What is P0172 DTC? Common Symptoms, Causes, and Solution
P0172 indicates that the sensor detects too much fuel in the exhaust gases exiting the engine’s combustion chamber. It is a serious warning and should not be ignored!
The following are the key takeaways from this article:
P0172 is a standardized SAE engine fault code indicating rich condition near engine bank 1.
This code can occur due to faulty sparkplugs, faulty fuel injectors, defective throttle position sensors, vacuum leaks, and defective manifold position sensor/oxygen sensor/MAF sensor.
The possible symptoms of this fault code include a misfiring engine, less fuel efficiency, and less power delivered by the engine, followed by black smoke out of the exhaust.
The common solutions for this DTC include resetting the DTC, replacing the fuel pressure regulator, replacing the sparkplug, and replacing/cleaning the faulty sensors.
The cost of resolving this DTC can vary between $20 to $2500.
Introduction
Several sensors, such as MAF (mass air flow), oxygen sensors, and manifold absolute pressure (MAP), monitor the air-fuel mixture entering the engine’s cylinder. It is suitable to maintain an optimum air-fuel mixture for maximized engine performance. Your vehicle’s ECU receives information about the exhaust gases leaving the car through these sensors (1). And it eventually decides the right amount of fuel to be injected into the car’s cylinders. Modern vehicle manufacturers have introduced engine fault codes that indicate lean or rich engine bank conditions to avoid damage to the engine components.
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P0172 is an engine fault code indicating that the fuel system near bank 1 is too rich. In simpler words, the sensors analyze too much fuel in the exhaust gases.
This article will further analyze the causes, symptoms, and solutions of the P0172 engine fault code.
How to Read P0172 DTC
The following table has read every character of P0172 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
72
The specific fault index is 72, indicating that the system near engine bank 1 is rich.
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P0172 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 2.
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Causes of P0172 DTC
Defected Fuel Injectors and Spark Plugs
The major cause of the engine code P0172 is the defective fuel injectors. Fuel injectors have a vital role in maintaining the engine’s performance; the main purpose is to limit the amount of fuel.
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It allows a limited amount of fuel to enter the combustion chamber. It means the correct amount of fuel is entered at the right times. When the fuel injector gets damaged due to dirt and debris, a large amount of fuel will enter the combustion chamber, unbalancing the engine’s air-to-fuel ratio. Due to the combustion process, more fuel will be burnt, and black-colored smoke will release from the exhaust system (1). Also, the deposition of oxides in the combustion chamber will be responsible for the rotten smell from the engine.
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Other than it, the faulty spark plugs can be of the engine code P0172. The spark plugs can get damaged due to the coverage of oil, dirt, and debris; fuel ignition is delayed. Thus, it results in limited car acceleration as engine performance deteriorates.
Defected Throttle Position Sensor
Another cause of engine code P0172 can be the defective throttle position sensor. The throttle position sensor has a specific role in the vehicle, and the main purpose is to monitor the amount of air entering the engine.
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Due to the damage, the throttle position sensors fail to determine the amount of air in the engine, and wrong information is sent to an electronic control unit (2). Thus, the engine’s performance is impacted, and as a result, the vehicle’s speed is not maintained. Also, to avoid any incident, the engine light is indicated on the dashboard to indicate the error code P0172.
Defected Manifold Absolute Pressure Sensor
The Manifold absolute pressure sensor plays a very different role. The purpose of this sensor is to predict the amount of fuel and air required for ignition in the cylinder (3). Also, the MAP sensor calculates the cylinders’ vacuum, which constantly changes depending on the engine load.
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Thus, the defective MAP sensor can be the reason for the engine code P0172, as the wrong amount of vacuum in the engine will be detected. It will result in minimum power generation.
Vacuum leak and Defective Air Filter
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There is a possibility that due to the vacuum leakage and the defective air filter, the engine code P0172 can be generated.
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This is because the clogged air filter will unbalance the amount of air in the engine, and as a result, the engine will become weak and idle (2). In addition, vacuum leakage occurs due to loosening caps, minimum pressure is generated, and less acceleration is produced. Thus, the engine light is on the dashboard, indicating the error code P0172.
Symptoms of P0172 DTC
Lack of Power
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The major symptom of the engine code P0172 is the minimum power generation. Due to the minimum power generation, the vehicle fails to accelerate at high speed, and the engine stops working after certain intervals.
The minimum power is generated due to the manifold absolute pressure sensor error. Due to the defective manifold absolute pressure, an accurate prediction regarding the fuel and air is yet to be made. As a result, the air-to-fuel ratio is disturbed (3). These cause difficulty in fuel ignition; thus, the required amount of power is not generated.
Engine Misfired
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The other major symptom of the engine code P0172 is the engine misfire. Engine misfire usually occurs when there is an error in the spark plugs and fuel injectors.
