If the powertrain control module (PCM) determines that the air-to-fuel ratio is too lean, this will set a P0171 code. This indicates that the PCM thinks the engine is receiving too much air relative to fuel.
The PCM is always receiving signals from the oxygen sensors and shifting the amount of air and fuel to be added to the combustion chamber. This is done to provide balanced readings based on the sensors’ input.
In this problem, the range for fuel requirements preset by the factory has been crossed, and the motor needs less fuel, which is arguably the lowest permissible limit. Hence, the PCM will set the P0171 code.
The PCM subsequently requests more fuel through the fuel injectors to the combustion chamber of the engine. This procedure is known as fuel trimming. In this instance, where there is a P0171 code, it indicates that more fuel is necessary, and so this is deemed a positive fuel trim.
What Does the P0171 Code Mean?
The Code P0171 stands for “Fuel Trim System Too Lean (Bank 1)”.
Excessive increase in fuel resulting from adding to the air based on O2 sensor readings will trigger the fault code P0171, which will in turn light up the check engine light.
This code could also imply that the oxygen sensor is registering an excessive amount of oxygen or a significantly insufficient amount of fuel in the mixture.
Calling the fuel shortage a lean mixture means that, in simplistic terms, what a code P0171 means is that there is a running with too lean a mixture and thus the system is underperforming.
When NOx gases are emitted into the atmosphere as a byproduct of combustion while using leaner fuel mix vehicles, which are considered more environmentally damaging than vehicles running with rich fuel mixtures. Leaner vehicles also tend to misfire as hydrocarbons from unburnt fuel reach the catalytic converters.
Increased fuel consumption, damage to the vehicle’s exhaust system, and failure to meet emission standards are some of the potential side effects this could lead to.
To know more about rich and lean OBD codes, you can refer to our conversation regarding the air-fuel mixture. You may read our discussion about the ideal mixture and OBD codes if you wish to learn more about how the air-fuel mixture can trigger codes to be stored in a vehicle technically.
For now, move on to the next section to obtain the information faster and understand the potential issues behind the P0171 code.
When this code is set, oxygen sensors note low levels of oxygen present in the exhaust (lean condition); therefore, the module attempts to add fuel to the system more than it would normally do to achieve the balance in the air/fuel mixture.
- Rich Mixture = Too much fuel, not enough air
- Lean Mixture = Too much air, not enough fuel
Symptoms of this DTC
There are cases when you would notice that your check engine light comes on and your vehicle remains unchanged in the way it operates. The vehicle will show additional symptoms after it has been scanned for trouble codes and P0171 is found along with other codes.
“The engine is too much air inside the engine.” When your engine is on but you are not moving, the engine will likely provide you with this rough idle feature or cough sound.
As you drive, you may feel that your car struggles to gain power while trying to accelerate or when driving uphill. You might even feel some engine misfire.
If you do not observe any difference while driving your car with the P0171 error code and there is no change in the performance, then you might have a malfunctioning sensor. These components are often known to fail.
But even without other accompanying symptoms, it is important to check that the components around the sensor are functioning properly. It is critical to ensure that the sensor has not been damaged, as replacing expensive parts without reason would be frustrating.
Common causes of P0171 Code
The first place to start when a P0171 code is stored in the vehicle is the vacuum system. The vehicle’s vacuum lines can develop a small tear or crack, changing the normal distribution of airflow.
There are several sources for a leak that can trigger trouble code P0171, and these are said to be the engine intake, intake manifold gasket, PCV hoses, and vacuum hoses.
If none of the vacuum lines have any apparent cracks, it is then reasonable to conclude that the problem originates from the fuel system. There is not enough gasoline reaching the pump, which terminates the supply within a weak or failing fuel pump.
Provided that the vacuum system is leak-free, gas reaching the engine is adequate, and the code P0171 is still illuminated, it may be possible to identify the problem.
The sensor responsible could have an issue, or they could be failing; be it a dirty Oxygen sensor, mass airflow sensor, or air-fuel ratio sensor. Readings could also be affected if there is an exhaust leak.
Is Code P0171 Serious?
The check engine light indicates that something is wrong with the vehicle, and the specific reasoning behind the light should not be disregarded. The same can be said for P0171. In light of this code, the best course of action is to limit vehicle range if any travel is needed.
Operating a car in a lean condition can lead to serious problems because the fuel is insufficient for efficient functioning. In terms of vehicle performance, this can decrease the ability to accelerate with traffic or climb steeper roads. There is also a risk of overheating that can lead to damage.
Vehicles that have had their turbocharged boost modified are more likely to have undergone a P0171 code. The correlation between power and air is direct. However, to avoid issues, there needs to be a proper fuel supply for optimal air-to-fuel ratio.
At worst, a car using up fuel inefficiently, as is the case with a car showing error code P0171, can result in excessive spending on gas. It’s likely the driver will spend far more than what is necessary to operate the vehicle.
How to Diagnose Code P0171?
Make sure to conduct a thorough OBD-II scan on your car before you make assumptions about the underlying issue’s reason. You or a mechanic need to check for Code P0171, which will confirm this is the right diagnosis for your car’s problems and there are no other issues present while seeing a check engine light.
