What is P0174 DTC? Common Symptoms, Causes, and Solution
A rough engine is mostly a sign that the air-fuel supply to the engine is limited or the mixture has become lean. However, suppose you are aware of OBDII and car warning lights. In that case, you can detect the exact location of the lean condition.
The following are the key takeaways from this article:
P0174 is an intermediate/severe DTC indicating a lean condition at engine bank 2.
The common symptoms of this DTC include reduced fuel average, misfiring engine, and check engine light.
The common causes of DTC P0174 include a faulty oxygen sensor, faulty MAF sensor, and faulty fuel pump.
Common solutions include replacing the MAF sensor, the oxygen sensor, the clogged air filter, replacing of fuel pump components.
The cost required to resolve this issue can range between $15 (in case of vacuum leakage) to $1500 (in case of fuel pump replacement).
Introduction
The oxygen sensor collects information about the air entering the cylinder and sends this information to the ECU. As a result, the ECU injects the right fuel into the engine’s cylinder for optimum performance (1). The ideal air-fuel ratio is 14.7:1, and the PCM can adjust this ratio by adding more fuel or taking away fuel to keep the engine running efficiently (3). The lean condition occurs when the oxygen sensor indicates PCM about too much air in the exhaust. PCM compensates for this by adding more fuel to bring the air-fuel ratio to the optimal value. But when PCM has reached the limit of injecting the fuel, it will detect a lean condition on the bank two oxygen sensor.
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An engine warning light will illuminate the vehicle’s dashboard, and DTC P0174 will be shown on the hand-code reader. P0174 is a severe intensity engine fault code indicating that the upstream oxygen sensor in engine bank two indicates a lean condition.
This article will further analyze this DTC’s causes, symptoms, and solutions.
How to Read P0174 DTC
The following table has read every character of P0174 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
74
The specific fault index is 71, indicating that the system near engine bank 2 is lean.
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P0174 means that the problem lies within the powertrain, and the code is SAE standardized. Further, the fuel or air metering system is faulty, and engine bank two reports lean air-fuel mixture condition.
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Causes of P0174 DTC
Following are a few common causes of P0174 DTC:
Defected Fuel Pump
A common cause of this DTC can be defected fuel pump. The defect in the fuel pump can be the restricted fuel filter that becomes clogged, making it difficult to push the fuel. Further, the fuel tank’s dirt and debris can also defect the fuel pump.
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It mostly happens when a driver replaces the fuel pump but needs to clean the fuel tank. The dirt particles at the bottom of the fuel tank can damage the fuel pump. Finally, wear and tear and water contamination can also defect the fuel pump (2). The tank can wear over time and can contaminate the fuel pump. A defective fuel pump will be unable to provide the optimum fuel to the engine cylinder causing the lean condition in the engine bank 2. Hence, the oxygen sensor will report greater oxygen in the exhaust gas resulting in this DTC.
Faulty MAF Sensor
The major cause of the engine code P0174 is the faulty mass air flow sensor. Mass airflow sensor plays an important role and is responsible for detecting the total amount of air entering the engine.
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The max air flow sensor can get defective due to various reasons. The engine’s performance is impacted as a reaction, and the engine light is turned on (4). When the mass air flow sensor is defective, the wrong amount of air in the engine will be detected. As a result, a large amount of fuel will enter the combustion chamber. A large amount of fuel will be burnt, and black-colored smoke will be released from the exhaust system.
Also, due to the increased combustion process, the layers of the oxides and nitrides will be deposited in the cylinder, and a rotten egg smell will also be released (3). Also, due to the dirt in the mass airflow sensor, the air-to-fuel ratio will be disturbed, making it difficult to start the car. This happens because the spark is required to turn on the engine, but an increased amount of air will become the hurdle to starting the car.
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Also, the car will fail to accelerate at high speed. Thus, due to a faulty mass airflow sensor performance of the engine becomes poor, and code P0174 is turned on.
Defected Oxygen Sensor
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The other major cause of the engine code P0174 is the poor oxygen sensor. The performance of the oxygen sensor can get poor for various reasons. One of the major reasons is the poor electrical connectivity o this sensor.
The purpose of the oxygen sensor in the engine is to calculate the amount of oxygen in the gasses that leaves the engine system. The sensors send the information to the electronic control unit of the engine. Then it helps predict the engine’s air-to-fuel ratio (5). However, due to the faulty oxygen sensor, the wrong amount of air-to-fuel ratio will be provided to the ECU system, which results in the engine’s poor performance. Also, the oxygen sensor gets impacted due to contamination by rich fuel, and a large amount of coolant will evaporate from the engine (2). This will damage the head gasket of the engine, and it will be impacted badly.
Vacuum Leakage
Also, the engine code P0174 is indicated because of the weak fuel pump. The fuel pump may become weak due to the leakage and the loosened cap.
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The required amount of pressure is thus not created by the engine, and rough and noisy sounds are observed. This creates the engine code P0174.