Due to the error in the fuel injectors proper amount of fuel is not supplied to the combustion chamber, and the air-to-fuel ratio is unbalanced. This becomes the major reason for the engine misfire in the cylinders. Also, due to the damaged spark plugs, the process in the combustion chamber is delayed. Also, the common symptom of engine code P0172 is the black-colored smoke from the exhaust system (1). This happens when more amount of fuel is burnt during the combustion process.
Poor Fuel Economy
A defective fuel injector affects the flow of fuel to the combustion chamber. Thus due to the poor fuel injector, the required amount of fuel will not flow in the chamber, and the car consumes more fuel during traveling (5). Also, the engine faces poor fuel economy due to clogged air filters.
The amount of air to fuel is disturbed, and as a reaction, the engine’s performance gets poor. Also, the engine light is indicated on the dashboard to indicate the error code P0172.
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Solutions of P0172 DTC
Following are a few common solutions of P0172 DTC:
Reset the DTC and Test Drive the Vehicle
Sometimes, engine fault codes occur due to an error in the ECU, and a wrong code is displayed on the hand-code reader. In this case, the driver would not observe common symptoms such as a misfiring engine, lack of power, less fuel mileage, etc. Any DTC, including P0172, can be reset by connecting a hand-code reader with the OBDII module (3). It would display the particular DTC and provide you with an option to reset the DTC. However, test drives the vehicle to ensure the warning light does not illuminate and the DTC does not appear again.
Replace the Fuel Pressure Regulator/Fuel Injector
Another solution for this DTC is to replace the faulty fuel injector/pressure regulator. Sometimes, the clogged injectors can be cleaned by professional mechanics. A professional can run tests such as fuel pressure gauge test using parameters such as vacuum, air-fuel mixture, fuel pressure, etc. (4). If the air-fuel mixture, vacuum, pressure, etc., lie within the manufacturer specifications, then the fuel injectors do not require replacement and vice versa (2). So, you are recommended to take the car to a professional mechanic, and the fuel injectors are not performing optimally.
Replace the Sparkplugs
Another solution for this DTC is to replace the faulty spark plug. A typical engine has one sparkplug per cylinder, and there can be a chance that the sparkplug near bank 1 is faulty. In this case, you can replace the faulty sparkplug (5). The sparkplugs are typically located above the engine cylinder and can be accessed by a simple driver. So, you can order the sparkplugs online and replace them yourself (4). However, ensure that you consult your vehicle’s instruction manual before ordering the sparkplugs to avoid any inconvenience.
Replace or Clean the Faulty Sensors
As discussed above, a major reason for this DTC can be a fault in the oxygen sensor, MAF sensor, etc. The solution is to clean these sensors and test drive the vehicle. The location of these sensors makes them dirt-sensitive, so dirt is deposited over these sensors. Resultantly, the sensors are unable to send the right information to ECU. In this case, you can access the sensors and clean them with a soapy solution (4). The MAF sensor is located between the intake and the air filter and can easily be accessed.
Similarly, the oxygen sensor is located in the exhaust and can be easily accessed too. In both cases, clean the sensors and test-drive the vehicle. But if the vehicle malfunctions after cleaning the sensors, it is better to replace them with new ones. Again, these sensors are inexpensive and can be ordered online. But it is recommended to replace the sensors by visiting a professional mechanic to avoid circuitry issues.
Common Cost to Resolve P0172 DTC
The following table illustrates the cost of resolving P0172 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 Catalytic Converter
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, P0172 is an intermediate/severe DTC that indicates a rich air-fuel mixture in engine bank 1. This condition should be fixed quickly to avoid any internal engine component damage that can be costly to resolve. This error can occur due to vacuum leakage, faulty sensors, fuel injectors, sparkplugs, etc. So, if you are experiencing decreased engine power and reduced fuel mileage, it is a sign that the DTC is P0172 and the air-fuel mixture is rich.
Although a clogged air filter does not cause a rich condition in the engine bank, there can be a possibility that the air entering the engine is less, so the ECU has to increase the fuel supply for combustion. Usually, the clogged air filter will cause DTC P0171, which indicates a lean condition in the engine bank.
P0172 DTC is a serious condition as it increases the fuel supply to the engine. Firstly, you will experience rich conditions in the engine so that the fuel mileage will be decreased automatically. In this case, you must supply more fuel for the vehicle to travel. Further, extended driving in this condition can cause internal engine component damage that can be costly to resolve, depending upon the nature of the engine damage.
Yes, P0172 is an SAE standardized code. The second character of the DTC illustrates whether a code is SAE standardized or not. For example, ‘0’ illustrates that the code is SAE standardized, and this code will have the same meaning in every vehicle model. However, ‘1’ will illustrate that the code is different and manufacturer specific.
