How To Fix P0172 Obd2 Code (Causes, Symptoms & Diagnosis)

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The ignition and combustion rely heavily on the interaction of air and fuel. In order for the ignition to take place, the chamber of internal combustion must be supplied with the right quantity of air and fuel. Otherwise, you risk having your engine use too rich fuel conditions or not operate as well as it might.

Standard operating procedure calls for the engine control unit (ECU) to manage how much air and fuel are introduced to the combustion chamber. Including the amount of gasoline fed into the combustion chamber, this central computer controls nearly all of the vehicle’s internal processes.

However, the engine may get more gasoline than it needs to maintain the vehicle’s power demands once the computer becomes malfunctioning or if there are other difficulties with the fuel injection system. Due to this, you’d get the P0172 code with the Professional obd2 Scanner that is actually generated by the ECU.

Code Definition: P0172

When the engine control unit (ECU) detects that the fuel has a way higher proportion in the air-fuel combination, it stores a fault code (P0172). To get the most out of your engine and the most efficient fuel consumption, you need to maintain an air-fuel ratio of roughly 14.7:1.

The fuel injection system’s sensors are continually being monitored and communicated with by your engine control unit. Diagnostic problem code (DTC) P0172 is generated by the powertrain if the unit detects an excess amount of fuel in the combustion chamber.

The amount of fuel in the chamber’s exhaust gasses is measured using a number of sensors and equipment. The absolute pressure in the manifold, mass air flow, and oxygen sensors are among the examples. Too rich a fuel condition indicates a lack of oxygen.

The first cylinder, or “cylinder 1,” is located in what is called “Bank 1” of the engine. Using oxygen sensors, we can determine how much oxygen is present in the flue gas leaving this cylinder.

Insufficient oxygen detected by the sensors indicates that the air-to-fuel ratio is off. With most gas-powered vehicles, the standard ratio is 14.7:1.

This particular ratio maximizes the engine’s efficiency, allowing it to provide maximum output while burning the minimum quantity of gasoline. For the engine control unit, a too rich condition in bank 1 indicates an excess of fuel relative to oxygen proportion.

Error code P0172: Causes, Symptoms & Diagnosis


When you get P0172 code with Obd2 Scanner With Live Data on your hands, there are some possible causes. Over fueling can result from a faulty mass air flow sensor that incorrectly reads the air level entering the combustion chamber. Aside from that, these are some other possible causes:

  • Poor oxygen sensor quality
  • Over fueling due to a faulty fuel injector that leaks fuel into the engine
  • The fuel pressure going into the engine may not be being controlled properly due to a defective fuel regulator.
  • A problem with the cooling system, such as a malfunctioning thermostat or temperature sensor.
  • An air leak
  • Spark plug wear


Typically, you’d notice at least one of these symptoms if you have P0172 code problems:

  • MIL is illuminating
  • Unusual Poor Mileage
  • The tailpipe is billowing black smoke
  • Engine idles roughly
  • Misfiring issues
  • The exhaust has a strong odor of petrol.
  • Spark plug diode clogged with soot.

When you notice any of these symptoms, you need to grab an OBD2 scanner like Autel Maxicom Mk808bt to get the DTCs and perform visual inspection whenever possible.


When trying to figure out what’s up with P0172, it’s crucial to run through every possible diagnostic step. As soon as they obtain a bad signal, many individuals rush to repair or even replace the corresponding sensors. However, a filthy or malfunctioning mass airflow sensor or vacuum leak may actually be the real culprit.

You can grab a compatible OBD II scanner like Innova 3020 or others, and perform these diagnoses below to obtain a solid overview of the actual problems.  

  • Inspecting any irregularity with the fuel pressure
  • Checking the fuel injector pulse with loud lights
  • Examining the car for air leaks
  • Examining the Sensors for Oxygen and Air Flow
  • Examining for Blockages in the air intake system

Common Diagnosis Mistakes when diagnosing P0172 Obd2 Code

When trying to figure out what’s up with P0172, it’s crucial to finish the diagnostic process in its entirety. A vacuum leak or bad sensors on the Oxygen and/or the MAF is commonly the cause of bad reading, although many individuals rush to replace the O2 or A/F right after getting the code. 

To correctly diagnose a P0172 code requires thorough reading and analysis of the fuel trims and freeze frame data with a proper scanner like Foxwell NT809 or comparable scan tools.

How to fix obd2 code P0172

DTC P0172 can be caused by various factors, making accurate diagnosis and repair difficult. At this point, you always better go to the simplest solutions first before repairing or replacing the suspected components.

  1. Start with the most basic (and inexpensive) checks, such as making sure the air filter and the Mass Air Flow(MAF) sensor are clean. Whenever possible you can unclog any blockage.
  2. It’s easy to make the incorrect assumption that you need to replace your vehicle’s oxygen sensor or air/fuel sensor.
  3. Fixing any vacuum leak 
  4. Repairing your vehicle’s fuel system by swapping out a malfunctioning fuel injector, pump, and/or the regulator
  5. When an air filter becomes too congested, it must be replaced with the new one
  6. replacing the thermostat and/or the sensor for coolant temperature
  7. Cleaning or replacing the spark plugs
  8. Cleaning sensors for mass airflow and oxygen

Tips to avoid in future

Checking the quality of the spark plugs and making sure the coolant temperature sensor is working properly is something that is strongly advised. This maintenance would prevent you from getting the P0172 code.

If you already have an OBD2 Scanner for DIY in your garage, it’s also handy to run a diagnostic on a regular basis to see whether or not you have this particular code in your vehicle.


The P0172 code can be sent by the ECU for different reasons. Performing proper diagnostics would help you find the actual problems so you can apply the proper troubleshooting as well. Whenever you notice something related to P0172 you better grab your scanner and perform a diagnostic. Fast responding to any symptom would prevent greater damage to your engine in this case.

How to Fix P0172 Engine Code in 2 Minutes [2 DIY Methods / Only $8.77]
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