The engine code P0174 may appear due to the block fuel filter. The fuel filter can get blocked due to dirt and debris. Due to the block filter, the required pressure would not be created, causing the engine to be too weak and idle. Also, the damaged vacuum pump can affect the engine’s performance (3). Due to vacuum leakage, a large amount of fuel is consumed, making it difficult to start the engine. As a result, the air-to-fuel ratio is disturbed, and engine code P0174 is shown.
Symptoms of P0174 DTC
Increased Fuel Requirement
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The major symptom of engine code P0174 is the large consumption of fuel. This symptom indicates that the engine is not performing properly and requires more fuel.
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This usually happens when air to fuel ratio in the engine is disturbed. For example, the ratio gets disturbed when the max airflow sensor is damaged and not providing accurate information about the air in the engine (5). Also, a large amount of fuel will burn due to defective oxygen sensors and mass air flow sensors, releasing black-colored smoke from the exhaust system. These issues are a clear indication of engine code P0174.
Misfiring Engine and Idle Engine Performance
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Another major symptom of the engine code P0174 is the misfiring in the engine’s cylinder. The misfire in the engine usually takes place when less amount of power is produced in the engine.
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Less fuel pressure is generated when there is any leakage in the fuel pump or it has to become weak (1). Due to the less pressure, the spark is not created in the engine easily, making it very difficult to start the car. In addition, due to minimum production of power, the car fails to accelerate at high speed, and the engine ceases after traveling a few miles. Besides, the misfire can also occur due to dirt and damage in the cylinders, which is the major reason for an idle engine (5). The rough and noisy sounds are observed, and the engine light is indicated on the dashboard due to engine code P0174.
Solution of P0174 DTC
Clean the MAF Sensor or Its Replacement
The MAF sensor is usually between the engine manifold and the air filter. It gets dirty due to dust on the air filter, which can impact the readings of the MAF sensor. You can clean the MAF sensor with the soapy solution and test drive the vehicle. If the DTC appears again, then replace the MAF sensor. You can consult the vehicle’s instruction manual to detect the right location of the MAF sensor and its specifications (4). Many drivers make mistakes in ordering the wrong sensor that does not support their vehicle model. In this case, DTC will occur again.
Clean the Oxygen Sensor or its Replacement
The oxygen sensor is located in the exhaust on the car’s passenger side just after the catalytic converter. An oxygen sensor can get dirty due to the exhaust gases and carbon particles escaping through the catalytic converter. In this case, you can try cleaning the oxygen sensor with the soapy solution and test-drive the vehicle (3). Suppose the vehicle shows the same symptoms as a rough/idle engine. In that case, it is time to replace the oxygen sensor. It is again recommended that the drivers check the sensor specifications before ordering one to avoid any inconvenience.
Reset the DTC and Test Drive the Vehicle
Like every DTC, this DTC can also result from an error in the ECU. If your car does not show signs of P0174, then it is better to reset the DTC and test-drive the vehicle. This can be done by connecting the hand-code reader with the OBDII module, which will provide an option to reset the DTC. But, first, test-drive the vehicle to ensure that the DTC does not appear again.
Replace the Fuel Pump Components
As discussed above, the fuel pump components’ error can also cause P0174 DTC. The fuel pump will struggle to inject the right amount of fuel into the engine cylinder, causing a lean condition. In this case, you are recommended to take the car to a professional mechanic to get the faulty components replaced (4). This can include faulty injectors, rusted fuel tanks, etc. Replacing these components will optimize fuel pump performance, improve engine performance, and alleviate the lean condition.
Cost Required to Resolve the Issue
The following table illustrates the typical cost of resolving 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
Faulty Fuel Pump Components
High: A faulty fuel pump will cause lean conditions, even failing internal engine components
$100-1500 to replace faulty fuel pump components, depending on the failure.
Conclusion
To conclude, P0174 is a severe intermediate DTC, indicating lean condition at engine bank 2. It can occur due to faulty oxygen sensors, MAF sensors, and faults in the fuel pump components. In rare cases, a clogged air filter can also light up the check engine light indicating lean condition at engine bank 2. So, suppose you are experiencing a rough engine and a decrease in fuel economy. In that case, the DTC P0174 may have occurred in your vehicle.
Yes, driving the vehicle on long routes with this engine fault code is risky. It is because faulty oxygen sensors and fuel pump components can cause a lean condition in the engine. This means that the engine is provided with too much fuel or air, resulting in engine component failure in the longer term. So, you must replace the faulty components earliest to avoid any costly engine damage.
In most vehicle models, the MAF sensor is located between the engine manifold and the air filter. So you can easily locate this sensor. However, if you find it difficult to locate this sensor, you should consult the vehicle’s instruction manual. You can easily find the instruction manuals online by putting in the vehicle’s model and variant.
The DTC signifies that either sensors or the fuel pump are faulty. In rare cases, the air filter can cause this problem. If you see P0174 DTC on the hand-code reader, you are recommended to clean the sensors first and test-drive the vehicle. The second step should be to observe the filters, and the last step should be to analyze the fuel pump. Fuel pumps are generally sturdy and get worn out after a considerable time.
