P0172 Engine Trouble Code Help & Fix

What is the P0172 Code?

P0172 is a trouble code that is set when the ECU senses that there may be too much gasoline present in the air-fuel mixture of the engine. A proper air-fuel ratio of about 14.7:1 is vital to obtain maximum engine power and fuel economy.

The P0172 code indicates that there is too much gasoline being detected in the exhaust gasses exiting the combustion chamber. The ECU uses a number of instruments, such as the mass air flow sensor (MAF), oxygen sensors, and manifold absolute pressure (MAP) to monitor the air-fuel ratio of the engine.

Most routinely, the air-fuel ratio will be measured through the oxygen sensors calculating the amount of oxygen and carbon monoxide present in exhaust gasses. The best air-fuel ratio modernly known to man is 14.7:1. This particular ratio was chosen because it was discovered to have the highest power output but lowest fuel consumption rate.

The ECU has the ability to slightly adjust the air-fuel ratio if it is rich. However, if the margin of compensation is too large, then a P0172 code will likely be triggered. The term “rich” in this case means that there is too much gasoline and not enough oxygen detected in the air-fuel ratio of the engine.

P0172 Code Causes & Symptoms

P0172 Code Causes

There are many different factors that could cause the P0172 code to be triggered in your vehicle.

Here are the most common causes of the P0172 code:

• A dirty mass air flow sensor overstating the amount of air entering the engine which may cause excessive fuel delivery
• A bad oxygen sensor
• A leaking fuel injector allowing too much fuel to enter the combustion chamber
• A faulty fuel regulator, which may not be regulating the pressure of the going to the engine as it should
• A vacuum leak
• A possible fault in the coolant system such as a stuck thermostat or bad coolant temperature sensor
• Worn spark plugs

P0172 Code Symptoms

The P0172 code often shows many noticeable symptoms and needs immediate attention to prevent further damage and ensure optimal engine performance.

Here are the most common symptoms of a P0172 code:

• A Check Engine Light being set
• Higher fuel consumption
• Black smoke coming from the exhaust

P0172 Code Diagnosis & Mistakes

The following steps outline how a mechanic commonly diagnoses a P0172 code:

• By performing a fuel pressure test
• Using noid lights to check fuel injector pulse
• Checking the vehicle for vacuum leaks
• Inspecting the Mass Air Flow Sensor and Oxygen Sensors
• Checking the Air intake system for clogging

The most common mistake associated when a P0172 code is diagnosed by a mechanic is not inspecting the coolant temperature sensor and cooling system. When the engine is cold, more fuel is added to help warm it up to a desirable temperature. If the coolant temperature sensor is not sending the proper signal there is a possibility that the engine ECU may assume that it is always running cold.

How Serious is the P0172 Code?

The severity of the P0172 trouble code shouldn't be underestimated, as it can lead to significant consequences for your vehicle's performance. One immediate concern is the potential failure to pass state vehicle inspections due to the illuminated Check Engine Light triggered by the code. Moreover, the presence of a rich air-fuel mixture, indicated by P0172, can result in the emission of black smoke from the exhaust. Not only does this compromise engine efficiency and performance, but it also poses environmental hazards by releasing harmful pollutants into the air. Addressing the P0172 code promptly is essential to ensure compliance with regulatory standards and minimize harmful effects on your vehicle.

How to Fix the P0172 Code

These are the most common ways to fix a P0172 code:

• A repair of a vacuum leak
• A replacement of a faulty fuel injector, fuel pump, or fuel regulator
• Replacement of an excessively restricted air filter
• Replacement of the thermostat or coolant temperature sensor
• A replacement of the spark plugs
• A cleaning of the oxygen sensors and mass air flow sensor

Additional Comments & Help with the P0172 Code

It is highly recommended to check the condition of the spark plugs and the operation of the coolant temperature sensor as these are commonly overlooked causes of the P0172 trouble code. If you’re dealing with the P0172 code, YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.