The ECU needs to send an optimum mixture of air-fuel for optimized engine performance. However, certain conditions can impact this air-fuel mixture, resulting in a poor engine state.
P0171 is an intermediate engine fault code indicating that the system is lean near engine bank 1.
The main symptoms of this fault code include rough engine start, misfired cylinders, loss of power and rotten fuel smell from the exhaust.
There are many reasons of P0171 DTC including faulty fuel pressure regulator, faulty fuel injector, faulty MAF/oxygen sensors, vacuum leakage and clogged catalytic convertor.
The common solutions include resetting the DTC, changing the clogged filters, changing the MAF sensors, and changing the faulty fuel regulators, and injectors.
The lowest cost for resolution of this issue is around $35 to replace the filters and highest cost is around $2500 to replace the catalytic converter.
Introduction
The MAF sensor sends information to the ECU regarding the air entering the intake that helps it to decide the fuel injection for combustion. However, over the time, components such as MAF sensor, catalytic converters, air filter, air intake pipes, etc. get faulty resulting in the vacuum leaks or low air entering the engine (1).
When the ECU detects such malfunctioning, it illuminates a check engine light on the vehicle’s dashboard to aware the driver. The driver/technician can further connect a hand-code reader to further analyze the DTC and its main causes.
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This article is covering the major causes, symptoms, and solutions of P0171 DTC.
How to Read P0171 DTC
The following table has read every character of P0171 DTC (2):
Number of Character
Specific Character
What does it Signify
First
P
The problem lies within the powertrain part of the vehicle. This means that the engine, transmission, or fuel system can malfunction.
Second
0
This means that the code is standardized, so the SAE manual can be used further to interpret the code instead of the instruction manual.
Third
1
This number illustrates that the problem lies within the vehicle’s fuel or air metering system.
Fourth and Fifth
71
The specific fault index is 71 indicating that the system near engine bank 1 is lean.
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P0171 means that the problem lies within the powertrain and the code is SAE standardized. Further, the fuel or air metering system is faulty and the problem lies near the engine bank (1).
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Causes of P0171
Faulty Fuel Pressure Regulator
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A fuel pressure regulator functions to maintain the fuel pressure within the fuel injection system. If the system is requiring more fuel pressure, the regulator allows more fuel to enter into the engine and vice versa.
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There are certain signs that a fuel pressure regulator has gone faulty including the misfiring engine, leakage of the fuel and black smoke coming out of the car’s exhaust. A faulty fuel pressure regulator can either result in fuel-lean or rich conditions. High fuel pressure will result in rich running condition. Similarly, low fuel pressure will result in lean condition, where the amount of air in the engine will be too high as compared to the fuel (5). This can cause internal engine component failure if the issue is not resolved for a long time.
Faulty Fuel Injectors
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Another cause of P0171 is faulty injector. Fuel injectors function to deliver the right volume of fuel to the combustion chamber.
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It further ensures that the right amount of fuel is injected at the right time. However, faulty fuel injectors can send the wrong volume of fuel to the combustion chamber that can impact the engine’s performance. Usually, clogged fuel injectors send the wrong volume of fuel to the combustion chamber making the air-fuel mixture too lean (5). This will result in P0171 DTC.
Vacuum Leakage
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The major cause of engine code P0171 is vacuum leakage. Vacuum leakage is defined as a certain amount of air has entered the engine. Thus the air to the fuel ratio in the engine is disturbed and as a result, the performance of the engine is impacted.
Due to the excessive amount of air, the combustion process in the engine is affected. Because of the vacuum, the piston is moved downwards and the air is entered into the cylinders through the valve. The vacuum leakage makes the engine weak (1). The reading on the tachometer in the vehicle kept on fluctuating between 300 to 400 rpm. Also, the vehicle starts stalling and it becomes difficult to drive. The stalling occurs due to fluctuating fuel-to-air ratio and accidents can take place. Also, the misfire takes place in the cylinders due to the vacuum leakage. Thus, the engine code is illuminated to show that there is a vacuum leakage in the engine and if not treated, severe damage can occur.
Faulty Oxygen Sensor
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The other major cause of engine code P0171 is the faulty oxygen sensor. The role of oxygen sensor plays an important role in the vehicle system and it helps in controlling the exhaust particles of fuels.
The damaged oxygen sensor is the reason for the large production of nitrous and carbon oxides. Due to the damaged oxygen sensors, the engine will start consuming more amount of fuel and the efficiency of the engine becomes poor due to the unbalanced oxygen-to-fuel ratio (4). Also, there are chances that the vehicle will fail the emission test so there are chances that rotten egg-like smells are observed due to the sulfide deposition in the engine. This will release the black smoke from the exhaust and also the rough and noisy sounds will be observed from the engine. Thus, due to the following issues, the P0171 is indicated as a warning signal.
Clogged Catalytic Convertor and Faulty MAF Sensor
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The engine code P0171 is also indicated due to the clogged catalytic converter and defective mass air flow sensor. Both of these components are the major parts of the engine system.
A mass airflow sensor is used to determine the amount of air entering the engine. The defective mass airflow sensor will not detect the exact amount of air entering the sensors, and as a result, the engine will behave abnormally. This illuminates the engine code P0171 indicating the error with the airflow sensor (2). Other than it, the other reason for this code is the clogged catalytic converter. The catalytic converter may become clogged due to dirt, debris and the deposition of fuel. Thus, the process of burning the fuel in the catalytic converter is slowed down and it can cause serious damage to the engine.