It is easy to think replacing some sensors will get the problem solved as quickly as possible, but a proper OBD-II scan will show the car issues occur pertaining right around Bank 1. It pays to have someone with a background in solving Code P0171 issues check on the matter.
To solve the problem, a thorough clean-up of the work area should be done to get access to the restricted region that needs work.
After identifying Code P0171, follow these steps in order until the source of the error message is found, and you should succeed in finding something of value.
- Examine the vacuum gauge to find leaks with the engine switched off.
- Use a fuel pressure measuring device to analyze fuel sensors and mass flow air sensors for the required value.
- Test oxygen sensors in the entire fuel system using the specified manufacturer’s procedures.
- After every other option has been exhausted, the issue is most likely with the power control module.
How Do I Fix the P0171 Code?
The error for the Bank 1 system operating too lean can be fixed using various methods. Some of these corrective actions may be sufficient to deactivate the check engine warning light:
- Fuel pump or filter replacement
- Change of the fuel pressure regulator
- Replacement of the control module
- Change of one or multiple fuel injectors
- Change of one or more oxygen sensors
- Change the mass air flow sensor
- Vacuum leak repair
Performing maintenance, including oil changes, tune-ups, and general routine servicing,g is one way to mitigate the P0171 code from reappearing.
Cost to Fix Code P0171
Keep in mind that these price may differ depending on the region, associated repair fees, and the vehicle’s brand and model.
- Vacuum/PCV Hose – The cost of replacing a vacuum or PCV hose is typically in the range of $90 to $190 for both parts and labor. Generally, the costs of the parts stay within $10 to $50 while labor costs vary from $80 to $140, depending on the shop where the vehicle is taken for servicing.
- Intake Manifold Gasket – An intake manifold gasket replacement may cost you anywhere between $100 and $500. The gasket, along with the bolts, is likely to cost $20 to $100, with labour expected to be in the range of $80 to $400, again depending on the specifics of your vehicle.
- Fuel Pump – Fuel pump replacement is among the more expensive services, with a price range of $300 to $800. A fuel pump, for instance, will typically incur a cost of $100 to $400, with labour cost being around $200 to $400.
- Fuel Injector – The cost of replacing a fuel injector may range from $130 to $800, depending upon your vehicle’s make and model. The portion itself, the injector, can cost $50 to $300, with labor costs expected to rise from $80 to $500.
- Fuel Filter – Replacing a fuel filter is a less expensive service that can cost anywhere from $90 to $190. The filter itself costs between $10 and $50, and the service charge for the replacement is expected to be between $80 and $140.
- Oxygen Sensor – The cost to have an auto shop replace an oxygen sensor ranges between $100 and $400. This price depends on the area and the service shop. The average cost of an oxygen sensor is between $20 and $200, and the charges for replacing it are normally around $80 to $200.
- MAF Sensor – The price of replacing the Mass Air Flow (MAF) sensor ranges from $200 to $500. The automobile service centre usually charges between 100and100and300 for the MAF sensor itself, in addition to about $100 to $200 for labour.
- Air/Fuel Ratio Sensor – The expected price for replacing the air/fuel ratio sensor is around $130 to $500. The sensor piece itself is likely to be priced between $50 and $300. Furthermore, costs for service labour are between $80 and $200.
Why Does a P0171 Code and Running “Too Lean” Matter?
Light trucks and cars that run on “lean” are considered to be excessively polluting vehicles. An alarming number of those suffering from respiratory problems like asthma is the direct result of “lean burning” vehicles.
Both lean and rich running vehicles have their problems, however, a lean running vehicle has the additional issue of misfires.
Such misfires release uncontrolled hydrocarbons (HCs) into the environment during combustion, which subsequently results in the destruction of the catalytic converter, among other things. The byproduct is hazardous fumes that pollute the air and are harmful to humans, burning their eyes in the process.
On the bright side, if we consider an engine that is running rich but does not misfire, it will either emit “odorless” carbon monoxide (CO) or, as some might describe, a “rotten egg” scent due to sulfur dioxide released from the catalytic converter.
A P0171 code does not stem from malfunctioning oxygen sensors. It is important to note that there is always a series of checks and tests conducted to ascertain the accuracy of readings from the oxygen sensors before ascertaining a P0171 code.
As mentioned before during the readiness tests for the oxygen sensors, should these not set any codes, it follows that the computer will tend to Fuel Trim adjustment. Once ascertaining the a: F ratio is too lean, the code P0171 will then set.
What if There Is No Vacuum Leak, and Codes P0171 code is Set?
An “underreporting” Mass Air Flow Sensor can be a common cause of a code P0171. Essentially, this means that the Air Flow Sensor is telling the computer that much less air is entering the engine than is.
Since the oxygen sensors are telling the computer that more fuel is needed, this confuses the computer because the Mass Air Flow Sensor is still saying there is too little air and the Oxygen Sensor is reporting that the mixture is still too lean.
The computer tried to compensate, but since resolution is impossible, it sets the code. It is important to restate that the Oxygen Sensors are accurate—the fuel mixture is too lean.
In this case, the Air Flow Meter or Sensor is inaccurately reporting the real amount of air entering the engine.