking for any technical service bulletins for your specific car model that may be related to this issue.
Although every trouble code will not have a technical service bulletin associated with it, it is always wise to check as they can save you a world of time and effort.
How serious is the P0171 code?
The P0171 code is a serious issue. If a vehicle has this code stored in its powertrain control module, the engine of that vehicle simply will not run well. If the engine does not maintain proper air/fuel ratio, there will be a major waste of fuel and a lack of power while driving. It is a good idea to have this code diagnosed and repaired as soon as possible to have your vehicle running smoothly.
What repairs can fix the P0171 code?
- Replacing the fuel pump
- Replacing the fuel filter
- Replacing the fuel pressure regulator
- Replacing the powertrain control module
- Replacing one or more injectors
- Replacing one or more oxygen sensors
- Replacing the mass air flow sensor
- Repairing a vacuum leak
Additional comments regarding the P0171 code
It is unwise to drive a vehicle with this trouble code stored for a long period of time. If an engine runs improperly for a long period of time, further damage may result that could end up being much more costly to the owner of the vehicle.
Need help with a P0171 code?
YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.
This article originally appeared on YourMechanic.com as P0171 OBD-II Trouble Code: System Too Lean (Bank 1) and was authored by Andrew Quinn.