Symptoms of P0171 DTC
Engine Cylinder Misfire/Rough Idle Start
The major symptom of the engine P0171 is the rough and idle engine. The engine becomes weak and makes noises due to various issues such as the disturbed air-to-fuel ratio in the engine.
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The vehicle fails to travel long distances with speed and there are fluctuations in speeds. The constant change in the speed in seconds can cause an accident. Also, the car experiences shakiness and vibrations. Due to the rough performance of the engine, the parts of the engine become rusted due to lack of lubrication and loud noises are heard from the engine (1). These symptoms are indicating that the car is suffering from fuel or oxygen issues. Either the amount of oxygen in the engine is too much or there is less amount of fuel in the engine.
Due to the engine code p0171, the misfire can be observed in the cylinders. This happens when the engine fails to produce the required amount of power and also, and it can occur due to a faulty oxygen sensor.
Rotten Exhaust Smell/Loss of Engine Power
The other major symptom due to engine code P0171 is the loss of power in the engine. This issue in the engine usually takes place when any part of the engine is clogged. So this issue indicates that the catalytic converter is not performing properly due to the dirt and debris inside it.
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When the catalytic converter is blocked due to the fuel deposition, the engine is unable to generate the required amount of power and as a result, the vehicle moves slowly. Other than it, due to the deposition of fuel, the combustion process is affected and nitrous and carbon oxides are not released in air (2). Thus, the rotten egg smell is observed and black coloured smoke is released from the exhaust system. When the engine light is indicated with the above mentioned symptoms, this indicates that the light is appearing due to engine code P0171.
Solution of P0171 DTC
Following are a few common solutions of P0171 DTC:
Reset the DTC and Test Drive
Like every other DTC, the common solution to this DTC is to reset the DTC using the hand-code reader. OBDII module can be situation in the car using the instruction manual and a hand-code reader can be used to reset the warning light and DTC (3). After resetting the DTC, test drive the vehicle for a few miles to check if the warning light illuminates again. If the check engine light illuminates again, then try finding the actual cause of this DTC.
Change the Clogged Air Filters
Another cause of this DTC is clogged air filter. A clogged air filter restricts the flow of air to the engine that will impact the air-fuel mixture making the mixture rich. So, the common solution to this issue is to check the air filters and replace them if they are clogged. The air filters are usually behind the glove box in normal vehicle models. However, in some advanced vehicle models, the air filter’s position can change and can be detected using the instruction manual. It is also recommended that the drivers change the air filters regularly to alleviate any complexities.
Change the faulty MAF Sensor
As discussed above that the faulty MAF sensor can also cause the air-fuel mixture to become lean or rich resulting in this DTC. In some cases, a faulty MAF sensor can send wrong information to the ECU that will result in wrong decision. So, check the MAF sensor that is located inside the intake (4). If the sensor is dirty, try cleaning it with soapy solution and take a test drive. If the issue persists, then it is recommended to replace the faulty MAF sensor.
Change the Fuel Pressure Regulator/Fuel Injector
If the fuel pressure regulator or fuel injector is faulty, it is recommended that you take the car to a professional service center. A professional will run various tests including the fuel pressure gauge. Further, a professional mechanic will have tools to inspect the air-fuel mixture, vacuum, and fuel pressure. Air-fuel mixture, vacuum and fuel pressure should lie within the manufacturer’s specifications, else the engine performance will be compromised.
Common Cost to Resolve the DTC
Following table illustrates the common cost to resolve the DTC:
Common Issues
Critical Level
Cost Required to Resolve the Issue
Dirty/Obstructed Mass Air Flow Sensor
Intermediate: Long-term driving with this issue can cause internal engine component failure
$100-200 to replace the faulty MAF sensor
Faulty Fuel Pressure Regulator
High: Wrong fuel pressure will impact the engine performance and can cause internal component damage
$250-550 to replace the faulty fuel pressure regulator
Vacuum Leak
Low: You can drive for intermediate distances with this issue
$20-50 to replace the damaged intake pipes and hoses
Clogged Air Filter
High: Driving along with a clogged air filter can damage the internal engine components
$15-25 to replace the clogged air filter
High: A failed catalytic converter will fail the emission test
High: A failed catalytic converter will fail the emission test
$900-2500 to replace the clogged catalytic converter
Faulty Fuel Injectors
High: Faulty fuel injectors can result in engine failure at a later stage
$240-350 to replace the faulty fuel injectors
Conclusion
To conclude, it can be said that P0171 is an intermediate DTC that indicates a lean mixture in engine bank 1. Therefore, it can cause the engine to misfire, resulting in low power and damage to the catalytic convertor in a longer run. The main causes of this DTC include faulty fuel pressure regulator, faulty fuel injectors, faulty oxygen sensors, vacuum leakage and faulty MAF sensors. So, if you are experiencing a low engine power, compromised fuel average and a check engine light, there is a chance that the DTC is P0171.
Yes, clogged fuel injectors will restrict the passage of fuel into the cylinders. Hence, the air-fuel mixture will be air enriched and the fuel will be less causing a lean condition. This can also illuminate the check engine light or P0171 DTC.
You should always test drive the vehicle after resetting the DTC. It is both in case of resetting the DTC before and after the component repair. It is because a test drive will give you an idea about the changes in the driving conditions of the car. Further, a test drive will also allow you to check if the problem arises again so you can resolve the issue at the earliest.
When the O2 sensor is faulty, it will send a signal to add too much fuel to the cylinder that can impact the engine performance. And when ECU detects that the ECM is adding too much fuel on the basis of the information sent by the O2 sensor, then it will illuminate the check engine light. The DTC can be P0171 or from P0100 family depending upon the issue.
